P-38 Skin Build Log

[oboe]

Yes, thanks for that explanation, Greebo.   

[Greebo]

Part Two: UVs and Panel Line Layout

Laying out the UVs

Now the files and basic lighting are set up its time to start some creative skinning by laying out my UVs. Opening my working file I first disable the UV mapper layer and create a new layer which I call “Olive drab”. This will eventually form the base layer of my camouflage scheme. On this layer, using the default skin as a guide, I begin drawing 3 pixel wide lines in light grey around the borders of each of the areas on the bmp that form the outside of the aircraft; the wings, booms, fuselage and tail etc. These shapes are then filled using the flood fill tool. One tip when doing this is to turn off anti-aliasing for the line tool used for drawing the UV borders. As I forgot to do this it meant the aliased lines created an inner border of semi-transparent lines around the edge of my UVs that I had to take time to correct. Once I think I have all the UVs mapped I do a “save as bmp” and check the skin in the viewer. Now almost all the painted areas of the aircraft are painted a light grey shade which will show up the panel lines well. However I have missed a couple of bits, the radio mast and the canopy so I fill these in on the bmp and re-check in the viewer.

Now the external painted areas of the skin has its UVs I want to do the same to the remaining small parts on the aircraft like the gear and gear bays, turbochargers, guns etc. Now there is a convention in AH skinning that you only need to reskin the main airframe and these small parts from the default skin can be retained. However I do intend to repaint or modify some of these small parts and so I want their UVs mapped out. The process is the same as before, create a new layer called “Small part UVs”, draw the outlines using a line tool then flood fill the shapes. To differentiate this layer I use blue rather then light grey.

One final thing I do with the UVs is to check their borders. To do this I create a new layer placed between the UV layers and the default skin layer. I call it “Test fill”, flood fill it with a bright yellow colour and check the results in the skin viewer as per the screenshot below. Wherever there is yellow peeking through the grey then one of the bordering UVs needs to be extended on the bmp to cover the gap. Once all these gaps have been eliminated the UVs are done and can I disable both the Test fill and the Small parts UVs layers.



Before going any further I do some layer house keeping. I move all the layers that are not going to be part of the final skin, such as the UV mapper and the Test fill into a new layer group called “Unused layers”. The Olive drab layer goes into a group called “Paint and materials”.

Source Material

Now before I move onto drawing the panel lines I need some source material to reference. First I check the default skin but it quickly becomes apparent it is not going to be much use to me. Its panel lines were obviously created for a P-38J rather than a G, the main spar lines are placed too far back on the wing and some of the control surface and gear door hinge lines on the skin do not match these hinge lines' positions on the 3D shape.

So rejecting the default skin as a reference I decide to use panel line diagrams and close up photos instead, both of which can be found in books and on the web. In general aircraft books by publishers like Squadron/Signal, SAM, Kagero, Wydawnictwo Militaria and Bunrindo tend to have a lot of this sort of info while other publishers' books may concentrate more on an aircraft's history and development.

On the web a search for “P-38 walkaround” reveals a load of sites with close up photos of P-38s taken at museums or air shows. Close up photos are a good back up for when a diagram isn't clear and I usually download a load of these and organise them into seperate folders for wings, tail, gear and so on.

 Anyway in my books and on the web I find loads of  walkaround photos and panel line diagrams for the P-38J and L but not much for the earlier variants. However a search for “Glacier Girl” reveals a few photos of the P-38F dug out of a glacier and restored a few years back and the Squadron/Signal D&S Scale book No 57 covers the earlier variants. In the end I make a careful note of  the external differences between the G and J/L (cowlings, radiators, wing tanks, canopy, recovery flaps) so I can still use most of the J/L data for this skin.

For panel line diagrams I use a simple one for the P-38E and a much better one with rivet detail on it for the P-38J. The relevant parts of these I copy and paste into my skin into a “Panel line diagram” layer, scaling the parts to fit the 3D shape as best I can.

Drawing the panel lines

To start with I create five new layers; “ Horizontal panel lines”, “Vertical panel lines”, “Raised panel lines”, “Fasteners” and “Small hatches” all of which go in their own layer group called “Panel lines”. This is placed above the “Paints and Materials” layer group and also above the “Panel line diagram” layer, which I reduce in opacity to make it less visible.

So why all these different layers just for panel lines? Couldn't I make do with only one? Well I find doing it this way gives a much better end product and makes the lines much easier to edit. A good rule of thumb regarding layers in any sort of computer art is that if unsure about whether to go for one or many layers for something, go for many. It is a very simple matter to merge these many layers later on but it can be difficult or even impossible to split the data from one into more layers later on.

The horizontal and vertical panel line layers describe how these lines are laid on the bmp, not how they relate to the 3D shape. Splitting them like this means I can later move a vertical line a couple of pixels left or right without disturbing the horizontal lines that may run though, above or below it. Angled or curved lines are assigned to whichever layer makes them easier to edit.

The raised panel lines layer is for those lines that represent the edges of panels that are significantly raised above the surface of the skin, things like the fairings fastened over the joins between the wings and fuselage. Later on I will use these lines to create raised edge lighting effects in the diffuse and normal maps.

The fastener and small hatches layers are self explanatory and have their own layers partly for ease of editing and partly so I can vary their opacity independently from the other lines later on.

I like to skin each layer with differently colour lines for clarity, purple and blue for the main lines, red for the raised, black for the small hatches and green for the fasteners.

So what lines to draw first on the skin? Well I like to start with any lines whose position is dependent on the 3D geometry of the shape. This means things like control surface hinge lines and gear door lines. For the most part I turn on the default skin layer to see where to place these on the bmp and then turn it off before viewing the result in the viewer. In this case I had to edit these lines a few times to get them exactly placed. Once these 3D geometry-fixed lines are in place the rest of the lines can be placed using them as another reference. The screenshots below show the process:-



In this case I start at the LH nacelle/wing join and work out from there since this area looks to be the most challenging to get right. I reference both the panel line diagram I pasted in and lots of close up photos of the area I am skinning. The photos help me understand which lines are hatches, raised fairings or panel join lines so I can see which layers to draw each line on. Sometimes I have to nudge a fastener or line up or down a bit to avoid it getting blurred due to the texture stretching I mentioned in my first post.

