osg学习（五十五）osg_ModelViewMatrix osg_ModelViewProjectionMatrix osg_ProjectionMatrix osg_NormalMatrix(代码

Posted 2021-09-12 hankern

分别替换glsl中的gl_ModelViewMatrix gl_ModelViewProjectionMatrix gl_ProjectionMatrix gl_NormalMatrix，如果没有这些则插入。

为什么要如此替换？

这些gl_*变量在早期的版本中有（330中已经没有了），如果glsl有这些变量可能会出现高版本无法使用的问题，osg同一采用新的变量好处在于，避免不同版本的不兼容性问题。在低版本可以用，在高版本也可以用。不足的地方时，需要在程序中随时更新osg_*变量。

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 ");
    }

    if (_useVertexAttributeAliasing)
    {
        State_Utils::replaceAndInsertDeclaration(source, declPos, _vertexAlias._glName,         _vertexAlias._osgName,         attributeQualifier, _vertexAlias._declaration);
        State_Utils::replaceAndInsertDeclaration(source, declPos, _normalAlias._glName,         _normalAlias._osgName,         attributeQualifier, _normalAlias._declaration);
        State_Utils::replaceAndInsertDeclaration(source, declPos, _colorAlias._glName,          _colorAlias._osgName,          attributeQualifier, _colorAlias._declaration);
        State_Utils::replaceAndInsertDeclaration(source, declPos, _secondaryColorAlias._glName, _secondaryColorAlias._osgName, attributeQualifier, _secondaryColorAlias._declaration);
        State_Utils::replaceAndInsertDeclaration(source, declPos, _fogCoordAlias._glName,       _fogCoordAlias._osgName,       attributeQualifier, _fogCoordAlias._declaration);
        for (size_t i=0; i<_texCoordAliasList.size(); i++)
        {
            const VertexAttribAlias& texCoordAlias = _texCoordAliasList[i];
            State_Utils::replaceAndInsertDeclaration(source, declPos, texCoordAlias._glName, texCoordAlias._osgName, attributeQualifier, texCoordAlias._declaration);
        }
    }
}

 更新osg_*变量