glActiveTexture glBindTexture

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.

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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。