我正在为游戏引擎编写以下片段着色器:
#version 330 core
layout (location = 0) out vec4 color;
uniform vec4 colour;
uniform vec2 light_pos;
in DATA
{
vec4 position;
vec2 uv;
float tid;
vec4 color;
} fs_in;
uniform sampler2D textures[32];
void main()
{
float intensity = 1.0 / length(fs_in.position.xy - light_pos);
vec4 texColor = fs_in.color;
if(fs_in.tid > 0.0){
int tid = int(fs_in.tid + 0.5);
texColor = texture(textures[tid], fs_in.uv);
}
color = texColor * intensity;
}
行
texColor = texture(textures[tid], fs_in.uv);
导致编译着色器时出现“GLSL 1.30及更高版本中禁止使用非常量表达式索引的采样器数组”表达式。
如果需要的话,顶点着色器是:
#version 330 core
layout (location = 0) in vec4 position;
layout (location = 1) in vec2 uv;
layout (location = 2) in float tid;
layout (location = 3) in vec4 color;
uniform mat4 pr_matrix;
uniform mat4 vw_matrix = mat4(1.0);
uniform mat4 ml_matrix = mat4(1.0);
out DATA
{
vec4 position;
vec2 uv;
float tid;
vec4 color;
} vs_out;
void main()
{
gl_Position = pr_matrix * vw_matrix * ml_matrix * position;
vs_out.position = ml_matrix * position;
vs_out.uv = uv;
vs_out.tid = tid;
vs_out.color = color;
}
在 GLSL 3.3 中,采样器数组的索引仅允许通过积分常量表达式(请参阅GLSL 3.3 规范,第 4.1.7 节)。
在更现代的版本中,从 GLSL 4.0 开始,允许通过 动态统一表达式索引采样器数组(请参阅 GLSL 4.0 规范,第 4.1.7 节)
您实际上尝试的是通过变量来索引数组,这是根本不可能的。如果这样做绝对不可避免,您可以将 2d 纹理打包到 2d 数组纹理或 3d 纹理中,并使用索引来寻址纹理的图层(或第 3 维)。
问题在于,在第
texColor = texture(textures[tid], fs_in.uv)
行中,采样器数组 texturues
被赋予了一个非常量索引。
最简单的解决方法是使用一个大的 switch 语句来替换行
texColor = texture(textures[tid], fs_in.uv)
,以便可以通过常量来评估纹理数组。例如,您可以写这样的内容:
uniform sampler2D textures[32];
void main()
{
float intensity = 1.0 / length(fs_in.position.xy - light_pos);
vec4 texColor = fs_in.color;
if(fs_in.tid > 0.0){
// texColor = texture(textures[tid], fs_in.uv)
// replace with large switch
int tid = int(fs_in.tid + 0.5);
switch (int(tid)){
case 0:
texColor = texture(textures[0], fs_in.uv);
break;
case 1:
texColor = texture(textures[1], fs_in.uv);
break;
case 2:
texColor = texture(textures[2], fs_in.uv);
break;
// repeat for all textures
}
}
color = texColor * intensity;
}
我通过使用一些代码生成克服了这个问题:
在 Javascript 中它看起来像这样:
const maxNumTextures = 32;
function makeSwitchCase (i) {
return `
case ${i}:
sum += texture2D(texturesArray[${i}], vUv);
break;
`
};
const fragmentShader = `
#define numTextures ${maxNumTextures}
uniform sampler2D baseTexture;
uniform sampler2D texturesArray[numTextures];
varying vec2 vUv;
void main() {
vec4 base = texture2D(baseTexture, vUv);
vec4 sum = vec4(0.0);
for (int i = 0; i < numTextures; ++i) {
switch(i) {
// we are not allowed to use i as index to access texture in array in current version of GLSL
${new Array(maxNumTextures)
.fill(0)
.map((_, i) => makeSwitchCase(i))
.join('')}
default: break;
}
}
gl_FragColor = base + sum;
}
`;
注意:我们在 JS 中使用 ` 来启动和停止多行字符串,并使用 ${some_value} 为模板提供值
我也有类似的问题。切换到较新的版本(准确地说是#460)对我来说有效。