Particle vertex

[samsartor]

A new vertex type should be added with the following parameters:

• pub pos: [f32; 3]
• pub tan: [f32; 3]
• pub bitan: [f32; 3]
• pub tex: [f32; 2]
• pub tex_size: [f32; 2]

The motivating use case for this type is the generation of quads via the geometry shader. The quad will be created like so:

• norm = tan x bitan
• pos = [pos, pos + tan, pos + tan + bitan, pos + bitan]
• tex = [tex, tex + vec2(tex.size.x, 0), tex + tex_size, tex + vec2(0, tex.size.y)]