PCC / VCT hybrid progress

by Matias Goldberg | Aug 14, 2019 | News

Last time I mentioned we were working on PCC / VCT Hybrid (PCC = Parallax Corrected Cubemaps, VCT = Voxel Cone Tracing).

I just implemented storing depth into the alpha channel, which is used to improve the quality of the hybrid.

Because we often use RGBA8 cubemaps, 8-bits is not enough to store the depth. Therefore we only store the deviation from the ideal probe shape.

The original PCC algorithm boils down to:

    posInProbeShape = cameraCenter + reflDir * fDistance;

Where cameraCenter is artist-defined (where the PCC camera was placed to build the probe) and posInProbeShape is also artist-defined (by controlling the size of the probe)

PCC is about finding reflDir mathematically:

    reflDir = (posInProbeShape - cameraCenter) / fDistance;

However we already know reflDir after executing PCC’s code.

Now the depth compression comes to effect by slightly altering the formula:

    realReconstructedPosition = cameraCenter + reflDir * fDistance * depthDeviation;

The variable depthDeviation is in range [0; 2] (which we store in the alpha channel) and thus 8-bit should be enough.

Technically this could introduce a few artifacts because we only store the depth in range [0; maximum_distance * 2]

Storing the depth deviation dramatically improves the hybrid’s quality!

But let’s not rush.