OpenGL 纹理单元 纹理目标 理解 glActiveTexture glBindTexture

转载自：
http://blog.csdn.net/zhuyingqingfen/article/details/19968341

可以这样简单的理解为：显卡中有N个纹理单元（具体数目依赖你的显卡能力），每个纹理单元（GL_TEXTURE0、GL_TEXTURE1等）都有GL_TEXTURE_1D、GL_TEXTURE_2D等，如下代码：

 struct TextureUnit
 {
     GLuint targetTexture1D;
     GLuint targetTexture2D;
     GLuint targetTexture3D;
     GLuint targetTextureCube;
     ...
 };

 TextureUnit textureUnits[GL_MAX_TEXTURE_IMAGE_UNITS]
 GLuint currentTextureUnit = 0;

默认情况下当前活跃的纹理单元为0.

 

 void glActiveTexture(GLenum textureUnit)
 {
     currentTextureUnit = textureUnit  - GL_TEXTURE0 ;
 }

glActiveTextue 并不是激活纹理单元，而是选择当前活跃的纹理单元。

 void glBindTexture(GLenum textureTarget, GLuint textureObject)
 {
     TextureUnit *texUnit = &textureUnits[currentTextureUnit];
     switch(textureTarget)
     {
     case GL_TEXTURE_1D: texUnit->targetTexture1D = textureObject; break;
     case GL_TEXTURE_2D: texUnit->targetTexture2D = textureObject; break;
     case GL_TEXTURE_3D: texUnit->targetTexture3D = textureObject; break;
     case GL_TEXTURE_CUBEMAP: texUnit->targetTextureCube = textureObject; break;
     }
 }

从示例代码中可以看到：当绑定纹理目标时，所作用的是当前活跃的纹理单元。

可以这样简单的理解为：显卡中有N个纹理单元（具体数目依赖你的显卡能力），每个纹理单元（GL_TEXTURE0、GL_TEXTURE1等）都有GL_TEXTURE_1D、GL_TEXTURE_2D等，如下代码：

 struct TextureUnit
 {
     GLuint targetTexture1D;
     GLuint targetTexture2D;
     GLuint targetTexture3D;
     GLuint targetTextureCube;
     ...
 };

 TextureUnit textureUnits[GL_MAX_TEXTURE_IMAGE_UNITS]
 GLuint currentTextureUnit = 0;

默认情况下当前活跃的纹理单元为0.

 

 void glActiveTexture(GLenum textureUnit)
 {
     currentTextureUnit = textureUnit  - GL_TEXTURE0 ;
 }

glActiveTextue 并不是激活纹理单元，而是选择当前活跃的纹理单元。

 void glBindTexture(GLenum textureTarget, GLuint textureObject)
 {
     TextureUnit *texUnit = &textureUnits[currentTextureUnit];
     switch(textureTarget)
     {
     case GL_TEXTURE_1D: texUnit->targetTexture1D = textureObject; break;
     case GL_TEXTURE_2D: texUnit->targetTexture2D = textureObject; break;
     case GL_TEXTURE_3D: texUnit->targetTexture3D = textureObject; break;
     case GL_TEXTURE_CUBEMAP: texUnit->targetTextureCube = textureObject; break;
     }
 }

从示例代码中可以看到：当绑定纹理目标时，所作用的是当前活跃的纹理单元。