Bokeh Particle Depth of Field

This is a shader for particles to create a bokeh-esque depth of field effect.

It works by essentially “precomputing” the various amounts of blur, instead of blurring in real time. Since the particles are radial, we can store only a single row of pixels per blur level, and the shader will distort the UV coordinates to turn it into a circle. This gives us a very compact 512×1024 texture that stores 1024 different blur levels, which can be smoothly interpolated.