Oblique projection in xna

Question

Im trying to achieve oblique projection ( http://en.wikipedia.org/wiki/Oblique_projection ) in the xna framework:

float cos = (float)Math.Cos(DegreeToRadian(45)) * -1; 
float sin = (float)Math.Sin(DegreeToRadian(45)) * -1; 

Matrix obliqueProjection = new Matrix( 
                                  1, 0, cos, 0, 
                                  0, 1, sin, 0, 
                                  0, 0, 1,   0, 
                                  0, 0, 0,   1); 

Matrix orthographicProjection = Matrix.CreateOrthographic(10, 10, -1, 100000); 

projection = orthographicProjection*obliqueProjection; 

As you can see im just multiplying orthographic with oblique projection.

What i get is this:

http://imageshack.us/photo/my-images/835/oblique1.png/

Its basically what orthographic projection would look like, but with some weird far clipping.

How can i achieve proper oblique projection? Thx in advance

Answer 1

Answered by Diki: http://forums.create.msdn.com/forums/p/85032/513412.aspx#513412

Code needs to be changed like this:

Matrix obliqueProjection = new Matrix(  
                                  1,   0,   0,   0,  
                                  0,   1,   0,   0,  
                                  cos, sin, 1,   0,  
                                  0,   0,   0,   1);  

projection = obliqueProjection * orthographicProjection;  

Answer 2

For starters, you can implement the proper formula.

The wikipedia article says the projection matrix uses 0.5 * cos and 0.5 * sin while your version uses just cos and sin.