# Post Processing

Many effects can be achieved via mere post-processing on raw pixel data, without any geometry processing at all. Trial offers a simple interface for such effects, the post-effect-pass and simple-post-effect-pass. A post effect pass is a pass that takes a number of input textures, and outputs a number of output textures, simply running a fragment shader for every output pixel.

The simple version always declares an input port called previous-pass and an output port called color. Using the port texspec you can further customise things such as the resolution of the textures, internal format, etc. See shader passes for more info on that.

Typically you'll then just implement a fragment shader on your class, using the uv input variable, and the color output variable.

Presets

Trial also ships a number of useful preset post processing passes:

• copy-pass
  Just copies the texture.

• negative-pass
  Negates the colours. Only works on low dynamic range.

• box-blur-pass
  Applies a box blur to the image.

• sobel-pass
  Applies a sobel edge detection filter.

• gaussian-blur-pass
  Applies a gaussian blur in a single direction.

• radial-blur-pass
  Applies a radial blur with a specific origin.

• swirl-pass
  Swirl the pixel around the center of a circle.

• fxaa
  A very easy-to-use and cheap anti-aliasing pass.

• blend-pass
  Blends two images (a-pass, b-pass) together using one of many blending methods.

• high-pass-filter
  Only keeps pixels with a luminance above the threshold. Others are set to transparent.

• low-pass-filter
  Only keeps pixels with a luminance below the threshold. Others are set to transparent.

• chromatic-aberration-filter
  Applies a chromatic aberration effect, shifting the three colour channels separately.

• luminance-pass
  Outputs a grayscale version based on the color luminance.

• light-scatter-pass
  Performs a light scattering effect.

• visualizer-pass
  Composes one or more textures (t[0]...t[3]) together for easier debug viewing.