Toy toy toy!!!

TODO:
Build particle system.
Steps:

• Spawn and recycle particles. Texture. CPU? Compute Shader?
• Update speed and positions. Physics. Texture. In one Pass? CPU? Compute Shader?
• Sort by depth. Maybe?
• Render. Instancing (draw from back to front if sorted). Geometry shader.

First try (Top to down. Static particles. Simple move.):

• Initialize some particles at top of screen.
• Update position with constant speed.
• Render with instancing and geometry shader.