feat: Windows (CF_DIB) and macOS (AppleScript) clipboard image sync

internal/clipboard/clipboard_windows.go

@@ -137,3 +137,83 @@ func lockAndWrite(h uintptr, data []uint16) bool {
 	copy(dst, data)
 	return true
 }
+
+// ReadImage returns the clipboard image (CF_DIB) encoded as PNG.
+func (c *windowsClipboard) ReadImage() (string, []byte, error) {
+	r1, _, _ := procOpenClipboard.Call(0)
+	if r1 == 0 {
+		return "", nil, ErrNoImage
+	}
+	defer func() { _, _, _ = procCloseClipboard.Call() }()
+
+	h, _, _ := procGetClipboardData.Call(uintptr(cfDIB))
+	if h == 0 {
+		return "", nil, ErrNoImage
+	}
+
+	size, _, _ := procGlobalSize.Call(h)
+	if size == 0 {
+		return "", nil, ErrNoImage
+	}
+
+	p, _, _ := procGlobalLock.Call(h)
+	if p == 0 {
+		return "", nil, ErrNoImage
+	}
+	defer func() { _, _, _ = procGlobalUnlock.Call(h) }()
+
+	// Copy the DIB bytes out of the global block before parsing.
+	ptr := unsafe.Add(unsafe.Pointer(nil), p)
+	raw := unsafe.Slice((*byte)(ptr), size)
+	dib := make([]byte, size)
+	copy(dib, raw)
+
+	pngBytes, err := dibToPNG(dib)
+	if err != nil {
+		return "", nil, err
+	}
+	return "image/png", pngBytes, nil
+}
+
+// WriteImage writes a PNG image to the clipboard as a CF_DIB.
+func (c *windowsClipboard) WriteImage(mime string, data []byte) error {
+	if mime != "" && mime != "image/png" {
+		return fmt.Errorf("clipboard: unsupported image mime %q (only PNG)", mime)
+	}
+	dib, err := pngToDIB(data)
+	if err != nil {
+		return fmt.Errorf("clipboard: decode image: %w", err)
+	}
+
+	r1, _, err2 := procOpenClipboard.Call(0)
+	if r1 == 0 {
+		return fmt.Errorf("clipboard write image: OpenClipboard: %w", err2)
+	}
+	defer func() { _, _, _ = procCloseClipboard.Call() }()
+
+	if r1, _, err2 = procEmptyClipboard.Call(); r1 == 0 {
+		return fmt.Errorf("clipboard write image: EmptyClipboard: %w", err2)
+	}
+
+	h, _, err2 := procGlobalAlloc.Call(0, uintptr(len(dib)))
+	if h == 0 {
+		return fmt.Errorf("clipboard write image: GlobalAlloc: %w", err2)
+	}
+
+	p, _, _ := procGlobalLock.Call(h)
+	if p == 0 {
+		_, _, _ = procGlobalFree.Call(h)
+		return fmt.Errorf("clipboard write image: GlobalLock failed")
+	}
+	ptr := unsafe.Add(unsafe.Pointer(nil), p)
+	dst := unsafe.Slice((*byte)(ptr), len(dib))
+	copy(dst, dib)
+	_, _, _ = procGlobalUnlock.Call(h)
+
+	if r1, _, err2 = procSetClipboardData.Call(uintptr(cfDIB), h); r1 == 0 {
+		_, _, _ = procGlobalFree.Call(h)
+		return fmt.Errorf("clipboard write image: SetClipboardData: %w", err2)
+	}
+	// Windows now owns the handle.
+	return nil
+}