We were transforming coordinates for SVG gradients in a pretty
convoluted way: an inverse, unscaled transformation matrix was set up in
order to work around some (old?) technical limitations.
Rework this so the coordinate transformation no longer needs to be
inversed. This fixes gradients with "userSpaceOnUse" for its
gradientUnits attribute, which might cause coordinates to lie outside of
the bounding box of the gradient.
Two tests have updated reference screenshots with minor pixel updates;
this is probably the result of floating point precision improvements by
not inversing the matrix.
One test (svg-text-effects) has a bigger change: the gradient stops seem
to have moved along the text. This does seem to match other browsers
slightly better, so I'm moving forward with this ref update.
This change introduces Skia painter available under a flag. It's not
yet match capabilities of Gfx::Painter and is not ready to replace it.
Motivation:
- The current CPU painter is a performance bottleneck on most websites.
Our own GPU painter implementation is very immature and has received
relatively little attention.
- There is ongoing effort on building painter that supports affine
transforms (AffineCommandExecutorCPU) but it is far from being on par
with the default CPU painter. Skia will allow us to immediately get
full transformation support for all painting commands.
GPU painting:
I experimented with Ganesh GPU-backend, however profiling revealed that
without sharing viewport texture between WebContent and Browser
processes, it won't bring much performance improvement compared to
CPU-backend. Therefore, I decided to keep this PR focused on
implementing most of painting commands and switch to GPU-backend in
future changes.
Text rendring:
Skia painter uses glyph bitmaps produced by LibGfx. Using Skia for text
rendering will require large refactoring of the font rendering
subsystem. Currently, it's impossible to construct SkFont right before
rendering because Gfx::VectorFont can't be serialized back into sequence
of bytes.
There is a problem with ugly include paths like:
`#include <core/SkBitmap.h>`.
I would prefer to have skia prefix in the path. There was an attempt to
fix that but PR was rejected https://github.com/microsoft/vcpkg/pull/32660
Regressions compared to Gfx::Painter:
- DrawText is not implemented
- PaintTextShadow is not implemented
- PaintRadialGradient and PaintLinearGradient do not support "transition
hints" and repeat length
- PaintConicGradient is not implemented
- DrawTriangleWave is not implemented
- DrawLine does not account for line style property
- DrawScaledBitmap and DrawScaledImmutableBitmap do not account for
scaling mode property
