I'm going to do a general basic tutorial on graphics, what they do, and how to use them. The topics we'll be covering are:
These will be some basic explanations, and I may add stuff to it later, I'll also copy and past some stuff from other posts so people can get some better ideas of how this stuff works.
- The alpha channel is a separate channel in a graphics file that allows certain things to happen. Note that not all graphics files support alpha channels (jpgs, bmps and gifs do not), nor do they work the same way all the time... :)
1) On an object that has been tagged as non-transparent (such as a car body), the alpha channel determines how much the surface will reflect light. White means that it is VERY reflective, black means that the surface is matte. Most of the time, the shades are in the gray area, but if you want something chrome or very reflective, it should be light gray or white. If you want it to be dull or matte, set the color of the alpha channel to black or dark gray.
2) On an object that has been tagged as transparent (such as windows or lights), the alpha channel determines how transparent the object is. Most of the time for windows or headlights, you want a medium to dark gray. This allows some of the underlying texture to show up, creating a 'sheen' as if looking through glass. The lighter the alpha for an area, the more it will show up. For example, if creating side windows for touring cars and you have letters or country flags that you want to be completely visible, make them white. In most cases you will not use black, as that will mean that NO underlying texture will appear. This will make headlights appear as if they have no cover over them.
3) For specular maps, the alpha channel determines how much of the spec map is applied to the main texture (see spec map to understand all of this). The lighter the color, the more the spec map will be applied to the main texture. This STILL works in conjuction with the spec map of the main texture for overall reflectivity.
See This tutorial
for examples of what an alpha channel looks like, how it appears in photoshop, and how it is used to make transparent objects.
- the bump map is used to create the illusion of raised and lowered surfaces on an object. For example, if you have a line where the fender and door meet on the car, you would want to use a bump map for that. Things like bolts, hoodpins and so on are also good places to use bump maps. Do NOT use bump maps for modeled objects (such as a 3dmodeled hood scoop). Do NOT use bump maps extravagantly...they only need to be applied to objects that are not modeled and need to have an appearance of being raised or lowered from the surrounding surface. Darker color on a bump map means the object appears lower, white is raised.
See this tutorial
for more info about bump maps.
- Spec maps are used to create a multi-textured surface using different color qualities. For example...on a chrome surface or car with a metallic or 'pearl' paintscheme, other colors appear on the surface depending on where the light is. Spec maps can be used to create this look, and the spec map's alpha channel determines how much of the color 'bleeds' through. If you create a car with a brilliant blue paintjob, but would like it to have brilliant red-purple highlights when the light hits it, you would create the base blue texture, set the main alpha channel to lighter grays (for reflectivity), then create a reddish spec map and set the alpha channel on the spec map to medium-dark gray. You don't want to overdo it too much.
Notice on this vehicle how there are lighter yellow/blue areas that appear through the paintscheme. These were done with the assistance of the spec map. If a reddish tint had been applied, you would have noticed that as well. You can also see that the surface is highly reflective. This was done using a lighter alpha channel (but NOT white). As well, you can see the cube map reflected in the paint...and bump maps have been used to show door panel lines, etc.
- cube maps are used to provide an actual 'reflection' to the surface texture of a vehicle when they are highly reflective. The actual cube map is typically a darkened image of the track, trees or whatever when used in sim racing. For doing renders, the cube can be whatever the render artist would like to have reflected in the surface.
For additional tutorials on cube maps, see here
, and here
Spec & bump maps need to be generally applied to individual car/body types. For example, you would have a spec & bump for a Ford Fusion, and one for a Chevy Monte Carlo. You CAN have a spec map for each individual car, but you have to decide how much graphics memory you can afford to use up...in a stock car series, with 40 cars on track, you just can't afford to have a spec for every single car. However, if you CAN afford it, individual spec maps for each paintscheme create an awesome effect when viewed on track. Spec maps usually don't need to be the same size as the original texture template, a 1024x spec map for a 2048x texture would work just fine.
To create the illusion of a metallic paintscheme, there are a variety of ways of doing it. I'm not sure which one works the best, so you can experiment. It may also depend on if you can provide a spec map for each car, or just for each make. Every single solution involves using grain
in the map to create the illusion. Grain is a filter that most graphics programs have, it creates a 'grainy' look to a texture.
What you can do is either A) create a grainy look to certain areas of the main alpha channel for the main texture. This would work ok if you you don't have separate spec maps for each car, and you also don't need to have a spec map the same size as the original. B) if you can provide a spec map for each car, then you can use a spec map the same size as the original paintscheme, and apply a grain to the spec alpha channel. This would serve to have metallic 'flecks' that show up with a slightly different color, giving it that iridescent effect. You could also experiment with putting a grain into the spec map itself. You don't want to have a lower sized spec map for this type of metallic effect, as the 'grain' would not look right if they were too big. You can also experiment with the contrast of the grain, as you would like to have some flecks show up bright, and some not so bright.
The game also will use the correct specular and bump maps (bumpmap in DX9 only), and alpha channel (DX8 and DX9 only). It's easy to tab in and out of the game and reload the can skin (initially create it as an alternative skin on an existing car by using a CARNAMEskins folder, then just select a different skin and re-select the desired skin to see your changes).
If you want one color to be more shiny than another, highlight that color, switch to the alpha channel (it's a grayscale image of the car), then increase the brightness of the highlighted area.
For best results, you should turn off shading and highlighting layers temporarily, then highlight the color you want to edit while "Use All Layers" is selected, so the selected area will not grab decals and panel seams etc. Otherwise you could potentially increase the shininess of decals that are supposed to be covering that painted area, or increase shininess of black lines that are supposed to be physical separations between panels (and thus should have no reflections whatsoever).
For most cars, the basic thing to do is darken the alpha channel where decals are, since decals generally should be less reflective than the sheet metal. The template's default alpha channel already has this done for the headlight/taillight stickers and the car branding stickers. However, it does not have it done for the contingency stickers, so be sure to use the Magic Wand set at 255 tolerance to grab all the contingency stickers, then switch to Alpha and darken them to nearly 0 (if not actually 0). Do the same with your sponsor decals.
For additional tutorials on textures in general, see here
, and here
Thanks to the RSR team and various other individuals for their help and assistance over the years...