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Z-buffering 251
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This shows that the values of are grouped much more densely near the plane, and much more sparsely
farther away, resulting in better precision closer to the camera. The smaller the ratio is, the less precision
there is far away—having the plane set too closely is a common cause of undesirable rendering artifacts in
more distant objects. [2]
To implement a z-buffer, the values of are linearly interpolated across screen space between the vertices of the
current polygon, and these intermediate values are generally stored in the z-buffer in fixed point format.
W-buffer
To implement a w-buffer, the old values of in camera space, or , are stored in the buffer, generally in floating
point format. However, these values cannot be linearly interpolated across screen space from the vertices—they
usually have to be inverted, interpolated, and then inverted again. The resulting values of , as opposed to , are
spaced evenly between and . There are implementations of the w-buffer that avoid the inversions
altogether.
Whether a z-buffer or w-buffer results in a better image depends on the application.
References
[1] The OpenGL Organization. "Open GL / FAQ 12 - The Depth buffer" (http:/ / www. opengl. org/ resources/ faq/ technical/ depthbuffer. htm). .
Retrieved 2010-11-01.
[2] Grégory Massal. "Depth buffer - the gritty details" (http:/ / www. codermind. com/ articles/ Depth-buffer-tutorial. html). . Retrieved
2008-08-03.
External links
• Learning to Love your Z-buffer (http:/ / www. sjbaker. org/ steve/ omniv/ love_your_z_buffer. html)
• Alpha-blending and the Z-buffer (http:/ / www. sjbaker. org/ steve/ omniv/ alpha_sorting. html)
Notes
Note 1: see W.K. Giloi, J.L. Encarnação, W. Straßer. "The Giloi’s School of Computer Graphics". Computer
Graphics 35 4:12–16.