osg::TexEnvCombine 与 OpenGL API 之 glTexEnv

osg::TexEnvCombine 是 glTexEnv的封装

enum CombineParam
{
REPLACE = GL_REPLACE,//纹理颜色完全取代片段颜色
MODULATE = GL_MODULATE,//片段颜色与纹理采样颜色相乘
ADD = GL_ADD, //处理方式是片段颜色加上纹理采样的颜色
ADD_SIGNED = GL_ADD_SIGNED_ARB,
INTERPOLATE = GL_INTERPOLATE_ARB,
SUBTRACT = GL_SUBTRACT_ARB,
DOT3_RGB = GL_DOT3_RGB_ARB,
DOT3_RGBA = GL_DOT3_RGBA_ARB
};
'''