AGAL - position to clip space M44 op, va0,vc0

Question

M44 op, va0,vc0 - what does it mean? this is the very first line of the vertex shader. I see it many times however I do not understand the following: Vc0 - empty 3d matrix - location of the object Va0 - vertex coordinates

Why should we multiply vector on matrix?

Thank you in advance!

Answer 1

vc0 - empty 3d matrix Why empty? In this case (and in most cases) it's MVP (model-view-projection) matrix. va0 - vertex coordinates in local space (in model space). In order to make an object change it's position. orientation, scale and in order to be visible by a camera you need to apply transformations to it. That line do exactly that.

Answer 2

The vertex shader translates and rotates every vertex in the passed vertex buffer (va0) by the passed projection matrix in vc0 (vertex constant register 0).
The vertex buffer is the list of vertices in the model being rendered.
The projection matrix is the matrix3D of the model appended with the INVERSE of the camera's matrix3D and the PerspectiveMatrix3D.
The perspectiveMatrix3D can be set up like this:

projectionmatrix.perspectiveFieldOfViewRH(45.0, swfWidth / swfHeight, 1, 15000);

...where '45.0' is the field of view, 'swfWidth / swfHeight' is the proportion of width over height, '1' is the near clipping plane and '15000' the far clipping plane.
Multiplying the models' vertices by the projection matrix in the shader orients the model to the correct position in clip space. That's why the result of the calculation can immediately be sent to the output position register (op).