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<html><head><link rel="stylesheet" href="style.css"></head><body><div class="page">
<h1>20161023 - Sphere Tracing AA</h1>
<br>
<i>General idea for anti-aliasing with sphere tracing. The end result of this would be a very analog film feeling image with grain...</i>
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<br>
<strong>Ray Directions</strong> - Shoot one ray per pixel and use a good temporally changing low discrepancy sampling for ray direction.
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<strong>First Hit</strong> - Trace forward until 2D projected distance to surface is within pixel diameter.
I'm using diameter here because one wants a thin feature to show up as partial coverage across at least 2 pixels (to get good AA).
Likely this distance needs a tuning knob, best might be half between pixel radius and diameter, depends on visual preference.
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<strong>Coverage</strong> - Compute pixel coverage and store coverage with ray output.
This part I'm speculating on and would need to try to see what works.
Initial idea: step one more time through the surface,
then take the last 2 distance samplings and try to estimate the actual surface,
sample the distance function at the estimated surface,
take this final distance as "coverage"
(on surface = full coverage, reduce coverage as distance increases).
Exact coverage isn't as important has having coverage approach zero as ray passes a surface without getting near enough.
Error on surfaces will just show up as temporal grain, which is visually pleasing.
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<strong>Reconstruction</strong> - For each pixel take nearest 11 rays.
Take a weighted sum of ray colors where weight is <tt>F(DistanceFromRayToPixelCenter) * Coverage</tt> then divide by sum of weight.
The <tt>F()</tt> function is the filter kernel, where fastest (but not highest quality) is the Gaussian,
<tt>exp2(-scale*dst*dst)</tt>.
Could also do disk average (return 1.0 under a given radius, and some smooth fall-off outside that radius).
Note <tt>DistanceFromRayToPixelCenter</tt> is constantly changing temporally due to low discrepancy sampling.
Also nearest 11 rays is a fixed pattern,
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<pre>
XXX
XXOXX <-- 11 sample pattern
XXX</pre>
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<strong>Grain</strong> - After reconstruction add some grain to help mask the temporally changing sampling pattern.
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