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A depth buffer is something that you find common nowadays, especially with the GPUs providing it essentially for free, but again it is not what makes 3D graphic

by Crinus 7y ago

A depth buffer is something that you find common nowadays, especially with the GPUs providing it essentially for free, but again it is not what makes 3D graphics and a lot of otherwise full 3D polygonal games were made without it nor it is necessary to create 3D graphics. With other approaches to 3D rendering you do not even need a depth buffer to get correct results for penetrating objects (e.g. classic raytracing). What is happening here is called "painter's algorithm" and was a very common approach for realtime graphics before depth buffers became hardware accelerated. Actually it is still often used even today for transparencies since those often cannot be rendered in arbitrary order and you need to depth sort them. One common approach to solve these issues - both then and now - is to subdivide/preprocess geometry so that wrong overlaps are not or rarely happening.

gnode 7y ago
Indeed. I avoided the term depth buffer for this reason. A depth test is still necessary on a per-pixel basis for a correct solution to the visibility problem in the general case - even if that's done by raytracing or some other method. The painters algorithm is not a general solution because it cannot handle cyclical occlusion: https://en.wikipedia.org/wiki/Painter's_algorithm#/media/File:Painters_problem.svg https://en.wikipedia.org/wiki/Painter's_algorithm#/media/Fil... Its limitations constrain the geometry which may be correctly rendered.
- Crinus 7y ago
  My point above is that to call something 3D graphics does not depend on having per-pixel correct visibility and painter's algorithm (and others) is a valid method to render 3D graphics and was for many years. Applications using it either accepted the limitation (many games did that) or tried to overcome it by preprocessing the geometry to create clusters that are unlikely to overlap or by performing subdivision on the projected polygons.

by Crinus 7y ago

gnode 7y ago

Indeed. I avoided the term depth buffer for this reason. A depth test is still necessary on a per-pixel basis for a correct solution to the visibility problem in the general case - even if that's done by raytracing or some other method. The painters algorithm is not a general solution because it cannot handle cyclical occlusion: https://en.wikipedia.org/wiki/Painter's_algorithm#/media/File:Painters_problem.svg https://en.wikipedia.org/wiki/Painter's_algorithm#/media/Fil... Its limitations constrain the geometry which may be correctly rendered.

Crinus 7y ago
My point above is that to call something 3D graphics does not depend on having per-pixel correct visibility and painter's algorithm (and others) is a valid method to render 3D graphics and was for many years. Applications using it either accepted the limitation (many games did that) or tried to overcome it by preprocessing the geometry to create clusters that are unlikely to overlap or by performing subdivision on the projected polygons.