What is gl_ModelViewMatrix and gl_ModelViewProjectionMatrix in modern OpenGL?

Question

I have this code which is context "#version 330 core"

gl_Position =           PerspectiveViewMatrix(90.0, AspectRatio, 0.01, 1000.0  )


                        *    TranslationMatrix(0, 0, -4 -0.35*MouseWheel)        


                        *    RotationMatrix(MouseMovement.y, X_AXIS)        
                        *    RotationMatrix(-MouseMovement.x, Y_AXIS)    
                        *    RotationMatrix(float(Strafing*3), Z_AXIS)    


                        *    TransformationMatrix

                        *    in_Vertex;

Which part of it is old gl_ModelViewMatrix and which part is gl_ModelViewProjectionMatrix? (What is gl_ProjectionMatrix that was used to create ModelViewProjection?)

Answer 1

I'm not too familiar with GLSL 3.3, but I bet that PerspectiveViewMatrix (is it even builin functionality?) constructs matrix that replaces old builtin gl_ProjectionMatrix

gl_ModelViewMatrix in general is the product of object's transformation matrix in world space and its own "local" transformation, so it can be defined as the product of TranslationMatrix, RotationMatrix and TransformationMatrix.

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You need to send all the matrices to the shader yourself, e.g. as uniforms. These matrices you need to build yourself (e.g. using GLM). Lazy example for a projection matrix:

// in your app

std::array<GLfloat, 16> projection;

glMatrixMode(GL_PROJECTION);
glPushMatrix();
gluOrtho(...);
glGetFloatv(GL_PROJECTION_MATRIX, projection.data());
glPopMatrix();

glUniformMatrix4fv(glGetUniformLocation(ShaderProgramID, "ProjectionMatrix"), 1, GL_FALSE, projection.data());

// in vertex shader

uniform mat4 ProjectionMatrix;
in vec4 InVertex;

void main() {
    gl_Position = ProjectionMatrix * InVertex;
}