13.1.3 The Framebuffer and Per-Fragment Operations

Per-fragment and framebuffer operations can be used to operate on pixels of an image in parallel. Additionally, multiple images may be combined in a variety of ways. Blending and the accumulation buffer are two areas of interest. These features are discussed in detail in Section 8. The accumulation buffer is particularly important since it provides several fundamental operations:

• Scaling of an image by a constant:
  • glAccumGL_ MULT, <scale>(GL_ MULT, <scale>)
  • glAccumGL_ LOAD, <scale>(GL_ LOAD, <scale>)
  • glAccumGL_ RETURN, <scale>(GL_ RETURN, <scale>)
• Biasing of an image by a constant:
  • glAccumGL_ ADD, <scale>(GL_ ADD, <scale>)
  • Clear of framebuffer with color <scale>, followed by glAccumGL_ LOAD, 1(GL_ LOAD, 1)
• Linear combination of two images on a pixel-by-pixel basis: glAccumGL_ LOAD, <scale1>(GL_ LOAD, <scale1>) followed by glAccumGL_ ACCUM, <scale2>(GL_ ACCUM, <scale2>)

The accumulation buffer and blending are discussed in subsequent sections in terms of the image processing operations that use them.