Thorsten Froehlich wrote:

> In article <3ee4e321$1@news.povray.org> , sascha
> <sas### [at] userssourceforgenet>  wrote:
> 
> No, the problem is, you cannot optimise the scanline algorithm further
> than
> what I outlined (at least not bringing down the complexity).  In fact, the
> complexity I outlined holds for the first implementations 30 or so years
> ago
> and it still holds in the 3d hardware accelerators of today.  The main
> benefit of the scanline algorithm is that you can make the constant time
> factor very, very small compared to ray-tracing.
> 
>> But couldn't the same (or other - e.g. octree) optimizations be applied
>> to the scanline algorithm too?
> 
> No, because the scanline algorithm requires you to draw everything in the
> viewing area to determine its visibility.  You can cull backfacing
> triangles, but that only divides to constant factor by about two.

Well, there is further optimisation possible: view-frustum culling and
occlusion culling. You can determine on the CPU (using some Bounding Volume
Hierarchies) which groups of triangles are not visible from the viewpoint.
For example a scene in a house you can quickly determine which rooms one
sees into at all and which you don't. So there is no need to move these
triangles down the rendering pipline. Of course this triangle exculsion is
only an conservative estimation and no exact solution.

Another interesting thing to think about is: Why do we use triangles? As
today there are often tens of triangles per pixel in a detailed model one
doesn't really need the full triangles. So another idea is to stick to
points and not store the interconnections of the points but only the points
assosiated with a normal and a texture. This reduces the memory
requirements. For the rendering you draw either a small box for each point
(which is supported by todays GPUs) or more exact a small ellipse. Using
points as basing privmitives has another advantage: You can quickly
generate different LODs of models (which is much slower for triangle
meshs), so you can use a reduced-point version when an object is farther
away.

That this actuallly works can be seen in the video from:
http://www9.informatik.uni-erlangen.de/Research/Rendering/SPT

- Micha

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POV-Ray Objects Collection: http://objects.povworld.org

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