The C++ text input model used by Windows and Linux currently uses UTF-32. The intention was to facilitate handling of arrow keys, backspace/delete, etc., however since part of what is synchronized with the engine is cursor+selection offsets, and those offsets are defined in terms of UTF-16 code units, this causes very bad interactions with the framework-side model.
This converts to using UTF-16, rather than UTF-32, so that the offsets align with the framework. It also adds surrogate pair handling to the operations that adjust indexes, to avoid breaking surrogate pairs. (Arbitrary grapheme cluster handling is out of scope for this PR; while definitely desirable in the long term, surrogate pair handling is much more critical since improper handling yields invalid UTF-16, which breaks the text field).
This partially fixes https://github.com/flutter/flutter/issues/55014. A framework-side fix is also necessary (since currently both the engine and the framework attempt to handle arrow keys, which is another out-of-scope-for-this-PR issue), but even without the framework fix this dramatically improves the cursor behavior on Windows when there are surrogate pairs somewhere in the string since at least the two sides agree on what indexes mean.
Includes minor plumbing changes to the text input plumbing on Windows so that we're not pointlessly converting from UTF-16 to UTF-32 and then back to UTF-16.
Fixes a few issues with Windows text input:
- Filters out ASCII control characters
- Filters out lead surrogates, which aren't valid UTF-16 on their own so will cause assertion failures if sent to Flutter
- Adds a bandaid fix for a crash due to mismatches in indexing in the C++ and Dart text models. (A better fix would be to use UTF-16 and add surrogate pair handling to deletion and forward/back; that will be a later PR since it has a larger scope.)
Fixes https://github.com/flutter/flutter/issues/54879
The raster cache is critical for good performance. This
enables the cache and provides a GrContext to ScopedFrame
instances so the cache can be efficiently populated.
Small increase in peak GPU memory usage is expected from
this change. Otherwise, no change in behavior expected.
Fixes https://github.com/flutter/flutter/issues/54950
Co-authored-by: David Reveman <reveman@google.com>
16 MiB -> 28 MiB
Same size as what would be used on a 1024x600 display if we
allowed the common engine code to adjust this.
Co-authored-by: David Reveman <reveman@google.com>
