This change improves performance of the AgX tonemapper by allowing two matrix multiplications to be combined into one. This comes at the cost of loss of color information that could be correctly interpreted as positive RGB values in the Rec. 2020 color space. Additionally, an insignificant amount of error is intentionally introduced to the input color value to prevent the need for a second max function call before log2. The final negative color clipping has been removed to allow the tonemapper to return negative RGB values, similar to other tonemappers in Godot.
This changes the polynomial function so that a lower input always results in a lower output and vice-versa. Additionally, the new function returns a value that is much closer to 1.0 when given an input of 1.0.
Technical implementation notes:
- Moved linearization step to before the outset matrix is applied and
changed polynomial contrast curve approximation.
- This does *not* implement Blender's chroma rotation to address hue shift.
This hue rotation was found to have a significant performance impact.
- Improved performance by combining the AgX outset matrix with the Rec 2020 matrix.
Co-authored-by: Allen Pestaluky <allenpestaluky@gmail.com>
Co-authored-by: Clay John <claynjohn@gmail.com>
