Z-buffer: Bringing Order into Chaos
What is a z-buffer? In Chapter 4, we discussed the framebuffer. It stores the color for each pixel on the screen. When OpenGL ES renders a triangle to the framebuffer, it just changes the color of the pixels that make up that triangle.
The z-buffer is very similar to the framebuffer in that it also has a storage location for each pixel on the screen. Instead of storing colors, it stores depth values. The depth value of a pixel is roughly the normalized distance of the corresponding point in 3D to the near clipping plane of the view frustum.
OpenGL ES will write a depth value for each pixel of a triangle to the z-buffer by default (if a z-buffer was created alongside the framebuffer). All you have to tell OpenGL ...
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