GLSL ES1.0 并将纹理单元索引传递给片段着色器？

Question

正在尝试将 vertex/frag 着色器从 glsl 330 转换为 glsl es1.0
（基本上退后一步，因为原始应用程序是为桌面版本的 OpenGL3.0 编写的，但 webGL2.0 仍然没有得到某些浏览器的完全支持，如 IE 或 Safari；据我所知）。

我知道 1.0 使用的是 attribute/varying 而不是 in/out，但我遇到了一个问题不能使用带有变化的整数。有一个每顶点整数值数组，表示该顶点的纹理单元索引。我看不到将该信息传达给片段着色器的方法。如果我将值作为浮点数发送，它将开始插值。对吗？

#version 330 //for openGL 3.3
//VERTEX shader
//---------------------------------------------------------------------------------
//uniform variables stay constant for the whole glDraw call
uniform mat4   ProjViewModelMatrix; 
uniform mat4   NormalsMatrix;       
uniform vec4   DefaultColor;        
uniform vec4   LightColor;          
uniform vec3   LightPosition;       
uniform float  LightIntensity;      
uniform bool   ExcludeFromLight;    
//---------------------------------------------------------------------------------
//non-uniform variables get fed per vertex from the buffers
layout (location=0) in vec3 VertexCoord;  
layout (location=1) in vec4 VertexColor;  
layout (location=2) in vec3 VertexNormal; 
layout (location=3) in vec2 VertexUVcoord;
layout (location=4) in int  vertexTexUnit;
//---------------------------------------------------------------------------------
//Output variables to fragment shader
     out vec4  thisColor;          
     out vec2  vertexUVcoord;
flat out int   TexUnitIdx;         // <------ PROBLEM
     out float VertLightIntensity; 
//---------------------------------------------------------------------------------

void main ()
{ /* ... blah ... */ }

需要翻译的伴随片段着色器如下所示

#version 330 //for openGL 3.3
//FRAGMENT shader
//---------------------------------------------------------------------------------
//uniform variables
uniform bool      useTextures;     //If no textures, don't bother reading the TextureUnit array
uniform vec4      AmbientColor;    //Background illumination
uniform sampler2D TextureUnit[6];  //Allow up to 6 texture units per draw call
//---------------------------------------------------------------------------------
//non-uniform variables
     in  vec2  vertexUVcoord;      
     in  vec4  thisColor;          
flat in  int   TexUnitIdx;         // <------ PROBLEM
     in  float VertLightIntensity;
//---------------------------------------------------------------------------------
//Output color to graphics card
out vec4 pixelColor;
//---------------------------------------------------------------------------------

void main ()
{ /* ... blah ... */ }

Answer 1

GLSL ES 1.0 中没有基于整数的属性

您当然可以传入浮点数（并以无符号字节形式提供）。调用 gl.vertexAttribPointer

时传入 false 作为规范化标志

另一方面，GLSL ES 1.0 和 GLSL ES 3.00 都不允许索引采样器数组。

来自spec

12.30 Dynamic Indexing

...

Indexing of arrays of samplers by constant-index-expressions is supported in GLSL ES 1.00. A constant-index-expression is an expression formed from constant-expressions and certain loop indices, defined for a subset of loop constructs. Should this functionality be included in GLSL ES 3.00?

RESOLUTION: No. Arrays of samplers may only be indexed by constant-integral-expressions.

"Should this functionality be included in GLSL ES 3.00?" 意味着 GLES ES 3.00

中应该包含采样器的 动态索引

我引用了 GLSL ES 3.00 规范，因为它也引用了 GLSL ES 1.0 规范。

因此，您必须编写代码，使您的独立代码成为常量索引表达式。

attribute float TexUnitNdx;  

...

uniform sampler2D TextureUnit[6];

vec4 getValueFromSamplerArray(float ndx, vec2 uv) {
  if (ndx < .5) {
   return texture2D(TextureUnit[0], uv);
  } else if (ndx < 1.5) {
   return texture2D(TextureUnit[1], uv);
  } else if (ndx < 2.5) {
   return texture2D(TextureUnit[2], uv);
  } else if (ndx < 3.5) {
   return texture2D(TextureUnit[3], uv);
  } else if (ndx < 4.5) {
   return texture2D(TextureUnit[4], uv);
  } else {
   return texture2D(TextureUnit[5], uv);
  }
}

vec4 color = getValueFromSamplerArray(TexUnitNdx, someTexCoord);

或类似的东西。将你的 ifs 安排成二进制搜索可能会更快。

GLSL ES1.0 并将纹理单元索引传递给片段着色器？

GLSL ES1.0 and passing texture-unit indices to the fragment shader?

glsl

webgl

12.30 Dynamic Indexing