The idea with this helper function is that once https://github.com/tc39/proposal-math-clamp/ becomes stable, all its call-sites should then be replaced by the native functionality.
It fixes#5046.
We just generate a mesh for the pattern rectangle where the color of each vertex is computed from the function.
Since the mesh is generated in the worker we don't really take into account the current transform when it's drawn.
That being said, there are maybe some possible improvements in using directly the gpu for the shading creation
which could then take into account the current transform, but it could only work with ps function we can convert
ino wgsl language and simple enough color spaces (gray and rgb).
While `Readable.toWeb` wasn't marked as stable until more recently, the functionality itself has existed since Node.js version `17.0.0`; note https://nodejs.org/api/stream.html#streamreadabletowebstreamreadable-options
Hence the polyfill shouldn't actually be necessary, which is confirmed by the unit-tests passing in Node.js version `20` in GitHub Actions.
The main goal is to remove the eval-based interpreter.
In order to have some good performances, the new parser performs some optimizations
on the AST (similar to the ones in the previous implementation),
and the Wasm compiler generates code for the optimized AST.
For now, in case of errors or unsupported features, the Wasm compiler returns null
and the old interpreter is used as a fallback.
Few things are still missing:
- a wasm-based interpreter using a stack (in case the ps code isn't stack-free);
- a better js implementation in case of disabled wasm.
but they will be added in follow-up patches.
This function only has a single call-site (if we ignore the unit-tests), where the colors are split into separate parameters.
Given that all the color components are modified in the exact same way, it seems easier (and shorter) to pass the colors as-is to `applyOpacity` and have it use `Array.prototype.map()` instead.
This code already has an integration-test, however also having a unit-test shouldn't hurt since those are often easier to run and debug (and it nicely complements the existing `outline` unit-tests).
The patch also makes the following smaller changes to the method itself:
- Avoid creating and parsing an empty Array, when doing the `pageRef` search.
- Use `XRef.prototype.fetch` directly, when walking the parent chain, since the check just above ensures that the value is a Reference.
- Use the `lookupRect` helper when parsing the /BBox entry.
This obviously won't matter in practice, however it seems more "correct" to only extract the necessary number of color components rather than slicing off excess ones at the end.
Since this code is quite old parts of it can also be simplified a little bit by using modern string methods, which removes the need for the `pad` helper function.
