The Frame Buffer and Per-Fragment Operations

Per-fragment and frame buffer operations can be used to perform operations on pixels of an image in parallel. Additionally, multiple images may be combined in a variety of ways. Two main features are of interest: blending and the accumulation buffer. These features were discussed in detail in section 6. 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 frame buffer with color <scale>, followed by glAccumGL_LOAD, 1(GL_LOAD, 1)
• Linear combination of two images on a pixel-by-pixel basis: glAccumGL_LOAD, <bias1>(GL_LOAD, <bias1>) followed by glAccumGL_ACCUM, <bias2>(GL_ACCUM, <bias2>)

The accumulation buffer and blending will be discussed in subsequent sections in terms of the image processing operations they are used to implement.