PBR Stuff

See in each subfolder for screenshots if any

• DoF/ includes a shader which shows a separable hexagonal filtering kernel DoF effect
• GGX includes some shaders trying out GGX Smith PBR materials
• importance_sampling/ is just a test of importance sampling for raytracing.
• LTC/ contains some tests of Linearly Transformed Cosines for Polygonal Area Light Shading and an implementation
• opengl/ is me learning how to opengl