This commit substantially reworks the `pathfinder_gpu` API to better support
modern APIs like Metal. It should open the door to `gfx-rs`, `wgpu`, Vulkan,
and D3D12 backends relatively straightforwardly.
A new example, `canvas_metal_minimal`, has been added.
Note that the new Metal shaders require a patched version of `spirv-cross` to
build properly. An upstream patch is forthcoming.
The Metal shaders are checked into the repository for convenience, but they
should not be directly edited. Instead, edit the corresponding GLSL shader in
the top-level `shaders/` directory, and rerun `make` in there.
distance-to-edge for stencil analytic antialiasing.
This improves the rendering quality of stencil AAA significantly.
Additionally, this adds an approximation of Core Graphics' (macOS')
defringing filter.
Closes#73.
This doesn't break meshes the way the previous "discard if too thin"
code did. It fixes several issues observed on Wikipedia when using
Pathfinder in Firefox.
Closes#72.
The new `vXDist` values *can* be deduced simply from the `vUV` values
and first-order derivatives thereof, and therefore they're technically
redundant. However, calculating them in this way increases the
complexity and ALU load in the fragment shader. It's simpler to just
compute the additional values in the vertex shader and use
interpolation.
technique similar to the new MCAA.
This new technique simplifies the code significantly by unifying lines,
curves, and transformed curves. Blog posts forthcoming.
approximation of area based on approximate first-order line distance.
This enables support for full affine transforms in MCAA. It also greatly
simplifies the shader and reduces the amount of work that the GPU needs
to do for fragment shading.
Experimental testing has shown the area approximation to be accurate to
about 4%.
This removes a whole lot of code from `pathfinder_path_utils`. Hopefully
the remaining code can go upstream.
These changes regress quality of stroke widths for cubic curves, because
they move fill-to-stroke conversion before cubic-to-quadratic
conversion. To fix that, we will need to recursively subdivide when
doing fill-to-stroke conversion.
enable early Z for SVG.
Additionally, this switches the B-quad patches for XCAA to be convex
hulls instead of bounding boxes, reducing fragment shader load.
This is a large speedup for the Ghostscript tiger demo: 5x or more.
Closes#33.
ECAA algorithm for multicolor SVG.
This is much faster than both Skia and the previous XCAA algorithm
while maintaining slightly higher quality than the latter.
There are a couple of known issues:
* Vertical inflection points of hairlines with very steep slopes can
become very light or even drop out occasionally. I suspect this is due
to floating point error.
* Rarely, single columns of pixels can disappear from a mesh. Cause TBD.
Besides these bugs, this technique can be cleaned up and probably made
faster, but it's a sizable improvement as is.
We now implement stem darkening (also known as font dilation) like
macOS and FreeType under certain configurations. This pushes out font
outlines along their normals slightly in order to make small text easier
to read. This is especially important when performing gamma correction,
as otherwise text can end up too light.
Because the stem darkening is implemented in the vertex shader, it can
easily break the mesh. Therefore, I needed to implement a new rendering
mode that does not use the mesh. It's a variant of ECAA, and for
clarity's sake I've renamed the related antialiasing methods:
* MCAA stands for "mesh coverage antialiasing" and is the new name for
what was called "ECAA" prior to this patch.
* ECAA now stands for "edge coverage antialiasing". It does not use the
mesh but rather computes winding numbers from scratch for every pixel.
Surprisingly, despite being worse asymptotically, this usually ends up
being faster than MCAA at small font sizes, presumably because there are
fewer vertices to transform.
* XCAA, "exact coverage antialiasing" is a generic term that refers to
both ECAA and MCAA. References to ECAA have been changed to XCAA as
needed.
Patrick Walton