GLSL：采样器上传仅在删除未使用的采样器时有效

Question

我目前正在尝试在OpenGL中使用framebuffers实现延迟着色。帧缓冲区本身工作得很好，但是当我在着色器中不使用所有统一采样器时，其中一个纹理就会停止工作。

这是我的片段着色器，帧缓冲的测试演示：

#version 330 core

uniform sampler2D texCoordTex;
uniform usampler2D texIndexTex;
uniform sampler2D normalTex;
uniform sampler2D positionTex;
uniform sampler2D depthTex;

float linearizeDepth(float depth){
    float n = 0.1, f = 2000;
    return (2*n)/(f + n - depth*(f-n));
}

out vec4 out_Color;

uniform sampler2DArray texArray;

void main(){
    ivec2 texelCoord = ivec2(gl_FragCoord.xy);
    vec2 texCoord = texelFetch(texCoordTex,texelCoord,0).xy;
    uint texIndex = texelFetch(texIndexTex,texelCoord,0).x;
    vec3 normal = texelFetch(normalTex,texelCoord,0).xyz;
    //vec3 pos = texelFetch(positionTex,texelCoord,0).xyz;
    float depth = linearizeDepth(texelFetch(depthTex,texelCoord,0).x);

    out_Color = vec4(0,0,0,1);

    if(texelCoord.x < 512){
        if(texelCoord.y < 300){
            out_Color.xyz = 0.5*normal+0.5;     
        }else{
            out_Color.xyz = vec3(texCoord,texIndex/50.0);       
        }
    }else{
        if(texelCoord.y < 300){
            out_Color.xyz = texture(texArray,vec3(texCoord,texIndex)).xyz;      
        }else{
            out_Color.xyz = vec3(depth);        
        }
    }
}

请注意，未使用的行vec3 pos = texelFetch(positionTex,texelCoord,0).xyz;已被注释掉 记录采样器统一上传：

13/05/2015 15:11:24,317 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = depthTex, unit = 1] uploaded to shader.
13/05/2015 15:11:24,317 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:11:24,317 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = texCoordTex, unit = 2] uploaded to shader.
13/05/2015 15:11:24,317 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:11:24,317 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = texIndexTex, unit = 3] uploaded to shader.
13/05/2015 15:11:24,317 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:11:24,317 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = normalTex, unit = 4] uploaded to shader.
13/05/2015 15:11:24,317 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:11:24,317 WARN  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = positionTex, unit = 0] not found in shader.
13/05/2015 15:11:24,317 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:11:24,318 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = texArray, unit = 5] uploaded to shader.
13/05/2015 15:11:24,318 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE

当然找不到

positionTex，因为它没有在着色器中使用。

Sponza场景的结果图片：

如果我没有对vec3 pos = texelFetch(positionTex,texelCoord,0).xyz;行发表评论，则texCoordTex不再有效，统一上传会产生GL_INVALID_OPERATION错误。

结果如下所示，因为纹理坐标为零。

日志输出显示错误：

13/05/2015 15:20:26,162 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = depthTex, unit = 1] uploaded to shader.
13/05/2015 15:20:26,162 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:20:26,162 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = texCoordTex, unit = 2] uploaded to shader.
13/05/2015 15:20:26,162 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:20:26,162 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = texIndexTex, unit = 3] uploaded to shader.
13/05/2015 15:20:26,162 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:20:26,162 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = normalTex, unit = 4] uploaded to shader.
13/05/2015 15:20:26,162 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:20:26,162 WARN  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = positionTex, unit = 0] not found in shader.
13/05/2015 15:20:26,162 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_NONE
13/05/2015 15:20:26,162 INFO  [default] ShaderProgram::ShaderProgram: TextureUnit[ name = texArray, unit = 5] uploaded to shader.
13/05/2015 15:20:26,162 WARN  [default] ShaderProgram::ShaderProgram: glGetError() is GL_INVALID_OPERATION

我是否忽略了某些东西或者这是一个驱动程序错误？ 我使用的是ATI HD 6870，我可以在Linux和Windows上重现这种行为。

Answer 1

我发现了这个错误，它与着色器无关。在我的ShaderProgram课程中，我使用glGetActiveUniform查找有关统一变量的信息。我稍后使用统一索引作为位置，但必须通过调用glGetUniformLocation单独查询位置。该问题在this博文中有所描述。