Skia does not have built-in support for gradient transition hints. So
instead of adding custom gradient painting, now we do the same thing as
other engines and preprocess color stops by replacing transition hints
with a bunch of points lying between adjacent color stops and calculated
using non-linear formula from the spec. As a result we get visually
close enough rendering we would get by applying spec-formula
individually to each point of a gradient.
This moves the CSS gradient painting to the painter creating:
- Painter::fill_rect_with_linear_gradient()
- Painter::fill_rect_with_conic_gradient()
- Painter::fill_rect_with_radial_gradient()
This has a few benefits:
- The gradients can now easily respect the painter scale
- The Painter::fill_pixels() escape hatch can be removed
- We can remove the old fixed color stop gradient code
- The old functions are now just a shim
- Anywhere can now easily use this gradient painting code!
This only leaves the color stop resolution in LibWeb (which is fine).
Just means in LibGfx you have to actually specify color stop positions.
(Also while here add a small optimization to avoid generating
excessively long gradient lines)