Expanding out I skin all the main panel lines across the LH half of the aircraft, then all the small hatches and fasteners. The photos show that the real cowling fasteners were a bit bigger than all the little hatch fasteners so I make the former 3 pixel circles and the latter 1 pixel dots.  So that I can later vary the opacity of each of these independently I split the fastener layer into two, for small and large fasteners.

After this post my next job will be to place all the rivets on the LH side of the aircraft. I'll do this before copying and pasting all the panel lines and rivets from the LH side over to the RH side. This is because I often discover little errors in my lines while placing the rivets and it saves me having to alter the lines on both halves of the skin each time. Once I copy the lines across I will then have to edit them for any left/right differences in hatch placement etc.

Creating a scaling mask

With all the LH panel lines in place I can see the difference in line visibility caused by the scaling mismatch issues I mentioned in the first post. The lines on the tail are much wider and so more visible than those on the rest of the aircraft due to the tail's relatively small size on the bmp.

So to reduce these thick lines' visibility I am going to create an opacity mask layer. I hit the mask layer button, set it to “show all” and place it as the top layer in the panel line group. Currently the mask layer is entirely white and so shows everything from the panel line layers below it. Making areas of the layer grey or black will make those specific areas of the panel line layers less visible, the darker the grey the less visible those lines will be. So in this case I copy the uvs of the horizontal tail from the olive drab layer, turn them black and paste them into the mask layer. I do the same for the vertical tail and canopy uvs except to turn these mid grey. Reducing the opacity of the mask layer causes the horizontal tail lines to reappear and I adjust the opacity to get the effect I am looking for. In the final stages of the build I'll tweak all these layer opacities again. The screenshots below show the mask and how it works:-

Another method I could have used to do this would have been to use an eraser tool to partially erase the fat lines in each layer directly. However this would have been difficult to tweak later on. Besides I can now quickly copy and paste this mask into other groups I intend to create for things like rivets.

That's it for now, hope this was informative to some of you.

[Vraciu]

I love the idea of vertical and horizontal panel line layers.    Brilliant. 

I had mine broken down differently.   Flaps and Aileron, Cowling, Upper Wing, etc.     vertical and Horizontal along with something for Flaps and Aileron, etc. would make my life much easier.   

Opacity masks?   I like that, too. 

Good stuff. 

[Devil 505]

Great stuff Greebo.

[Greebo]

I love the idea of vertical and horizontal panel line layers.    Brilliant. 

I had mine broken down differently.   Flaps and Aileron, Cowling, Upper Wing, etc.     vertical and Horizontal along with something for Flaps and Aileron, etc. would make my life much easier.   

I'm going to alter and add to the panel line layers later on in the build. Once I am past the editing stage the vertical and horizontal layers will get merged and a copy of this layer then used to create a heavy panel line layer. The raised layer will be used to create some edge shadows and highlights.

I prefer not having different layers for specific areas like the wing or tail as it makes it more difficult when it gets to the tinkering stage. My way if I want to reduce the opacity of the panel lines I can do it with one layer slider for the whole skin and there is no chance of forgetting to alter one area of the skin. The alternative would be to put all your individual part layers in a group and use the group slider to achieve the same thing but my way seems simpler to me.

[Vraciu]

I'm going to alter and add to the panel line layers later on in the build. Once I am past the editing stage the vertical and horizontal layers will get merged and a copy of this layer then used to create a heavy panel line layer. The raised layer will be used to create some edge shadows and highlights.

I prefer not having different layers for specific areas like the wing or tail as it makes it more difficult when it gets to the tinkering stage. My way if I want to reduce the opacity of the panel lines I can do it with one layer slider for the whole skin and there is no chance of forgetting to alter one area of the skin. The alternative would be to put all your individual part layers in a group and use the group slider to achieve the same thing but my way seems simpler to me.

Can’t really argue with your logic.   I’ll be borrowing some of your ideas on this one.  Good stuff. I still have to separate some of my panel lines by type because the opacity varies (I suspect later posts by you will solve that riddle), but my organization could use some help.  Breaking out the vertical and the horizontal is a brilliant idea. 

[steely07]

This stuff fascinates me, I've always been interested in the work that goes on behind the scenes, thanks for doing this Greebo, subscribed, can't wait for the next post <S>!

[puller]

Yes...great stuff greebo...thanks for laying this out for us

[Greebo]

Part 3: Placing rivets and finishing the panel lines

Rivets

For the rivets I start by creating vertical and horizontal rivet layers. As with the panel lines, this makes the rivets easier to edit. These two layers are placed into a new “Rivets” folder to keep the layer stack neat and tidy. A copy of the opacity mask I created for the panel lines is then pasted to the top of this new folder.

Moving to the horizontal rivet layer, I select a one by five pixel area, flood fill it with yellow and then move each of the five yellow pixels by hand into a horizontal line of one pixel dots spaced one every four pixels. Then I copy and paste these five rivets into a much longer line. The idea is the three pixel gap between these rivets can bridge a one pixel wide panel line without either rivet touching the line.

With my rivet line created I begin copying and pasting it onto the upper LH wing for the ribs. To help do this I use the panel line diagram layer's rivet layout as a rough placement guide. Some rivets occasionally need moving a pixel or two to avoid touching a vertical panel line. Sometimes though I'll move a panel line or small hatch a few pixels to keep the rib spacing even.

Once all the ribs are placed I switch to the vertical rivet layer, paste a rivet line in, turn it 90 degrees, make it light green and then copy and paste this a few times to make a longer vertical line for the main spar. Where this line crosses a horizontal rivet line or panel line I space the rivets out to avoid them  touching. With this vertical line done I copy and paste it across the wing, moving rivets to angle the lines as needed. It is then the same process with the lower LH wing, booms, fuselage and vertical tail. The horizontal tail however is so far out of scale the rivets would look far too big on it, so I skip that part.

This method of copying, pasting and positioning lines of dots is tedious to do but I've not found any other way to get lines of sharp one pixel rivets. It might seem easier to create a custom dotted line tool and then use it to lay out the rivet lines but I find the rivets this creates are blurred, and look rubbish at this low a resolution.

Here's what the rivets look like once they are done:



Pasting across the lines and rivets

With the panel lines and rivets now complete for the LH side of the skin it is time to copy and paste them across to the RH side. Best bet here is to start with the fuselage's vertical and horizontal panel lines, get the RH side's horizontal and vertical fuselage panel lines to match the left side's, then paste in the other fuselage layers. Next paste across the upper and lower wing panel lines, get these to match both each other, the RH fuselage's lines and also the aileron and flap breaks on the 3D shape, then paste across the other wing layers.  Then in the same fashion paste across the booms and vertical tail.

