如何在OpenGL片段着色器中分配数组？

Question

下面是我尝试使用的代码片段(在OpenGL es2.0中，OpenGLES GLSLes1.00中)：

GLchar strFragmentShader[] =  
"precision mediump float;                                              \n"
"varying vec2 vTexCoord;                                               \n"
"uniform sampler2D sTexture;                                           \n"
"uniform float offset[] = float[]( 0.0000, 1.3846, 3.2307);            \n"
"uniform float weight[] = float[]( 0.2270, 0.3162, 0.0702);            \n"
"void main()                                                           \n"
"{                                                                     \n"
"  vec4 sum = texture2D( sTexture, vec2(vTexCoord)/1024.0)*weight[0];  \n"
"  for (int i=0;i<3;i++) {                                                                 \n"
"    sum += texture2D( sTexture, ( vec2(vTexCoord+vec2(0.0,offset[i])/1024.0 )*weight[i];  \n"
"    sum += texture2D( sTexture, ( vec2(vTexCoord-vec2(0.0,offset[i])/1024.0 )*weight[i];  \n"
"  }                                                                                       \n"  
"  gl_FragColor = sum;                                                 \n"
"}                                                                     \n";

我基本上遵循了此页上的示例，但我得到了ERROR:LEX/PARSE-1 (fragment shader, line 4) Syntax error。

如果我试图将它们声明为const，而不是按照建议的这里 (数组构造函数下)声明uniform，则会得到ERROR:CUSTOM-5 (fragment shader, line 4) Array cannot be const。

显然，第4行和第5行也会遇到同样的问题。我如何将其编译？正确的语法是什么？

Answer 1

原来这只是GLES的一个限制。那是做不到的。需要找到另一种方法。

Answer 2

我会这样做：

GLchar strFragmentShader[] =  
"precision mediump float;                                              \n"
"varying vec2 vTexCoord;                                               \n"
"uniform sampler2D sTexture;                                           \n"
"void main()                                                           \n"
"{ 
"   vec3 offset = vec3(0.0000, 1.3846, 3.2307);            \n"
"   vec3 weight = vec3( 0.2270, 0.3162, 0.0702);            \n"                                                                    \n"
"  vec4 sum = texture2D( sTexture, vec2(vTexCoord)/1024.0)*weight[0];  \n"
"  for (int i=0;i<3;i++) {                                                                 \n"
"    sum += texture2D( sTexture, ( vec2(vTexCoord+vec2(0.0,offset[i])/1024.0 )*weight[i];  \n"
"    sum += texture2D( sTexture, ( vec2(vTexCoord-vec2(0.0,offset[i])/1024.0 )*weight[i];  \n"
"  }                                                                                       \n"  
"  gl_FragColor = sum;                                                 \n"
"}" 

或者这个如果你需要它作为制服传递给着色器：

GLchar strFragmentShader[] =  
"precision mediump float;                                              \n"
"varying vec2 vTexCoord;                                               \n"
"uniform sampler2D sTexture;                                           \n"
"uniform vec3 offset;                                                    \n"
"uniform  vec3 weight;                                                  \n" 
"void main()                                                           \n"
"{                                                                    \n"
"  vec4 sum = texture2D( sTexture, vec2(vTexCoord)/1024.0)*weight[0];  \n"
"  for (int i=0;i<3;i++) {                                                                 \n"
"    sum += texture2D( sTexture, ( vec2(vTexCoord+vec2(0.0,offset[i])/1024.0 )*weight[i];  \n"
"    sum += texture2D( sTexture, ( vec2(vTexCoord-vec2(0.0,offset[i])/1024.0 )*weight[i];  \n"
"  }                                                                                       \n"  
"  gl_FragColor = sum;                                                 \n"
"}" 

或者使用uniform float[n]，在第二个示例中，n是所需的(常量)大小，如果需要数组，则使用const float[n]；如果需要数组，并且不希望从C++代码中传递值，则使用const float[n]。