Feature [feature-requests:#1304] Avoid unnecessary IME caret movement.

2 files changed, 28 insertions, 7 deletions

diff --git a/doc/ScintillaHistory.html b/doc/ScintillaHistory.html
index 00fca60a6..f512a01bc 100644
--- a/doc/ScintillaHistory.html
+++ b/doc/ScintillaHistory.html
@@ -570,6 +570,10 @@
 	properties like user.shortcuts.
 	<a href="https://sourceforge.net/p/scintilla/feature-requests/1317/">Feature #1317</a>.
 	</li>
+	<li>
+	Avoid unnecessary IME caret movement on Win32.
+	<a href="https://sourceforge.net/p/scintilla/feature-requests/1304/">Feature #1304</a>.
+	</li>
     </ul>
     <h3>
        <a href="https://www.scintilla.org/scite421.zip">Release 4.2.1</a>
diff --git a/win32/ScintillaWin.cxx b/win32/ScintillaWin.cxx
index 98ea15cea..d72f1958b 100644
--- a/win32/ScintillaWin.cxx
+++ b/win32/ScintillaWin.cxx
@@ -1122,15 +1122,32 @@ sptr_t ScintillaWin::HandleCompositionInline(uptr_t, sptr_t lParam) {
 			i += ucWidth;
 		}
 
-		// Move IME caret from current last position to imeCaretPos.
-		const int imeEndToImeCaretU16 = imc.GetImeCaretPos() - static_cast<unsigned int>(wcs.size());
-		const Sci::Position imeCaretPosDoc = pdoc->GetRelativePositionUTF16(CurrentPosition(), imeEndToImeCaretU16);
+		// Japanese IME after pressing Tab replaces input string with first candidate item (target string);
+		// when selecting other candidate item, previous item will be replaced with current one.
+		// After candidate item been added, it's looks like been full selected, it's better to keep caret
+		// at end of "selection" (end of input) instead of jump to beginning of input ("selection").
+		const bool onlyTarget = std::all_of(imeIndicator.begin(), imeIndicator.end(), [](int i) noexcept {
+			return i == SC_INDICATOR_TARGET;
+		});
+		if (!onlyTarget) {
+			// CS_NOMOVECARET: keep caret at beginning if composition string which already moved in InsertCharacter().
+			// GCS_CURSORPOS: current caret position is provided by IME.
+			Sci::Position imeEndToImeCaretU16 = -static_cast<Sci::Position>(wcs.size());
+			if (!(lParam & CS_NOMOVECARET) && (lParam & GCS_CURSORPOS)) {
+				imeEndToImeCaretU16 += imc.GetImeCaretPos();
+			}
+			if (imeEndToImeCaretU16 != 0) {
+				// Move back IME caret from current last position to imeCaretPos.
+				const Sci::Position currentPos = CurrentPosition();
+				const Sci::Position imeCaretPosDoc = pdoc->GetRelativePositionUTF16(currentPos, imeEndToImeCaretU16);
 
-		MoveImeCarets(- CurrentPosition() + imeCaretPosDoc);
+				MoveImeCarets(-currentPos + imeCaretPosDoc);
 
-		if (std::find(imeIndicator.begin(), imeIndicator.end(), SC_INDICATOR_TARGET) != imeIndicator.end()) {
-			// set candidate window left aligned to beginning of target string.
-			SetCandidateWindowPos();
+				if (std::find(imeIndicator.begin(), imeIndicator.end(), SC_INDICATOR_TARGET) != imeIndicator.end()) {
+					// set candidate window left aligned to beginning of target string.
+					SetCandidateWindowPos();
+				}
+			}
 		}
 
 		if (KoreanIME()) {