The `BaseCMapReaderFactory`, `BaseStandardFontDataFactory`, and `BaseWasmFactory` classes are all very similar, and the only difference is really in their respective `fetch` methods.
By have the worker-thread "compute" the complete `filename` it's possible to simplify the `BaseCMapReaderFactory.prototype.fetch` method, which will allow future improvements to all of these classes.
A couple of things to note:
- This code is unused, and it's not even bundled, in the Firefox PDF Viewer.
- In browsers it's unused by default, and worker-thread fetching will always be used when possible since that's more efficient.
*Please note:* For users that provide a custom `CMapReaderFactory` instance when calling `getDocument` this could be a breaking change, however it's unlikely that any such users exist.
(The *internal* format of this data was changed previously in PR 18951, and there hasn't been a single question/complaint about it in well over a year.)
The WebGPU feature hasn't been released yet but it's interesting to see how
we can use it in order to speed up the rendering of some objects.
This patch allows to render mesh patterns using WebGPU.
I didn't see any significant performance improvement on my machine (mac M2)
but it may be different on other platforms.
Given that we "forcibly" set `useWorkerFetch = true` for the MOZCENTRAL build-target there's a small amount of dead code as a result, which we can thus remove during building.
Given that these classes are only used from the "FetchBinaryData" message handler, the `name`/`filename` parameters should never actually be missing and if they are that's a bug elsewhere in the code-base.
Furthermore a missing `name`/`filename` parameter would result in a "nonsense" URL and the actual data fetching would then fail instead, hence keeping this old validation code just doesn't seem necessary.
In PR 20367 the `CompiledFont.prototype.getPathJs` method was changed to return TypedArray data, however the `NOOP` fallback was (likely accidentally) left an empty string.
The compilation of font-paths in PR 20346 was then implemented such that an empty string just happened to be ignored silently, however the assert added in PR 20894 allowed me to spot this return value inconsistency.
*Please note:* Since this only applies to missing or broken glyphs, that wouldn't be rendered anyway, this doesn't show up in reference tests.
Providing one of these parameters is necessary when calling `getDocument`, since otherwise there's nothing to actually load. However, we currently don't enforce that properly and if there's more than one of these parameters provided the behaviour isn't well defined.[1]
The new behaviour is thus, in order:
1. Use the `data` parameter, since the PDF is already available and no additional loading is necessary.
2. Use the `range` parameter, for custom PDF loading (e.g. the Firefox PDF Viewer).
3. Use the `url` parameter, and have the PDF.js library load the PDF with a suitable `networkStream`.
4. Throw an error, since there's no way to load the PDF.
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[1] E.g. if both `data` and `range` is provided, we'd load the document directly (since it's available) and also initialize a pointless `PDFDataTransportStream` instance.
Given that `CompiledFont.prototype.getPathJs` already returns data in the desired TypedArray format, we should be able to directly copy the font-path data which helps shorten the code a little bit (rather than the "manual" handling in PR 20346).
To ensure that this keeps working as expected, a non-production `assert` is added to prevent any future surprises.
After the changes in PR 20197 the code in the `TranslatedFont.prototype.send` method is not all that readable[1] given how it handles e.g. the `charProcOperatorList` data used with Type3 fonts.
Since this is the only spot where `Font.prototype.exportData` is used, it seems much simpler to move the `compileFontInfo` call there and *directly* return the intended data rather than messing with it after the fact.
Finally, while it doesn't really matter, the patch flips the order of the `charProcOperatorList` and `extra` properties throughout the code-base since the former is used with Type3 fonts while the latter (effectively) requires that debugging is enabled.
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[1] I had to re-read it twice, also looking at all the involved methods, in order to convince myself that it's actually correct.
The commit message for the patch in PR 20427 is pretty non-descriptive, being only a single line, however there's a bit more context in https://github.com/mozilla/pdf.js/pull/20427#issue-3597370951 but unfortunately the details there don't really make sense.
Note that the PR only changed main-thread code, but all the links are to worker-thread code!?
The `FontFaceObject` class is only used on the main-thread, and when encountering a broken font we fallback to the built-in font renderer; see 820b70eb25/src/display/font_loader.js (L135-L143)
Hence the `FontFaceObject` class *only* needs a way to set the `disableFontFace` property, however nowhere on the main-thread do we ever update the `bbox` of a font.
This is an old API-parameter that is now unused within the PDF.js project itself, and its description says that it's (partly) being used for "range requests operations".
Note that the `length` API-parameter is used to set the *initial* `contentLength` in various `BasePDFStreamReader` implementations, however it's always overridden by the "Content-Length" header (sent by the server) when that one exists *and* is a valid number. While we currently fallback to the keep the initial `contentLength` otherwise, note however how in that case range requests will always be *disabled* and thus the only spot in the code-base [where `fullReader.contentLength` is necessary](873378b718/src/core/worker.js (L230-L236)) cannot actually be reached.
Hence the only possible reason to use the `length` API-parameter would be for improved progress reporting[1] during streaming of PDF data in rare cases where the "Content-Length" header is missing/invalid, but the user *somehow* has information from another source about the correct `length` of the PDF document.
That situation feels very much like an edge-case, but it's obviously impossible to know if someone is depending on it. However, please note that there's a work-around available for users affected by this removal:
- Implement a `PDFDataRangeTransport` instance together with custom data-fetching[2], since in that case its `length`-parameter will always be used as-is.
Finally, updates various `BasePDFStreamReader` implementations to only set the `_isRangeSupported` field once the headers are available (since previously we'd just overwrite the "initial" value anyway).
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[1] I.e. to avoid the "indeterminate" loadingBar being displayed in the viewer.
[2] This is what e.g. the Firefox PDF Viewer uses.
Currently the `bbox`, `fontMatrix`, and `defaultVMetrics` getters duplicate almost the same code, which we can avoid by adding a new helper method (similar to existing ones for reading numbers and strings).
The added `assert` in the new helper method also caught a bug in how the `defaultVMetrics` length was compiled.
