osg学习（六十二）osg::State中_useModelViewAndProjectionUniforms的作用

State::State():
    Referenced(true)
{
    #if !defined(OSG_GL_FIXED_FUNCTION_AVAILABLE)
        _useModelViewAndProjectionUniforms = true;
        _useVertexAttributeAliasing = true;
    #else
        _useModelViewAndProjectionUniforms = false;
        _useVertexAttributeAliasing = false;
    #endif
}

会对一些着色器变量做替换

osg/State.cpp
bool State::convertVertexShaderSourceToOsgBuiltIns(std::string& source) const
{
    if (_useModelViewAndProjectionUniforms)
    {
        // replace ftransform as it only works with built-ins
        State_Utils::replace(source, "ftransform()", "gl_ModelViewProjectionMatrix * gl_Vertex");

        // replace built in uniform
        State_Utils::replaceAndInsertDeclaration(source, declPos, "gl_ModelViewMatrix", "osg_ModelViewMatrix", "uniform ", "mat4 ");
        State_Utils::replaceAndInsertDeclaration(source, declPos, "gl_ModelViewProjectionMatrix", "osg_ModelViewProjectionMatrix", "uniform ", "mat4 ");
        State_Utils::replaceAndInsertDeclaration(source, declPos, "gl_ProjectionMatrix", "osg_ProjectionMatrix", "uniform ", "mat4 ");
        State_Utils::replaceAndInsertDeclaration(source, declPos, "gl_NormalMatrix", "osg_NormalMatrix", "uniform ", "mat3 ");
    }
}