Comparison With Z-buffer Algorithm
(This section is misleading, because it implies that Z-buffering and scanline rendering are mutually exclusive, which is not the case. Z-buffering is primarily a method of ensuring that occlusion between objects is calculated correctly, and is often used in conjunction with scanline rasterizers. Maybe this section should be removed, because Z-buffering isn't an algorithm to contrast with -- rather it is an augmentation to scanline rasterization.)
The main advantage of scanline rendering over Z-buffering is that visible pixels are only ever processed once—a benefit for the case of high resolution or expensive shading computations.
In modern Z-buffer systems, similar benefits can be gained through rough front-to-back sorting (approaching the 'reverse painters algorithm'), early Z-reject (in conjunction with hierarchical Z), and less common deferred rendering techniques possible on programmable GPUs.
Scanline techniques working on the raster have the drawback that overload is not handled gracefully.
The technique is not considered to scale well as the number of primitives increases. This is because of the size of the intermediate datastructures required during rendering—which can exceed the size of a Z-buffer for a complex scene.
Consequently, in contemporary interactive graphics applications, the Z-buffer has become ubiquitous. The Z-buffer allows larger volumes of primitives to be traversed linearly, in parallel, in a manner friendly to modern hardware. Transformed coordinates, attribute gradients, etc., need never leave the graphics chip; only the visible pixels and depth values are stored.
Read more about this topic: Scanline Rendering
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