Perspective matrix for Vulkan

[fcrisafulli-dev]

I'm using nalgebra-glm to do some work with the Vulkan API through Vulkano. The perspective matrix generated by perspective_rh_zo flips the Z axis in the wrong direction. I chose this function since Vulkan operates with a right handed coordinate system and the Z axis goes from 0 to 1 rather than -1 to 1.

According to these two posts:
Why projection matrices typically used with OpenGL fail with Vulkan
Setting Up a Proper Projection Matrix for Vulkan

Following the math from the second post shows all that needs to change to create a 'proper' Vulkan perspective matrix is change:

//matrix_clip_space.rs
//pub fn perspective_rh_zo
mat[(0, 0)] = one / (aspect * tan_half_fovy);

to

mat[(0, 0)] = aspect / tan_half_fovy;

I'm not sure if a new function should be added or if the existing one should be changed.

[sebcrozet]

Hi! The existing function is supposed to follow the perspectiveRH_ZO implementation from the C++ glm library. So we can’t change its behavior to avoid confusions.

The function you are suggesting would have to be added as a new one.