Introduction

In this chapter, we focus on techniques that work directly with the pixels in a framebuffer. These techniques typically involve multiple passes. An initial pass produces the pixel data and subsequent passes apply effects or further process those pixels. To implement this we make use of the ability provided in OpenGL for rendering directly to a texture or set of textures (see Chapter 4, Rendering to a texture).

The ability to render to a texture, combined with the power of the fragment shader, opens up a huge range of possibilities. We can implement image processing techniques such as brightness, contrast, saturation, and sharpness by applying an additional process in the fragment shader prior to output. We can apply convolution filters such as edge detection, smoothing (blur), or sharpening. We'll take a closer look at convolution filters in the recipe on edge detection.

A related set of techniques involves rendering additional information to textures beyond the traditional color...