Hi All,
I spent a little time this weekend looking through the Rembrandt
shader code to gain some familiarity and (naively) see if I could find
any obvious performance improvement, in particular by unwrapping
loops/if tests, as Rembrandt is just a little too slow on my machine
to be usable.
Unfortunately most of my efforts actually made things worse, often by
a factor of 2. Evidently modern GPU GLSL compilers are more advanced
than I had thought, and I should be a little more humble in the
future!
However, I did notice a couple of things I'd like to get comments on,
mainly from Fred I suspect.
1) Shaders/ssao.frag: This is the fragment shader for Ambient
Occlusion. Line 54 starts a FOR loop that only executes once. I
don't know enough about the shader to say whether it's a straight bug
and should execute 4 times, or whether it's correct and the FOR loop
can be removed. Can anyone confirm?
2) Shaders/sunlight.frag: I think I can remove the if() tests at the
end of the shader (around line 95), so
float cosAngIncidence = clamp(dot(normal, lightDir), 0.0, 1.0);
float blinnTerm = clamp( dot( halfDir, normal ), 0.0, 1.0 );
if (cosAngIncidence > 0.0)
Ispec = pow( blinnTerm, spec_emis.y * 128.0 ) * spec_emis.x *
fg_SunSpecularColor.rgb;
float matID = texture2D( color_tex, coords ).a * 255.0;
if (matID >= 254.0)
Idiff += Ispec * spec_emis.x;
can be replaced with the following code:
float blinnTerm = clamp( dot( halfDir, normal ), 0.0, 1.0 );
Ispec = step(0.0, dot(normal, lightDir)) * pow( blinnTerm,
spec_emis.y * 128.0 ) * spec_emis.x * fg_SunSpecularColor.rgb;
Idiff += step(0.996, texture2D( color_tex, coords ).a) * Ispec
* spec_emis.x; // 254: Water, 255: Ubershader
This doesn't improve the performance on my machine by a significant
amount, but it would seem worth doing.
3) From reading Effects/sunlight.eff, I don't think sunlight.frag is
ever executed with filtering == 1, (that's what
sunlight-nofiltering.frag is for), so the if() test on line 70 can be
removed.
-Stuart
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