Add IME support

.github/FUNDING.yml

@@ -1 +1 @@
-github: [fyne-io, andydotxyz, toaster, Jacalz, changkun]
+github: [fyne-io, andydotxyz, toaster, Jacalz, changkun, dweymouth, lucor]

CHANGELOG.md

@@ -16,7 +16,7 @@ More detailed release notes can be found on the [releases page](https://github.c
 * Reduce calls to C and repeated size checks in painter and driver code
 
 
-## 2.4.2 - 21 November 2023
+## 2.4.2 - 22 November 2023
 
 ### Fixed
 

canvasobject.go

@@ -75,6 +75,18 @@ type Focusable interface {
 	TypedKey(*KeyEvent)
 }
 
+type CursorPositionChangedCallback func(pos Position, size Size)
+
+// Preeditable describes any CanvasObject that can respond to IME inputs.
+// Originally, it should be a method of Focusable, but only a few widgets need PreeditChanged,
+// and adding a method to Focusable will have a big impact on others, so defined as a new interface.
+type Preeditable interface {
+	// PreeditChanged is a hook called by window with IME is on and typed multi-byte characters inputed
+	PreeditChanged(preedit string)
+
+	ReceiveCursorPositionChangedCallback(callback CursorPositionChangedCallback)
+}
+
 // Scrollable describes any CanvasObject that can also be scrolled.
 // This is mostly used to implement the widget.ScrollContainer.
 type Scrollable interface {

internal/driver/common/canvas.go

@@ -191,6 +191,18 @@ func (c *Canvas) Focused() fyne.Focusable {
 	return mgr.Focused()
 }
 
+// Preeditable return the current preeditable object only when focused
+func (c *Canvas) Preeditable() fyne.Preeditable {
+	focused := c.Focused()
+	if focused == nil {
+		return nil
+	}
+	if preeditable, ok := focused.(fyne.Preeditable); ok {
+		return preeditable
+	}
+	return nil
+}
+
 // FocusGained signals to the manager that its content got focus.
 // Valid only on Desktop.
 func (c *Canvas) FocusGained() {

internal/driver/glfw/loop_desktop.go

@@ -11,8 +11,11 @@ import (
 	"github.com/go-gl/glfw/v3.3/glfw"
 )
 
+const GLFW_X11_ONTHESPOT glfw.Hint = 0x00052002
+
 func (d *gLDriver) initGLFW() {
 	initOnce.Do(func() {
+		glfw.InitHint(GLFW_X11_ONTHESPOT, 1) // enable IME callbacks, hint must be set before Init()
 		err := glfw.Init()
 		if err != nil {
 			fyne.LogError("failed to initialise GLFW", err)

internal/driver/glfw/window.go

@@ -805,6 +805,14 @@ func (w *window) processCharInput(char rune) {
 	}
 }
 
+// preedit defines the character with modifiers callback
+// witch is called when character input on IME
+func (w *window) processPreedit(preedit string) {
+	if preeditable := w.canvas.Preeditable(); preeditable != nil {
+		w.QueueEvent(func() { preeditable.PreeditChanged(preedit) })
+	}
+}
+
 func (w *window) processFocused(focus bool) {
 	if focus {
 		if curWindow == nil {

internal/driver/glfw/window_desktop.go

@@ -6,6 +6,7 @@ package glfw
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"image"
 	_ "image/png" // for the icon
 	"runtime"
@@ -677,6 +678,47 @@ func (w *window) charInput(viewport *glfw.Window, char rune) {
 	w.processCharInput(char)
 }
 
+var counterIme int
+
+// IME
+func (w *window) imeStatus(_ *glfw.Window) {
+	counterIme++
+	if preeditable := w.canvas.Preeditable(); preeditable != nil {
+		// This callback function is called by the focused widget and tells the system the exact canvas coordinates
+		// of the text cursor on the window. The system will display an IME Candidate Window with those coordinates
+		preeditable.ReceiveCursorPositionChangedCallback(func(pos fyne.Position, size fyne.Size) {
+			canvasScale := w.canvas.scale
+			w.viewport.SetPreeditCursorRectangle(int(pos.X*canvasScale), int(pos.Y*canvasScale), 100, int(size.Height))
+			w.viewport.UpdatePreeditCursorRectangle()
+		})
+	}
+}
+
+func (w *window) preedit(
+	_ *glfw.Window,
+	preeditCount int,
+	preeditString string,
+	blockCount int,
+	blockSizes string,
+	focusedBlock int,
+	caret int,
+) {
+	w.processPreedit(preeditString)
+}
+
+func (w *window) preeditCandidate(
+	glwin *glfw.Window,
+	candidatesCount int,
+	selectedIndex int,
+	pageStart int,
+	pageSize int,
+) {
+	candidate := glwin.GetPreeditCandidate(selectedIndex)
+	if candidate != nil {
+		fmt.Println("candidates", *candidate)
+	}
+}
+
 func (w *window) focused(_ *glfw.Window, focused bool) {
 	w.processFocused(focused)
 }
@@ -765,11 +807,15 @@ func (w *window) create() {
 		win.SetRefreshCallback(w.refresh)
 		win.SetContentScaleCallback(w.scaled)
 		win.SetCursorPosCallback(w.mouseMoved)
+		win.SetPreeditCallback(w.preedit)
+		win.SetImeStatusCallback(w.imeStatus)
+		win.SetPreeditCandidateCallback(w.preeditCandidate)
 		win.SetMouseButtonCallback(w.mouseClicked)
 		win.SetScrollCallback(w.mouseScrolled)
 		win.SetKeyCallback(w.keyPressed)
 		win.SetCharCallback(w.charInput)
 		win.SetFocusCallback(w.focused)
+		win.SetInputMode(glfw.ImeOwnerDraw, glfw.False)
 
 		w.canvas.detectedScale = w.detectScale()
 		w.canvas.scale = w.calculatedScale()