Improve reflection probes seams

[vorg]

Currently pex-renderer uses Octahedral maps for reflection probes as explained in Octahedral maps for PREM #8.

There is number of never addressed issues though:

• the resolution of the reflection probe is not configurable and hardcoded at 2048 (1024 for "roughness 0" reflection)
• a seem might be visible on the higher roughness levels
• there are visible birth spots on high contrast HDRIs with single bright spot

[vorg]

About seams:

Engine Work: Global Illumination with Irradiance Probes

https://twitter.com/RealtimeVFXMike/status/1221525778359144450

https://twitter.com/Dan87626237/status/1220048547103563777

https://twitter.com/val_sagrario/status/1231771907437010949?s=20

float2 Encode( float3 n )
{
n /=  dot(1, abs(n));
float2 wrap = ( 1.0 - abs( n.zx ) ) * ( n.xz >= 0.0 ? 1.0 : -1.0 );
n.xy = n.y >= 0.0 ? n.xz : wrap;
n.xy = n.xy * 0.5 + 0.5;
return n.xy;
}

Scaling Probe-Based Real-Time Dynamic Global Illumination for Production

[vorg]

@dmnsgn here is what i mean by bright spots / fireflies. This might be from bugs in importance sampling or not enough blur. I think in current pex-renderer version i blur the original octahedral map into mipmap levels and sample from them but it's simple downsampling and not soft gaussian blur (not sure if that would be accurate). I do know ThreeJS blurs the reflection levels more.

[vorg]

More recent "scratches" example of insufficient filtering.