Once everything has been moved across it is time to examine the panel line diagrams and photos for differences between the right and left side of the aircraft. On the P-38G there are quite a few hatches that only appear on one side or other of the fuselage, booms or vertical tails and the landing light was only fitted below the LH wing. So armed with this information it is just a question of editing the RH side of the plane; moving, adding or deleting the incorrect hatches, fasteners, lines and rivets until everything looks right.

Before going any further I take the precaution backing up the working file, better safe than sorry.


Finalising the panel lines

With the aircraft completely panel lined and riveted I can now dispose of the gaudy false colour lines and merge the horizontal and vertical layers. Both were useful tricks while I was editing these layers but not now they are finished.

Selecting the vertical and horizontal panel line layers, I duplicate both and then merge these duplicates into one layer I call “Panel lines”. The original vertical and horizontal layers are moved into the “Unused layers” group. Next I merge duplicates of the rivet layers, again putting the originals into the unused layers group. I'll need these editable layers again when I eventually turn this P-38G template into a P-38J/L one. Besides its always good to create back ups when doing something irreversible like merging layers.

Selecting each of these layers in turn I change all the lines and dots on them black, except for the raised panel lines layer which I turn white. Easiest way to do this is to change the brightness of each layer to maximum or minimum. Next I adjust the opacity of all the black layers to make the overall effect look more realistic, the rivets are set to 10% opacity, the panel lines, the fasteners 40% and the small hatches 70%. This is just a first pass, all these values will likely be readjusted more than once before the scheme, weathering and lighting effects are all done.

It seems the light grey base I have been using for this skin is getting a bit washed out by the skin viewer's lighting. So to allow the now toned-down detail on the skin to be better seen I make the base grey a darker shade,

Now there are a couple more things I want to do with the panel lines. The first is to create a new layer I call “Raised panel shadows”. With this layer selected I choose a one pixel line tool with red as the line colour for clarity. Using this I draw lines adjacent to the white raised panel lines but on the non-raised panel side of the white line only. The idea here is that the white line is the highlighted edge of a raised panel and the red line, once turned black, will be the shadow cast by this raised panel. This 3D effect will be boosted once the normal map is done, as directional shadows and highlights will also be cast by the the raised panels. After all the shadow lines are drawn I check the result in the viewer, editing as necessary. Once I am happy I turn the red lines black and adjust both the raised line layers' opacity. The screenshots below show the idea:





The other thing I want to do is create a heavy panel line layer. Lines on the real plane are caused by a mixture of hinge lines, gear doors, large access hatches and also the joins between riveted-together aluminium panels. The latter lines tend to be less visible to the eye than the other lines and I want to copy this effect on my skin. So I make a duplicate of the panel line layer, call it “Heavy panel lines” and turn all the lines on it red for clarity. Then I carefully erase all the lines on the layer that I do not want to be heavy, just leaving things like the gear doors, engine and armament hatches and the control surface and trim tab lines. After checking these red lines look correct in the viewer I edit them as needed, turn them black and then adjust the layer's opacity as needed. The screenshots below show the idea:





This is the current progress:




That's it for now, next time I will add some shadows.

[Greebo]

Part 4: Adding shadows

Ambient Occlusion

In this part of the build I am going to add some shadows to the skin. While the game engine can add directional lighting and shading calculated from inputs such as the position of the sun, the shape of the aircraft and surface data from the normal map, what it can't do is ambient shading.

So what do I mean by ambient shading? Well imagine a vertical wall on a flat piece of ground. Sunlight hits the wall and ground at a 45 degree angle, lighting each equally. But look closer and you see both surfaces appear darker closer to where they meet. This is because every time light bounces off of a surface some of it gets absorbed. Any light that hits close to the 90 degree join tends to bounce back and forth more times between the two surfaces before it reaches the observer's eyes and so more of it is lost.

What I am going to do here is attempt to reproduce this effect on the skin by adding shadows wherever the shape of the aircraft would absorb some of the light hitting it. The technical term for this is ambient occlusion and while 3D art programs like Substance Painter can use the shape's geometry to generate an ambient occlusion map automatically, the shape data needed for this is not available to AH skinners. So for this skin I am going to have to do it the hard way.

Hinge line shadows

First of all I will add some shadows for the control surface hinge lines. The leading edges of movable control surfaces need some clearance from the fixed surfaces they are hinged to. This allow for up and down movement and this gap creates a shaded area just behind the hinge line. While later AH plane shapes have these gaps represented in 3D, the P-38 doesn't. Creating shadows here should make for a worthwhile illusion of a hinged surface and it isn't very hard to do.

First I create a layer called “Hinge line shadows” and put this into a new layer group called “Shadows”, a copy of the opacity mask layer goes in here as well, at the top of the group stack. The method I use for these shadows is as follows, the screenshots below should aid in understanding it.

Looking at photos of P-38s shows that their hinge lines were quite tightly fitted. So as I don't need very wide shadows I select a one pixel wide line tool using red for clarity. Using this I draw a vertical line near the hinge line of an aileron and a bit longer than it. Next I do a 1 pixel wide Gaussian blur on this line. What I eventually want here is a blurred line, but only on the aileron side of the hinge line. So using a box selection tool I select the left half of the blurred line and delete it.

Now I need to rotate this line to match the angle of the aileron hinge line. To find the angle I select the line tool and set its width to 0 pixels. Then I draw exactly over the hinge line making a note of the angle PSP displays for this non-existent line. I copy and paste my hinge line, rotate it to the angle needed, position it over the hinge line and delete any excess length off the top and bottom. This line is then pasted to the other aileron hinge lines. The non-rotated line is pasted to the elevator and rudders, with gaps in the rudder lines to allow for the balance weights and elevator clearance the real rudders had. Then its just a matter of turning the lines black and adjusting the layer opacity as needed.




Wing and tail joint shadows

Next I will create shading at the places the wings and tail meet the fuselage pod and booms. This is tricky because it means adding shadows onto two or more UVs in such a way that where the UVs meet one shadow is not bigger or more powerful than an adjacent one, as this would emphasis the UV seam which is not a good thing. The method I use to avoid this is as follows.

