Qt 6.6 WebAssembly Dev Roadmap

Continued from QTBUG-106637.

Preliminary 6.6 R&D roadmap items, in no particular order:

(Note for external readers: this is a list of topics the Qt for WebAssembly team considers interesting to work on, but includes way more than can be realistically delivered for 6.6)

• Drag and drop improvements
  Investigate if it’s possible to implement a Qt file system engine which gives access to local files.
  Improve dragging into and out of the application.

• WebGPU
  Prototype WebGPU RHI backend.

• Testing
  Continue work on CI auto-testing
  Improve native test coverage (clipboard support, settings, app startup/shutdown)

• qtloader.js
  Rework the current implementation to use modern js. Document public wasm instance API.

• Accessibility
  Continue testing and improving accessibility support. Test with screen readers on the desktop operating systems, with different browsers.

• Resources (QTBUG-74568)
  Enable use of separate resource files to avoid piping resources through the wasm compiler(s)

• Dynamic loading
  Continue implementing support for more use cases.

• Build system options
  Make sure we have (documented) API for overriding all options Qt sets (INITIAL_MEMORY etc)

• Fonts
  Implement native font engine which draws glyphs to a canvas glyph cache using native API.
  Improve font database font indexing (QTBUG-114469)

• Async: prototype support for https://v8.dev/blog/jspi aka emscripten ASYNCIFY=2.

• Look at WebTransport (next-gen web networking). Qt has a WebSockets module, should we have a WebTransport module?

• Look at  Origin private file system  Currently Emscripten provides the file system abstraction, however if we implement a Qt file system engine then OPFS support could be interesting as well. (QTBUG-115695)