[RDY] win32 ime

[yatli]

wip, does not work yet

wip, partially working.

Almost ready now.

Problems/TODO:

• What is the origin for the rect in SetCursorRect? Treating them as screen coords kind of works, but the relative position inside a control will offset the IME with the cursor.
  • Screen coords work as intended
• It seems that when coords are off by too much (out of screen?), the composition win goes back to the top left of screen, and candidate window jumps between top left and bottom right.
  • This is a TextBox bug. A TextBoxTextInputMethodClient bug.
• Need to detect current locale and handle different IME placement conventions.
• Need a way for the window impl to notify InputMethodManager that IME has been switched -- otherwise TextInputMethodClientRequestedEvent won't fire to register the new IME.
• Composition content support (Let's save it for the next time...)
• Bonus: client-side IME toggle

[kekekeks]

Technically preedit and other advanced features are already in the API:

Avalonia/src/Avalonia.Input/TextInput/ITextInputMethodClient.cs

Lines 27 to 51 in d2347bf

	bool SupportsPreedit { get; }
	/// <summary>
	/// Sets the non-committed input string
	/// </summary>
	void SetPreeditText(string text);
	/// <summary>
	/// Indicates if text input client is capable of providing the text around the cursor
	/// </summary>
	bool SupportsSurroundingText { get; }
	/// <summary>
	/// Returns the text around the cursor, usually the current paragraph, the cursor position inside that text and selection start position
	/// </summary>
	TextInputMethodSurroundingText SurroundingText { get; }
	/// <summary>
	/// Should be fired when surrounding text changed
	/// </summary>
	event EventHandler SurroundingTextChanged;
	/// <summary>
	/// Returns the text before the cursor. Must return a non-empty string if cursor is not at the beginning of the text entry
	/// </summary>
	string TextBeforeCursor { get; }
	/// <summary>
	/// Returns the text before the cursor. Must return a non-empty string if cursor is not at the end of the text entry
	/// </summary>
	string TextAfterCursor { get; }

but we have this chicken and egg problem: platform code doesn't handle preedit and textbox doesn't support it as well.

[kekekeks]

I guess we need some control in the control catalog or sandbox to test the platform support.

[kekekeks]

Why exactly do we need this? Is it needed to handle keyboard layout switch between basic and IME-enabled languages?

[kekekeks]

I'm not sure if that should be handled on the xplat layer though. I'd expect that state to be tracked by the platform code that encapsulates such switches.

[yatli]

Not sure how other users do this, but for me I heavily rely on win+space to switch between en/zh on the fly.
The ime manager queries client capabilities when it gets focus (or init?), but doesn't handle IME switch when the control is focused.

[kekekeks]

Well, I'd expect the WindowImpl.cs to always have an active Imm32InputMethod instance (just like X11Window does) that maintains its state rather than going through the requery process. Your approach also adds more ties between input method handling and toplevels while we are kinda planning to add built-in OSK support.

[yatli]

WindowImpl always have that. InputMethodManager doesn't.

[kekekeks]

The initial idea was that InputMethodManager synchronizes the control with the native window implementation. The native window implementation is supposed to keep track of what was previously passed to it rather than requery that information on demand.

[yatli]

I see. Maybe it's possible to put the mutable states in IMM32InputMethod.

[Mikolaytis]

Good Job! can't wait to see this merged!

[Mikolaytis]

I've merged this(with minor tweaks) to my private fork and our QA will test this until the weekend. I will notify about the result. For the first look - everything is perfect.

[Mikolaytis]

We are missing some things:

1. Ability to toggle IME on/off on a InputElement like WPF's InputMethodEnabled
2. IME is not applying FontSize to intermediate input.
3. No way to configure margin/padding or offset of intermediate input.
4. No way to disable intermediate input and/or candidates list.

Possible Improvement:
Currently TextInput event raised only by WM_CHAR windows message. To get the best IME support, like in chromium we should listen to all of the IME messages WM_IME_STARTCOMPOSITION,WM_IME_COMPOSITION,WM_IME_ENDCOMPOSITION and handle them properly, like WPF do.

[Mikolaytis]

Also here is a some bugs:

1. IME is not working after any dialog window launch(OpenFileDialog/SaveFiledialog is working fine).
2. On Windows 10 emoji panel position is not updated at all. Only the first show is in correct position. To update the position again - you should switch to another app and back.

[maxkatz6]

This PR was completed with that one #7007
Thanks @yatli and @Mikolaytis