Chapter 6
Blending, Antialiasing, Fog, and Polygon Offset

Chapter Objectives

After reading this chapter, you'll be able to do the following:

• Blend colors to achieve such effects as making objects appear translucent
• Smooth jagged edges of lines and polygons with antialiasing
• Create scenes with realistic atmospheric effects
• Draw geometry at or near the same depth, but avoid unaesthetic artifacts from intersecting geometry

The preceding chapters have given you the basic information you need to create a computer-graphics scene; you've learned how to do the following:

• Draw geometric shapes
• Transform those geometric shapes so that they can be viewed from whatever perspective you wish
• Specify how the geometric shapes in your scene should be colored and shaded
• Add lights and indicate how they should affect the shapes in your scene

Now you're ready to get a little fancier. This chapter discusses four techniques that can add extra detail and polish to your scene. None of these techniques is hard to use - in fact, it's probably harder to explain them than to use them. Each of these techniques is described in its own major section:

• "Blending" tells you how to specify a blending function that combines color values from a source and a destination. The final effect is that parts of your scene appear translucent.
• "Antialiasing" explains this relatively subtle technique that alters colors so that the edges of points, lines, and polygons appear smooth rather than angular and jagged.
• "Fog" describes how to create the illusion of depth by computing the color values of an object based on its distance from the viewpoint. Thus, objects that are far away appear to fade into the background, just as they do in real life.
• If you've tried to draw a wireframe outline atop a shaded object and used the same vertices, you've probably noticed some ugly visual artifacts. "Polygon Offset" shows you how to tweak (offset) depth values to make an outlined, shaded object look beautiful