Re: LOS and Line Rendering

> > Aren't there problems with the Moire effect when you only trace to the
> > perimeter squares?

That's when high frequencies masquerade as low frequencies? Yeah, I noticed
that I do have that problem for large circles (as I posted above).

> Considering every traced line as a set of traversed squares, raytracing
> works if the union of tested lines doesn't have holes, i.e. every
> square is hit by at least one ray.
> It should be true for "good" line drawing algorithms that don't round
> incorrectly, and probably it can be proved; but for a practical
> implementation a brute-force automated test of all possible perimeter
> sizes and positions is easier and more reliable than a proof about an
> algorithm that might be implemented inexactly.

When I took an advanced graphics class at school we wrote a filled polygon
rasterizer, and for this to work properly, adjacent polys had to be draw
next to each other with no overlap and no unfilled pixels. This required
"perfect" line drawing.

But I don't think "perfect" line drawing can save us here. It's true that in
the continuous domain one can pick any point in a circle and come up with
the formula for a line that connects that point both to the center and a
point on the perimeter. Note that this requires that the perimeter be
infinitely divisable (otherwise you will end up drawing a bicycle wheel with
spokes). So you can't descretize the perimeter. Even if you broke each
perimeter tile into 1,000 subpixels, for a large enough circle you'll see
spokes.

Is that convincing? I thought about it for a while.

--
Blog:
Shedletsky's Bits: A Random Walk Through Manifold Space
http://www.stanford.edu/~jjshed/blog


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