Solves #700

[hozuki]

Replaced perspective view matrix calculation when given FOV and aspect
ratio. The new implementation does not calculate the view rectangle, so
the result matrix is still valid when znear = 0.

[xoofx]

Thanks, it is merged.

[hozuki]

Although this commit ensures that the result matrix is made up of "ordinary" floating point numbers, the matrix itself is still invalid to be a projection matrix. Setting znear to 0 makes all elements in the 4th row become 0, and the projection transform will fail, resulting in unexpected Z orders if you make multiple draw calls.

[xoofx]

I'm not sure what do you expect from using a znear 0, as the result projection matrix column ending with zeros is perfectly normal and valid, that's the formula. It is a degenerated case, but nobody expect to set znear = 0, so it doesn't make sense at all. Not sure why you seem to be so annoyed by this. It is like complaining that dividing a number by 0 is not valid.

If you want to use infinite projection matrix, you can use a different formula as described in Tightening the Precision of Perspective Rendering, and as you can note, that's only the far plane that is discarded, not the near plane that need to be here in order to perform proper "clipping/clamping" of the zvalue when z approach the near plane.