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OpenGL gradient rendering improvements and additions

Fabio Lagalla requested to merge fl/gtk:wip/fl/gl-gradients into master

This patch improves performance on MacOS by:

  • Evaluating gradient data which is intended to be constant per-draw call and pass it as shader uniforms
  • Reducing alu operations by:
    • Exploiting algebric and geometric identities (example: projection of point to segment)
    • Avoiding integer to float conversions in favor of interpolated coords in the object frame
    • Avoiding shader divisions by uniforms and constants, whenever possible
    • Perform color premultiplication on the host then passing already premultiplied colors

System information

  • MacOS Catalina 10.15.7
  • CPU: 2.8 GHz Intel Core i7 quad-core
  • Memory: 16 GB 2133 MHz LPDDR3
  • GPU: Intel Iris Plus Graphics 655 1536 MB
  • Benchmark: fishbowl (from gtk4-demo)
  • Widget type: button
  • Count: 512

Results

vsync on:

Master This merge request
15 fps 30 fps

vsync off:

Master This merge request
14 fps 41 fps

No other improvements / regressions detected on the other widget types.

Second part of the patch adds support for repeating gradients, by adding a new uniform repeat that performs wrapping in [0, 1] when set to true. This allows to avoid rendering a fallback node.

Edited by Fabio Lagalla

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