I was messing with Winamp visualizations just now when I stumbled on an idea to create the 3D 'fog' effect in our engines. Feel free to use this method--it's pretty darn simple.

First of all, the best way to improve FPS speed is to limit the draw distance. But...when polygons disappear after appearing in the screen for just a few seconds while moving, it looks really fake.

So! The fog effect can help obscure the disappearing polygons in the distance. Right, obvious enough.

So, here's my idea:

1. Set yourself a 3D_FogActive flag to control if fog is enabled/disabled
2. Have a 3D_FogColor icon, where FogColor is an RGB integer.

On rendering:
3. When you clear the screen, fill the screen with the fog color.
4. Proceed to draw polygons.
5. Take the maximum Z-distance displayed, and the minimum Z-distance displayed, say, 0 to 1000.
6. Interpolate 100 shades of lucency for the polgyon's distance.
IE, polgyon_fog_obscured_value = ( polgyon_z_value * 100 / (polygon max z value - polygon min z value) ) / 100

7. Set lucency to the correct degree, and draw the polgyon.

This way, polygons further in the distance are drawn more lucenctly...which means the fog color is shown, and it looks like the polygon is obscured by the fog. When polygons are almost out of vision, the lucency is very near 100, so they look very obscured.

Of course, this would probably take a lot of processing speed, so it wouldn't be perfect, but it'd be pretty neat, and you could toggle it on and off.

Quote:Originally posted by Technetium


I think it would be much easier to just adjust the color of the triangles based on their distance..

That trick is z-flat shading, which I never tried but apparently looks pretty annoying. With regards to the fog, it's an interesting idea and would probably make for a nice visual effect. I don't believe it would be much of a speed improvement though, since unless your scene is huge you're unlikely to be culling all that much.

Wait. Another idea. Basically, blit another triangle --the fog shader-- on top of the flat triangle. Blit the flat triangle normally, so it does not blend with other flats.

1. Blit the normal flat shade..
2. Then calculate z-lucency...
3. And blit the fog shading triangle (which becomes more and more intense as the distance increases, thus obscuring more and more of the flat).

This way...every flat triangle is not actually blitted lucent, so flats on top of flats don't blend into each other, yet are still tinted with the fog shade.

However, this would be theoretically even slower, since instead of blitting a lucent triangle, you are blitting a flat and a lucent triangle. Still, I think the visual result would be exactly what we would want.



EDIT: Technetium's idea of recalculating the triangle color would probably be faster, but it wouldn't work for a texture/distorted primitive, and it might be difficult if you also include your flat shade lighting calculations in that same color.

In fact, this could probably be done with the CalcColor function Vecna made. In fact, that could be better. Either approach would work, Technetium's is faster but maybe less flexible.