2020-09-21 Wenson Hsieh <wenson_hsieh@apple.com>

[GPU Process] Several tests in canvas/philip/tests are failing with text diffs

https://bugs.webkit.org/show_bug.cgi?id=216800

Reviewed by Darin Adler.

When using the GPU process to render canvas elements, we currently fail the 7 tests in `canvas/philip/tests`

below, due to gradient and pattern fill/stroke styles lingering on the 2D graphics context state after a fill or

stroke color is set, respectively.

This happens when:

1. The fill color is set to a color `C`.

2. A fill pattern or gradient is applied.

3. The fill color is set to the color `C` again.

In this case, after step (2), we propagate a graphics context state change indicating that the fill pattern has

changed, but we leave the fill color unchanged (i.e., it remains equal to `C`). In step (3), we then set the

fill color to `C` again, which doesn't propagate a state change to the GPU process, since the fill color is the

same (`C`). As such, the state in the GPU process keeps its fill gradient, and we end up filling with this old

gradient instead of the fill color `C`.

To fix this, we simply revert `fillColor` and `strokeColor` to the invalid color when setting a gradient or

pattern in the same way that we currently clear out the fill/stroke gradient and pattern when setting a fill/

stroke color, which ensures that a state change will be sent to the GPU process during step (3).

Fixes the following canvas-related layout tests when using the GPU process:

- canvas/philip/tests/2d.gradient.radial.cone.shape2.html

- canvas/philip/tests/2d.pattern.basic.nocontext.html

- canvas/philip/tests/2d.pattern.paint.norepeat.coord3.html

- canvas/philip/tests/2d.pattern.paint.repeatx.coord1.html

- canvas/philip/tests/2d.pattern.paint.repeatx.outside.html

- canvas/philip/tests/2d.pattern.paint.repeaty.coord1.html

- canvas/philip/tests/2d.pattern.paint.repeaty.outside.html

The entire canvas/ directory is currently skipped when enabling the GPU process for canvas rendering, but once

we're down to a smaller number of failures, I intend to unskip these directories for GPU process, and

individually track any remaining test failures.

* platform/graphics/GraphicsContext.cpp:

(WebCore::GraphicsContext::setStrokePattern):

(WebCore::GraphicsContext::setFillPattern):

(WebCore::GraphicsContext::setStrokeGradient):

(WebCore::GraphicsContext::setFillGradient):