Physically Based Rendering

[Robadob]

Setup a branch PBR, from the EnvironmentMaps branch. Hoping to replace the material/lighting support so that we can use PBR exclusively.

The work is based on the LearnOpenGL.com guide's, with a bunch of changes.

This update will also introduce Bloom, HDR and Gamma correction as these are all rather trivial additions to implement (albeit only if we make them enabled by default) throughout.

[Robadob]

I have:

• Setup Bloom filter
• Updated Materials and Lights to match PBR format
• Added decent sample PBR model (this).

I need to:

• Handle SRGB textures
• Include the PBR test shader
• Re-add MSAA support
• Add skybox Equirectangular to Cubemap conversion
• Add auto exposure tonemapping
  • Build 16 bucket histogram
    • linear space luminance values between 0.5 and 4.00, wider buckets at the higher range
    • Update one bucket per frame, via an asynchronous occlusion query, render quad equal to screen space, discard fragements not inside bucket.
    • ? Target upper bound so that 5% of bright pixels not exposed
    • ? Limit lower bound so median is always in range?
    • Make the 5% mark slow to change, to prevent blinking with flashing lights.
    • Might be faster to calculate using compute shader reduction (mock code here).
    • Ideally Draw shader should sit outside tonemapping.

[Robadob]

Main stalling point here was the requirement of HDR lightmaps to do proper PBR.