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Revert "- eliminate an unexpected slow path in the fragment shader."
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This reverts commit cd5aa65.

This does not work as expected, needs more investigation.
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@coelckers
coelckers committed Aug 9, 2021
1 parent cd5aa65 commit 39513cf
Showing 1 changed file with 1 addition and 1 deletion.
2 changes: 1 addition & 1 deletion wadsrc/static/shaders/glsl/main.fp
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Expand Up @@ -595,7 +595,7 @@ vec4 getLightColor(Material material, float fogdist, float fogfactor)
{
vec4 color = vColor;

if ((uPalLightLevels >> 16) >= 5) // gl_lightmode >= 5 are software lighting modes.
if (uLightLevel >= 0.0)
{
float newlightlevel = 1.0 - R_DoomLightingEquation(uLightLevel);
color.rgb *= newlightlevel;
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2 comments on commit 39513cf

@Talon1024
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Shaders have to run in constant time, so every code path is executed, and the results are discarded if the conditions are not met. It's best to avoid "if"s as much as possible when writing shaders.

@coelckers
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@coelckers coelckers commented on 39513cf Aug 10, 2021 •
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That's absolutely not correct with modern hardware anymore. If a condition is uniformly true or false the conditional path will be skipped entirely. The majority of 'if's in this shader is based on uniforms (i.e. constant per primitive and often even per scene) And this are provably faster than switching shaders depending on what path is needed.

With this one there seem to be some weird things going on. I reverted this because there's places in the code where this was causing render glitches. It also seems to be a bit random when the shader starts to hit a slow path. This is not consistent but seems to mainly depend on the lighting stuff.

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