A question about view project matrix calculated from camera.

Questions & Answers
1

Hello,
I’m trying to calculate viewProject matrix , and set it to my custom shader . such as:

        Matrix4x4 proj = m_camera.projectionMatrix;
        Matrix4x4 view = m_camera.worldToCameraMatrix;
        var myViewProj = proj * view;
        Shader.SetGlobalMatrix("_myViewProj", myViewProj );

My shader like this:

       o.pos = mul( _myViewProj, mul(_Object2World, v.vertex ));

and it works wrong , nothing on screen.

if modify it to mul( UNITY_MATRIX_MVP, v.vertex ) , it works well. Why???

2

MVP is Model - View - Projection, the multiplication of 3 matrices together. You only multiply 2 matrices.

The M stands for the Model of the object matrix, the V is the camera View matrix and the P is the Projection matrix.

Your vertex is an independent point. For it to be converted to a screen point, it needs to go through those three.

You get the vertex in world coordinates (3D), then in camera coordinates (3D) and finally the projection converts it to a screen coordinates (2D).

Also, MxVxP is not MxPxV nor PxVxM. Just to say that the order matters.