A testbed for shader editing for shaders used by SpriteKit.
Most shaders are available as examples for ShaderToy but there are minor differences between the GLSL used there and that of SpriteKit.
Note that much of this sample has comments referring to tg classes from Touchgram. SKShaderToy is a testbed for some ideas used in that app so methods were copied across, but there's no build or runtime dependency.
