I am trying to find if the point clicked on the screen using the mouse, fall on the mesh body rendered using directx8(and vb). The points of the mesh nodes are in 3d which i have rendered using directx's draw primitives. The picked point is the 2d mouse point. I will have to convert the 3d(node's coordinates) points into the screen coordinates and check if the picked point falls on the mesh. My understanding is that i will have to get the projection matrix and multiply it with the 3d point i am interested to get its corresponding 2d screen coordinate. Is this correct? How to get the projection matrix and multiply(projection matrix is 4X4 and 3dpoint is 3X1)Can somebody suggest how to do this?