So to start with I create a new layer in the shadow group called “Wing and tail shadows”. On this layer I paint the carefully-edited red and blue areas shown in the screenshot below. The close ups of the top outer wing to boom joint shows the process.

The top left shot shows the basic shadow shapes, using red and blue for these makes the position of the UV joint clear. What I am trying to achieve here is to visually have the same amount of red above the joint as there is blue below it. If the depth of red and blue matches either side of the seam the resultant shadows should match too, without one being darker than the other. Because of UV scaling it is not necessarily the case that these red and blue areas will be the same depth on the bmp, it is how they look in the viewer that counts. I also make sure the depth of blue on the wing matches for the top and bottom wing UVs where they join at the leading edge.

Note how the shapes get narrower at the trailing edge and again at the thickest part of the wing. This is because less light would get trapped in these places. Light could bounce off behind the wing at the rear and the boom is less vertical at the point where the wing is thickest which again means less light trapped.

The top right close up shows the red and blue shapes once a 10 pixel Gaussian blur has been applied to them. This has caused a problem in this instance as the shadow has wrapped too far across to the centre line of the boom. The convex surface on top of the boom wouldn't trap any light so I don't want the shadows to go this far. Carefully in stages I lower the shadow in height, while still keeping a blurred top edge, until I get the result in the lower left close up shot.

The bottom right close up shows the shadow once it is turned black and reduced in opacity. The effect should be fairly subtle and not leap out at the you.

There is a danger when blurring the shapes that the blur will expand onto UVs where it is not wanted. For example on the two middle boom UVs the red could blur all over the spinner UV placed just behind them. To prevent this I do the blurs a few at a time rather than all at once. Moving to my “Olive drab” UV layer, I carefully select only those UVs I want to blur, move back to the “Wing and Tail shadows” layer and then do the Gaussian blur. This restricts the blurring to the UVs selected. Before I repeat the process I check the results in the viewer, looking for issues such as the stretching problem on the top of the booms.

Once the shadows are all blurred and edited as required I turn them black and adjust the layer opacity as needed.




Other shadows

There are some other places on the P-38 which would benefit from some ambient occlusion and for these I create a new layer I call “Shadows”. The before and after screenshots below show the effect. For these I have turned the viewer's directional lighting off to show the effect more.
On the upper wing tips there are two small vents that exit the intercooler air and on the front undersides of the booms are air exits for the oil coolers. By adding shadows to these vents it gives a fairly convincing 3D effect.

The air intakes on the outside of each boom below the wings are given some shading, both on the scoops themselves and on the booms and lower wing surfaces close to them. Also shading is added to the bomb pylons where they meet the lower wing.

In all cases the process is the same as before, create a shape, check it in the viewer, edit as needed, blur it and then again edit as needed. This method gives a lot more control than trying to use something like an airbrush tool.

Finally the booms where they are covered by the radiator pods receive some shadows. The shots of the radiator pod again show the process. I create a black rectangle and erase two round areas that match the front and rear of the pods when seen in the viewer. Then I blur the shape before carefully erasing the shadow above and below the pod. Ideally I'd like to have added a little shading above and below the pods as well but texture stretching on the pods prevented that.







That's it for now. Next time I will make some improvement to the default textures for the smaller items on the skin, like the gear, wheels and internal bays.

[Greebo]

Part 5: Improving the remaining default parts and adding the paint scheme

Improving the default parts

To save time skinning what is a very old P-38 shape I've decided not to recreate all the small items like gear, gear bays, turbochargers etc. Most of these are either good enough or are not going to easily be seen by anyone. However many of these parts can be improved without much effort and there are a few more visible items I do want to redo.

I create a new group called “Small parts” and put the “Small parts UVs” layer I created early in the build inside it. What I want to do first is isolate all the small part UVs that are on the default skin and put them onto this layer. To do this I use the selection tool to select everything that is on the “Small parts UVs” layer, then with these areas still selected I move to the default skin layer and press CTRL C to copy them. Next I move back to my new “Small parts UVs” layer and press CTRL V to paste everything from the default skin layer that was in the selected zones onto this layer, lining them up over the blue UVs.

The first thing I want to do with these parts is to make some of them darker. The aluminium and silver painted default parts such as the gear and gear bays look far too light to me, so selecting just these parts I adjust their brightness to a level I am happy with. I do the same with the internal cockpit parts and also the turbocharger parts, which I desaturate a bit as well. I then clean up some of the shadows on the gear parts with an airbrush tool.

Next I create a new “Small parts shadows” layer and draw some thick black lines along the top and side edges of all the gear bay parts. Selecting these parts in the “Small parts UVs” layer I move back to the small parts shadows layer and do a Gaussian blur on these lines to create some shadows for these parts. I also create new radiator and oil cooler textures and shadow them in the same way.

Although wheel covers were often removed on P-38s my skin's going to have its wheel covers fitted and will also have a diamond tread pattern on the tyres, so the original wheel and tyre texture has to go. My new wheels start as three circles and a rectangle, the inner circle is a painted cover, the middle is the metal rim and the outer one and the rectangle are the tyre. With these parts covering the default textures I create some fasteners, rim lines and a diamond tyre tread. The later needs tweaking a bit to get the tread to line up properly in the viewer. The tyre and metal parts go onto new layers created for those materials in the paint and materials group, the cover goes into the olive drab layer and the panel lines, tyre tread and wheel rim into various panel line group layers. Eventually all these layers will get different treatment in the lighting and normal files so its important to think about what goes where.

One other item I decide to reskin is the texture of the inside of the wing where it is exposed when the flaps are dropped. Although its unlikely anyone will ever notice this its just bugging me that the standard texture looks nothing like the real aircraft. To make the new part I paint over these areas in light grey on my bare metal layer. Then I create a mask in red of the raised structure I want on a test layer, copy and paste this mask data onto the small parts shadows layer, turn it black and Gaussian blur it a couple of pixels. Then I reselect the mask on the test layer, go back to the shadows layer and hit delete. This just leaves the blurred edges of black that surround the mask and this gives a pretty good raised structure illusion.

The screenshots below show before and after shots of the small parts and some of the processes used to alter them.







