performance - 是否应避免在着色器中使用范围和光源类型的条件？(Should conditionals for range and light type in shaders be avoided?)

Question

Similar questions:

(类似问题：)
Is this shader conditional bad for performance and can it be optimized?

(此着色器是否有条件损害性能，是否可以对其进行优化？)
Do conditional statements in shaders come at a higher cost?

(着色器中的条件语句会带来更高的成本吗？)
Do conditional statements slow down shaders?

(条件语句会减慢着色器的速度吗？)

My question is more specific.

(我的问题更具体。)

I have 3 types of lights: directional, pointlight and spotlight.

(我有3种类型的灯：定向灯，聚光灯和聚光灯。)

The latter 2 are attenuated and are limited by range.

(后者2被衰减并受范围限制。)

The first isn't.

(第一个不是。)

Pseudocode for the fragment/pixel shader:

(片段/像素着色器的伪代码：)

for each light {
    if (type == direcional) {
        color += lightColor * angleFactor;
    else {
        if (light.range < rangeToPixel) {
            // out of range - do nothing
        } else {
            atn = 1.0 / (const + lin * dist + quad * dist * dist);
            if (type == spotlight) {
                spotlightFactor = ... // a number from 0 to 1 signifying the decrease in intensity
                color += lightColor * spotlightFactor * atn * angleFactor * dot(n,l);
            } else { // pointlight
                color += lightColor * atn * dot(n,l);
            }
        }
    }
}

This looks like a lot of branching for a shader.

(对于着色器，这看起来像是很多分支。)

My thoughts are:

(我的想法是：)

1. Move the directional light computation to the vertex shader since it contributes to all pixels/fragments in the vertex equally.

   (将定向光计算移动到顶点着色器，因为它对顶点中的所有像素/片段的贡献均等。)

   This will still need an if check on the light type.

   (这将仍然需要一个if在光类型检查。)

2. Pointlight computation can be done on the spotlight branch by giving it a 360 degrees inner angle by default (then the direction of the spotlight is not important), so spotlightFactor == 1 .

   (可以通过默认为聚光灯分支设置360度内角来进行聚光灯计算（此时聚光灯的方向并不重要），因此spotlightFactor == 1 。)

   This gets rid of the branching on that computation but means that more math is being done when it is not needed, so more work.

   (这摆脱了该计算的分支，但意味着在不需要时可以完成更多的数学运算，因此需要更多的工作。)

Because I have only one system to test on, it won't be indicative, so I require help with the approach/design.

(因为我只有一个要测试的系统，所以它不是指示性的，因此我需要有关方法/设计的帮助。)

How should I modify the code?

(我应该如何修改代码？)

Using D3D9 shader model 3 and OpenGL version 2.1.

(使用D3D9着色器模型3和OpenGL版本2.1。)

  ask by user1803551 translate from so

Answer 1

等待大神答复