* replace one_minus_focal_x and abs_one_minus_focal_x variables with the actual expressions
* replace division by r^2-1 with multiplication by reciprocal
* revert chain selects to branchy code for clarity. Branching is dynamically uniform so shouldn't affect performance
* add suggested comment describing gradient kind/flags constants
This exchanges the per-pixel branching with additional ALU + selects. My expectation is that this will be faster, but that may be hardware/driver dependent and likely requires profiling and examination of generated code.
The original code is kept in a comment with notes to explain the more obfuscated select version.
Adds full support for COLRv1 radial gradients based on the two-point conical gradient algorithm at https://skia.org/docs/dev/design/conical/
Also adds robustness to degenerate cases in gradient encoding:
* Radial where p0 == p1 && r0 == r1 renders transparent solid
* Empty stops render as transparent solid
* Single stop renders as solid
This patch implements the pad, repeat and reflect extend modes for gradient brushes. Adds a new example demonstrating the functionality.
Also fixes a few bugs:
* Clamps alpha in blend.wgsl for the `blend_compose` function. The `Plus` mode was generating `alpha > 1.0` leading to incorrect rendering.
* Small change to radial gradients in fine.wgsl to reject pixels outside the cone when the circles don't nest. This requires further work to properly extend the cone when one of the radii is not 0.
This fixes an incorrect application of the inverse transform for radial gradients in fine.
Also fixes an edge case in `SceneBuilder` where a brush transform is identical to the path transform leading to a corrupt encoding.
The area bug was found and fixed by @dfrg, and is adapted from #239. I wanted to move it to a separate PR so that one would be more focused on API.
The other bug is currently silent because the two quantities swapped are both 4, but it is triggered when experimenting with tuning for performance.
* Move the vello crate to the root of the crate
* Add warning that README is work in progress
* Add newline in warning
* Move the unlicense into the shader folder
* Fixup wgsl-analyzer include paths