The paint scheme

Now I am going to paint the camouflage and markings for this skin. I have been asked to skin a P-38G from the 347th FG, 339th FS based in the Solomons in 1943. It will be used in a Yamamoto intercept scenario to be run in November, along with appropriate G4M1 and A6M3 skins that I have yet to do. My go to researcher Lyric1 has found me some good info on all these aircraft. However for the P-38G I decided to base my skin on a photo of aircraft 129 that I found in the book “The Lockheed P-38” by Warren M Bodie, there were also some photos of it here on the Pacific Wrecks site. I went for this one because the book photo is better quality and more complete than the other 339th photos found on the web, the aircraft has some personal art and kill markings, the pilot is a decorated ace and there's a good story attached to him, which I'll add at the end of the build.

Another useful source I found on the web is the decal and paint guides found in this Modelling News review for the new Tamiya P-38F/G plastic kit. This not only shows the entire camouflage scheme and markings placement for a similar aircraft but also where to put all the maintenance signage. It also showed up a few minor errors in my panel lines that I have since corrected.

So first of all I go to my “Olive drab” layer and change the colour of everything on it to olive drab. Then I duplicate this layer, rename it ”Neutral grey” and turn everything on it to this colour. Using a selection tool I roughly select any area that should be olive drab (tops of the wings, upper half of the booms etc.) and hit delete and then check the results in the viewer. Using photos and the Tamiya guide as reference I then carefully edit the join lines between the olive drab and neutral grey on the pod and booms with eraser and airbrush tools.

I also move the join line down on the wing and tail leading edges. Having a bit of olive drab on the lower wing leading edge allows for a blurred rather than sharp transition and also hides the UV join much better. The problem with doing this is the front of the lower wing UV is stretched which causes ugly artifacts to form there. Its just a question of nudging the borer back a pixel at a time until these disappear. With all the grey borders done I do a 1 pixel blur on them as the photo shows a fairly soft border.

With the grey is done I create a USAAF markings layer and start on these markings, which are simple star and circle shapes that PSP can create for me. On a “339th FS markings” layer the “129” is drawn from vertical, horizontal and 45 degree lines using the panel lines on the photo as a size guide. I never use the program's text tool to create this sort of marking, its always a lot more accurate to do it by hand. The kill marks are just slightly pink 3 by 5 pixel rectangles with an off centre red dot applied.

For the personal art “Oriole” written on the outer cowlings I decide to paste part of the photo directly into the skin for reference. Loading a scanned copy of the photo into PSP I crop it to show just the cowling, draw red lines over all the panel lines and then paste it as a new “Photo” layer into the working file. With this photo shrunk to roughly the same size as the skin cowling most of the panel lines on it would normally be blurred into invisibility. However with them drawn in red they still show up. I use these lines to edit the photo so the red lines on the cowl panel the art is drawn on match the lines on my skin. What I use to do this are a mixture of the rotate, resize, skew and horizontal and vertical perspective tools included in PSP. With the photo edited to match the skin I can use the image of the “Oriole” text as a guide to draw this in red on the marking layer. Once happy I turn it white and copy and paste it to the other cowl.

After that I create a “Maintenance signs” layer and add all the little “No Step” and fuel filler signs that tend to cover military aircraft. I put the red bits on their own layer as it makes things easier to edit that way.







That's it for this time, next is the weathering.

[Greebo]

Part 6:  Weathering

Noise effect and stretching mask

So what I want to do now is to turn my P-38 skin into something that looks like its been in a war zone rather than an air show.  The 347th FG operated from Guadalcanal and other forward bases in the Solomons so its P-38Gs got quite dirty.

The first thing I am going to do is to add a noise layer. This is very easy to do, will age the paint surface a little and will allow me to illustrate an issue I am going to have weathering this shape. To do this I make duplicates of my olive drab and small parts UV layers, merge them into one layer I call “Noise” and turn everything on them grey. This layer goes into a group called “Weathering” which sits just above the “Paints and materials” group but below all the other groups. On my noise layer I select everything and use the “Add noise” command in PSP to create lots of randomly-placed multi coloured dots all over the skin and then delete the grey base colour selected with a colour picking tool.

Eventually I will turn the noise layer down until the dots will almost disappear but for now look at the top left screenshot below to see how the effect looks with the layer at full opacity. What bothers me is the transverse stretching on the top of  the booms and pods and also the mismatch of seams between the left and right UVs. I have been careful so far not to only add detail to these areas that wraps transversely across the skin but now I want to add splotchy dirt layers over the whole surface whose tone variation will show up this stretching as well as the L/R UV seams. I can't get round this problem entirely but I can mitigate it a bit by creating an opacity mask.

 This is the same idea as the scaling mask I created for the panel lines. Where the mask is white it has no effect and where it is black it erases everything from the layers below it in the group's stack, grey tones give a partial erasure. So using the stretched dots as a guide mask I create a mask layer with black areas covering the tops and bottoms of the booms, pod, rad ducts and air intakes, as well as the tip of the bomb pylons and the leading edges of the lower wings, as in the top right screenshot. When I place this mask just above the noise layer and set the layer to 50% opacity it gives the effect in the  bottom left screenshot. Here the dots on the stretched areas have been reduced in opacity but not removed completely. Once the weathering is done I will tune the mask's opacity to get a trade off between hiding the stretching and seams while not seeing visibly less dirt in those areas compared to the rest of the skin. The bottom right shot shows the noise effect at 3% opacity which gives a slightly grainy and aged appearance to the skin.



General dirt effects

Next thing I am going to do is add a couple of subtle grime layers and I can do this very quickly by using the mask you can see in the lower right screenshot above. This mask is one I created myself a couple of years ago and that I now paste into all my skins for creating variation in weathering layers. However many art programs include similar masks and there may be something suitable in yours that you can use. It essentially just needs to have a random subtly changing variation in tone giving a cloudy or dirty appearance and ideally without too much repetition.

I make a new layer placed below the stretching mask called “Dirt, dark brown” and flood fill it with that colour. Then I add my dirt mask and reduce the dark brown layer's opacity to get the level of grime I want. Next I duplicate this layer and its mask, rename the duplicate “Dirt, light brown”, flood fill the new layer with light brown and then rotate its mask 90 degrees. Rotating the mask moves all the tone variations on it around so in some places the light brown and the dark brown masks will both be white or black and in other places opposite shades. This combination of masks and colours creates a random non-repeating set of dark and light brown splotches all over the skin. This dirt effect needs to be kept subtle or it shows up UV seams too much, the stretching mask I created earlier helps here though.

