Sweep gradient can only easily be implemented in Skia

[justvanrossum]

Skia has GradientShader.MakeSweep but the other libraries and SVG don't have native support for it, as far as I know.

[justvanrossum]

(FWIW, PaintSweepGradient has now been implemented in the Skia backend.)

[horasio]

For the other backend/canvases, we can probably do an approximation with a triangle fan (say ≈360 triangles), with a constant color in each triangle. Generate triangle -> clip/cull against clip-extent -> draw.
Would that be useful?
Could also be a linear gradient in each triangle, but i'm not sure it would look good. Worth a try anyway.

[horasio]

In fact, mesh patterns seems the way to go, in order to get better approx.
Let me experiment...

[justvanrossum]

Ah great, I see Cairo supports mesh patterns, so that may be a good solution there.

For SVG, a triangle approximation is probably best. SVG to me is more a reference, so I wouldn't be bothered much about effiency.

I wonder if for CoreGraphics, CGShading could be an option (although I can imagine that being performant in Python, if that API is supported at all by the Python bridge). I have never used that API.

In the worst case we just don't support sweep gradients in some backends.

[horasio]

Should that issue be closed?

[justvanrossum]

Yes, let's continue in #17.