• The projection matrix is typically a scale and perspective projection.
• The projection transformation converts the viewing frustum into a cuboid shape.

• Projection matrices to perform depth-based calculations in depth buffer or fog effects.
• Computations such as these require that your projection matrix normalize w to be equivalent to world-space z.
• In short, if your projection matrix includes a (3,4) coefficient that is not 1.
• You must scale all the coefficients by the inverse of the (3,4) coefficient to make a proper matrix

Non Compliant Matrix

			
					a 0 0 0
0 b 0 0
0 0 c e
0 0 d 0

			
	

			
	
			

		
	

Compliant Matrix

			
					a/e   0    0    0
 0   b/e   0    0
 0    0   c/e   1
 0    0   d/e   0