Another easy effect is panel line dirt which represents the grime that collects around panel edges and other imperfections in the surface. For this I make a duplicate of the whole panel line group, call it “Panel line dirt” and move the group into the weathering group. Then I Gaussian blur the panel lines in each layer by a few pixels and adjust the layer opacities within the group to get a good balance. To make these blurred lines look more like dirt I add a copy of my dirt mask to the top of the group. This mask makes the blurred lines appear more gritty and varied.

The dirt mask is also employed in the paints and materials group. This time I paste it into an adjustment layer for saturation and lightness. Setting this adjustment layer to reduce both saturation and increase lightness makes the paint seem more faded and old, in some places more than others.

The last of the quick-to-do weathering layers I am going to create is for worn rivets. This represents where paint has chipped off individual rivets. For this I make a duplicate of the rivet layer called “Worn rivets”, move it to the weathering group and turn these rivets light grey. Then I use an eraser tool sized to cover the whole skin with 100% hardness, 50% density and 100% opacity. Clicking this onto the layer once removes half the rivets in a random pattern. I then repeat this a few times but at lower opacities, which creates some variation in rivet visibility.

You can see the effect of these dirt, nose, paint fade and rivet layers in the before and after screenshots below. Apart form the stretched areas mask all these effects took me less time to create than it took to write about them here, as it was mainly a question of copying and pasting stuff I had already done and telling PSP to do some simple conversions to the data.



Specific dirt effects

Although globally-applied dirt effects have taken me along way to making the plane look dirty in a short amount of time in reality real planes get dirtier in some places more than others. Exhausts and guns create stains, mechanics spill fluids, paint gets chipped, mud gets applied by the wheels, props and people and so on. To recreate these effects I am going to have to do some actual painting.

I'm going to start with the heat and exhaust stains. Looking at photos of wartime P-38s it seems the exhaust gas on a P-38 exits behind the turbochargers and over time creates dark stains on the upper vertical tails with a little on the tops of the booms. Around the turbochargers themselves a light pinkish stain is often very noticeable. This seems to extend forward of the exhaust outlet so I assume this is down to heat discolouring the paint and metal as much as lead deposits from the fuel.

So I create two new layers for “Heat stains” and “Exhaust stains” so I can later edit the opacity or colour of each effect independently. These go above the stretching mask layer in the weathering stack as I do not want these layers to be altered by this mask. These stains are sprayed on in red on one half of a boom and a vertical tail. Some careful editing of the stains on top of the booms is needed due to the large amount of vertical stretching of the texture here. The result is not ideal but it isn't too bad given the limitations of this old shape. Once I am happy with the results I paste these stains wherever else they are needed making sure everything lines up left to right. Then I change the colours from red and alter both layers' opacity as per the screenshot below.

Looking at photos of  347th FG P-38Gs most, including the one I am skinning, show dark lines to either side of the panel lines on their noses. My take on this is that their aircraft were most likely shipped across the sea on the deck of a carrier, that to prevent corrosion the panel gaps were all covered over by glued-on strips of material and that the lines are the residue of this glue. So for this effect, I draw these lines on a new layer and add a copy of my dirt mask to make the lines appear suitably inconsistent.

I paint my tyres and a few other likely places on the skin with some brown to simulate mud.

Next thing to do is the metal paint chips. To create the chips its just a question of painting light grey shapes over the skin in appropriate places, using photos as a reference. The photos I have of this plane only show the nose with out much chipping but other photos from this group, as well as of other P-38s, show chips on the leading edges of the wings and large areas of wear above the wings from foot traffic to either side of the cockpit.

I am also going to apply many tiny chips on the edges of hatches to simulate knocks from when they were removed. As I don't want the chips to sit actually on the panel lines but a pixel or two either side I create a mask to prevent this happening. This mask is made from a duplicate of my panel line group, I adjust all the layer sliders in this new group to 100% opacity, add a white fill layer at the bottom of the group's layer stack and then merge all the layers. Then I paste this data into an opacity mask attached to my paint chip layer. This mask will now erase any part of a paint chip that lies directly over a panel line saving me a lot of time editing this by hand.

I am also going to simulate some areas where the camouflage paint has worn down, not all the way to the metal, but just to the yellow/green primer it was painted over. The basis of this effect is the metal paint chip layer. I duplicate this, turn the chips yellow/green and then Gaussian blur the whole layer. This creates a fuzzy yellow border to my metal chips which looks far too regular and artificial to be realistic. So to break up the yellow I add a copy of my dirt mask to this layer too. To further enhance the effect I paint some other areas with the yellow, mainly places ground crew would have walked.

The last thing I am doing to this file to weather the P-38G is to create a few dark stains layers for things like dirt streaks, oil stains and drips. These stain are painted on by hand with a bit of help from copy and paste. I also use them to break up the regularity of the panel line dirt layer a bit more by applying extra stains here and there over the panel lines. I use photos for reference but also try to imagine where dirt would form. Oil spills would be mostly around the engine hatches, dirt streaks form behind and obstruction to the airflow like the bomb pylons and so on. This is another layer I use the dirt mask on.

The before and after screenshots below some show these effects in isolation while the final one is an overall progress shot. The diffuse file is done for now, although I'll likely do some final tinkering once the lighting effects are added. Next time I will create the bump effects in the normal map.

[Nefarious]

Coming along nicely!

[Greebo]

Part 7: Normal Map

In this part of the build I am going to make a normal map for my skin, which is a map that represents artificial bumps and dips on the surface of the 3D shape. The game reads this map's height variation data and uses it to place shadows and highlights on the shape's surface based on the relative position of the sun.

Rather than start from scratch I am going to use my existing diffuse map's working file “p38g1.pspimage” to get most of the data. So I create a duplicate of this file and rename it “p38g1_n.pspimage”. With this new working file open I start deleting the layers I don't need. This includes most of the colour scheme layers, although I rename the olive drab layer “Base height” and turn it mid grey (RGB 128/128/128). This shade is in the centre of the 256 shades of grey available in this map and I'd suggest you always use it as the base for a normal map as any other shade can cause issues related to UV reversal. In this map any shade of grey darker than this will represent a dip and any lighter shade a bump. Other things that go are all the weathering layers and almost all the shadow layers. I keep the “Hinge line shadows” layer as I want to use it to emphasis the control surface gaps in this map. On more modern AH shapes which have hinge gaps as part of the 3D geometry then this would go too.

