This modification introduces a new layer to the painting process. The
stacking context traversal no longer immediately calls the
Gfx::Painter methods. Instead, it writes serialized painting commands
into newly introduced RecordingPainter. Created list of commands is
executed later to produce resulting bitmap.
Producing painting command list will make it easier to add new
optimizations:
- It's simpler to check if the painting result is not visible in the
viewport at the command level rather than during stacking context
traversal.
- Run painting in a separate thread. The painting thread can process
serialized painting commands, while the main thread can work on the
next paintable tree and safely invalidate the previous one.
- As we consider GPU-accelerated painting support, it would be easier
to back each painting command rather than constructing an alternative
for the entire Gfx::Painter API.
We now keep the color value as a StyleValue up until we go to paint the
gradient, which makes `currentColor` work, along with any other color
values that can't be immediately converted into a `Gfx::Color` while
parsing.
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)
This was wrong twice making it right... But let's fix that.
The center was being passed as a DevicePixelPoint, but was in fact in
CSS pixels, the size was passed as a Gfx::FloatSize but was in
CSS pixels again. Then we were scaling from device pixels to CSS pixels
when painting which does not need to be done if everything is passed
which the correct scale factors already applied.
These allow you to specify the point were the gradient transitions
from one color to the next (without a transition hint the transition
occurs at the point 50% of the way between the two colors).
There is a little bit of guesswork in this implementation as the
specification left out how hints work with the color stop fixup,
though it appears that they are treated the same as color stops.
This commit moves both the ImageStyleValue and LinearGradientStyleValue
to a common base class of AbstractImageStyleValue. This abstracts
getting the natural_width/height, loading/resolving, and painting
the image.
Now for 'free' you get:
- Linear gradients working with the various background sizing/repeat
properties.
- Linear gradients working as list-markers :^) -- best feature ever!
P.s. This commit is a little large as it's tricky to make this change
incrementally without breaking things.
This implements support for painting linear-gradients in a spec
correct way :^).
Right now it supports:
- Multi-stop gradients
- Color stop fixups
- Using pre-multiplied alpha mixing when required
- Painting gradients at arbitrary angles
It still needs to support:
- Transition hints
- Double position color stops
However what is implemented now seems to be accurate to other
browsers, and covers the most common use cases.