What I end up with is shown in the top left screenshot below. This consists of the background and base height layers at the bottom of the stack, the panel line and fastener layers above that and the hinge line shadows, some holes and other detail at the top. Most of this data was black in the diffuse map and so needed no alteration for this map as it is going to represent dips in the surface. The navigation lights though I changed to white as these stick out above the surface of the real P-38.



Viewing the normal map in the viewer

Before I go any further I want to see what this map looks like in the skin viewer. So I save the file as a bmp and then reload this saved bmp back into Paint Shop Pro. In order to convert my map into a format that the viewer (and game) can read I use a free normal map generator add on for Paint Shop Pro that I got off Nvidia's website. There are similar free add-ons available on the web for other paint programs like Gimp and Photoshop. The default settings for this add-on are left alone except for “Scale” which I set to 3 and “Invert Y” which I tick. Applying this add-on to my bmp I get the purple map shown in the top right screenshot above.

After saving this modified bmp again I open the skin viewer to view the effect as seen in the lower screenshots. In order to see only the normal map data I have selected the “Lighting only” option in the viewer which disables the diffuse map's colour data leaving the surface a uniform light grey colour.

Coping with UV reversal

On the lower screenshots above the panel lines, fasteners and tyre tread now have a depth created by the highlights and shadows generated from the normal map's bump data. However the right hand image also reveals an issue I have been expecting since I started this build. The panel lines and fasteners on the radiator pod are reversed, they appear to be raised from the surface rather than sunk into it. This is because HTC's artist (probably Superfly) reversed the radiator pods UVs horizontally when he laid out the texture, something that he also did on the inner tail booms.

On the diffuse map this sort of UV reversal is a minor irritation, it just means that text and other markings need to also be reversed horizontally by the skinner on these UVs to compensate, but on the normal map this is much more of a problem. Since these UVs are only reversed in one axis on the bmp then this bump reversal also occurs in only one axis when viewed in the game or viewer. If the skin viewer had a slider to let me move its lighting source towards the front or rear of the plane I'd be able to show you that the left/right lighting on the vertical panel lines on these reversed parts is actually working correctly, in the same direction as the bumps on the rest of the aircraft. This is a pain because it means that simply changing the panel lines' colour on the reversed UVs from black to white won't work. The bump mapping would work correctly in the up/down axis but it would now be reversed in the left/right axis.

So this problem can't be entirely fixed, but it can be made less obvious. For most AH planes that exhibit this problem reversing the shades on the reversed parts is what I do. This is because what I am more interested in is what the skin looks like when viewed from outside or in a screenshot. Having the bump mapping look correct in the vertical axis is more important to me visually than it looking correct in the horizontal axis as the lighting source (the sun) will tend to be offset vertically more than horizontally most of the time. Also the UV that is most commonly reversed on Superfly's skins is one half of the fuselage and as not a lot of this can be seen from the cockpit the player tends not to notice it.

The way I usually do this reversal in PSP is with an invert mask. On the opacity masks I have used previously data below the mask's black areas were made transparent with that below white areas unaffected. On an invert mask data below white areas is unaffected but that below black areas is inverted, so in this case black lines become white and so on. The nice thing about using a mask for this is that it reverses the data for all the layers below it so I don't have to go into each layer and change the affected areas by hand.

On the AH P-38 though I decided on a different approach to this problem because the reversed inner booms and pods are very visible to the pilot whenever he looks left, right or backwards from the cockpit. So whether or not I apply an invert mask to the reversed areas then in-game all the bump shadows and highlights on these areas will be incorrectly aligned in either the vertical or the horizontal axis and will look weird to the pilot as the plane turns, climbs or dives. The reversed bump effects will also contrast sharply with the correctly-orientated bump effects on the wings and tail.

 So rather than an use invert mask I create an opacity mask to erase all the data for the reversed UV areas. This mask is placed in my panel line group above all the fastener layers so they are no longer visible as bumps. The panel line layers though are kept above this mask so they are. Then I carefully change the shade of only the horizontal panel lines on the reversed UVs to white. The idea is that every panel line will still cast reversed shadows and highlights in one axis but the reversed effect will only be one pixel wide and so isn't noticeable. Each line's long axis now casts the correct shadows and highlights which overpower the tiny wrong ones. This trick won't work for the fasteners though which is why I placed them below the mask. The difference between the mapping on one of the un-reversed outer tail boom sides and the reversed inner tail boom side and radiator pods above it can be seen in the top left screenshot below.



Creating raised areas

Other than the opacity mask everything I have put into the normal map so far has been taken straight from my diffuse map, at worst I have had to change a few colours on existing data. Now I could leave it like this and it would be fine but there are a couple more effects I like to add to my normal maps which I will describe now.

I like to recreate raised areas on the surface of the airframe such as the fairings that are used to blend the flying surfaces to the fuselage. On most planes these are a curved piece of aluminium screwed onto the side of the fuselage on one edge and the wing or tail on the other. I like to use the normal map to recreate the raised edges this fairing creates.

Now when I originally drew the panel lines in the diffuse map I created a separate “Raised panel lines” layer in white which represented the highlighted edges of these raised areas and what I usually do is to use this layer to create the raised areas in the normal map. I extend the white lines into boxes that cover the areas the fairings occupy and then flood fill these boxes in white. After reducing the layer opacity these then give me a nice stepped edge where the fairing starts.

There is a problem with using this method on the P-38 though. The boom to wing and tail fairings on the real P-38 do not sit above the surface of the boom itself, Lockheed butt jointed the fairing to adjacent hatches. The fairings do have raised edges on the wing and tail though. In theory I could recreate this effect with a fairing that fades from white on the wing/tail to nothing on the boom but in practice it is going to be very tough to get this to blend seamlessly across UVs and the texture reversal on the booms will screw it up anyway. So what I do instead is to paint the whole non-fairing parts of the wings and tail in black on a  “Sunken areas” layer and then reduce the opacity of this layer. I do use the raised panel lines layer to create lighter raised fairings on the fuselage to wing joint and on a couple of other places on the skin. The sunken and raised areas on the skin can be seen on the top right screenshot above.

Finishing the map

Another thing I like to do is create a slightly uneven surface to represent the way the aluminium skin is distorted by the frame below it. This is a fairly subtle effect, I use it to break up the highlights shining on the skin, making the skin surface look a little less perfect. To do this I take my rivet layer, turn the rivets white and Gaussian blur them a few pixels. I usually copy and paste this layer a few times and them merge all the copies which strengthens the effect. I also use a blurred copy of the fastener layers to make depressions around the fasteners. A copy of the opacity mask is added above these layers to erase their effects on the reversed UVs though. The lower two screenshots above show the final normal map pre and post conversion. This has the blurred rivet and fastener effects added.

So that's pretty much it for the normal map although I checked the bump levels in the game a few times and edited them by changing the layer opacity levels. This is one thing that can't be done well in the viewer as you need to see how the bumps react from the pilot's POV as the plane manoeuvrers. The lower two screenshots show the finished normal map both with and without the diffuse map. The normal effects are pretty subtle at this distance but appear more powerful when viewed close up from the cockpit.

Next time I'll finish this build log off by adding the specular, environment and power maps.

[Greebo]

Part 8: The Specular, Power and Environment Maps

The specular, power and environment maps all affect the way the surface of the skin reflects light. On the specular map lighter areas reflect more light from the sun, on the power map lighter areas have sharper, more concentrated reflections and on the environment map lighter areas reflect more of the environment around the plane. For the most part these three maps tend to look very similar to each other as shiny surfaces tend to be lighter in all three maps and matt surfaces darker.

It is important to realise that a light colour can be dark on these maps and vice versa. For example the USAAF sometimes painted their night flying aircraft in a shiny gloss black paint called Jet black  whereas the white paint on a USAAF star insignia had a duller matt or satin finish. So on the specular, power and environment maps the white paint ought to be given a darker shade than the black paint because a glossy finish will absorb less light and produce sharper and more powerful reflections. Its just a question of thinking “how shiny or dull would this be?” rather than “how dark or light would this be?”

The Specular Map

As with the normal map my starting point for these maps is my diffuse map working file “p38g1.pspimage”. I make another copy of this file and rename it “p38g1_s.pspimage” as this will become my specular map. My first job is to use PSP's “Greyscale” command to transform it from a 24-bit colour file to a greyscale file with just 256 shades of grey as this is the format the specular, power and environment files use in the game.

So what I have now is a greyscale version of my colour diffuse file. You can see what this looks like in the top left screenshot below, it is like you are viewing the file on an old black and white TV. There are a few problems with simply using this as my specular map though. The first is that all the various colours of paint on the real aircraft all had a similar satin finish and so would have reflected light to a similar degree. However on our current file all this paint is of differing shades, the white parts of the USAAF markings would end up looking a lot shinier than the blue parts for example.

To improve the file the next thing I do is to turn my background layer black by reducing its brightness to nothing. Then in my “Paints and materials” folder I delete all the layers except for the base “olive drab” layer and those layers that represent materials rather than paint, such as shiny metal or rubber. The olive drab paint layer is turned white and then has its layer opacity reduced to 30%, which from experience I have found is a good starting point for this sort of paint finish. I prefer this method of turning the data in each layer in the stack black or white and then using the  layer's opacity to alter the shade as its a lot easier to tweak this later than if I turned the data to the shade of grey I want and keeping the layer opacity at 100%.

So the rest of the file I just go up the layer stack from bottom to top and for each layer either delete it if its not needed or turn its data black or white, altering the layer's opacity to get the shade of grey I want. The bare metal and glass ends up as a light shade, the rubber and panel lines dark, most of the weathering dark except the paint chips which are light, while holes and shadows remain dark. The top right screenshot below shows the finished specular map.

Creating the spec map took me less than an hour. This is because I had planned ahead when making my diffuse file and separated anything with a different finish into its own layer. Now if for example I had put both my rubber and shiny metal parts onto a single layer on the diffuse file I would have then had to take the time to either separate that data out into two layers or alter the colour of some of the parts on that layer for the specular map. Its all about working smarter rather than harder.

The Environment Map

To create the environment map I make a copy of the specular map working file and rename it “p38g1_e.pspimage”. The only change needed for this file is to alter the base olive drab layer opacity from 30% to 10%. The environment mapping in AH looks odd to my eyes, way too sharp and highly focused so I like to turn it down to a low level by making the file dark. The lower left screenshot below shows the finished environment map.

The Power Map

The power map is another copy of the specular map renamed “p38g1_p.pspimage”. I turn the olive drab layer down to 10% on this as well so the solar reflections on the painted areas appear less focused. I also tweak some other layer opacities up or down as needed. All the shadow layers are deleted from the stack as well as ambient occlusion might affect the amount of light that is reflected but not how focused that light is.

One final thing I do to the power map is to give all the panel line layers a sharp edge reflection to either side. To do this I make a copy of the panel line group, merge all the layers inside it except the raised panel edges layer into a single layer. I rename this layer “Panel lines merged”.  Then I duplicate this layer, name it “Panel line edges”, turn the lines white and copy and paste these lines back into the layer four times offsetting the lines one pixel in each direction, effectively turning the lines from one to three pixels wide. Finally I select all the lines in the panel lines merged layer, move to the panel lines edges layer and hit “delete”. This removes the centre pixel of all the three pixel wide lines, leaving me with white borders to all my panel lines. The lower right screenshot below shows the power map.



Tweaking

With all my maps done I save them as bmps so I can view the results in the viewer and the game. It is necessary to see how the effects look in the game from the pilot's seat as the plane manoeuvrers and the lighting effects shift around on the skin. With a brand new template like this there is always a fair bit of tweaking to do with layer opacities until it looks right. Subsequent skins won't need as much unless they have a totally different scheme, i.e. a natural metal finish.

In order to submit the skin to HTC I need to do one more thing to the files. For some reason HTC require the normal and diffuse maps to be submitted as 32-bit bmps although to my knowledge they've never used the alpha channel this adds to the file. Unfortunately a limitation of Paint Shop Pro is that it can only save bmps in 24-bit format. To fix this I have to load the two 24-bit files into either Gimp or Photoshop and re-save them from there in 32-bit format. I also take a screenshot of the skin and prepare a photo of the real plane to add to the submission.

The final screenshots show how the skin looks with all the lighting maps applied, both in “Lighting only” mode and in “All lighting” in the viewer and in the game from inside and outside the cockpit. The “Lighting Only” shot is not much different to the version with just the normal map added but the panel lines are now a bit more visible where they cross the highlighted reflections and the cockpit screenshot shows how this sort of effect looks from the pilot's seat.

That's it for this build. I hope its been instructive to someone. Bear in mind that many of the issues I have encountered with the P-38G are down to it being such an old shape, the later AH planes are a lot nicer to skin than this one.