Bug [#2094]. gtk: Accessible: use the built-in character position cache

It's quite a lot faster even after trying and optimizing the custom
version, and it makes the code simpler.

Also improve ByteOffsetFromCharacterOffset() to make use of the cache,
making it drastically faster.

3 files changed, 19 insertions, 25 deletions

diff --git a/gtk/ScintillaGTK.cxx b/gtk/ScintillaGTK.cxx
index c98fde84a..5ee3b865a 100644
--- a/gtk/ScintillaGTK.cxx
+++ b/gtk/ScintillaGTK.cxx
@@ -867,7 +867,7 @@ sptr_t ScintillaGTK::WndProc(unsigned int iMessage, uptr_t wParam, sptr_t lParam
 			if (accessible) {
 				ScintillaGTKAccessible *sciAccessible = ScintillaGTKAccessible::FromAccessible(accessible);
 				if (sciAccessible) {
-					sciAccessible->SetAccessibility();
+					sciAccessible->SetAccessibility(accessibilityEnabled);
 				}
 			}
 			break;
diff --git a/gtk/ScintillaGTKAccessible.cxx b/gtk/ScintillaGTKAccessible.cxx
index 5f2979894..714fde10d 100644
--- a/gtk/ScintillaGTKAccessible.cxx
+++ b/gtk/ScintillaGTKAccessible.cxx
@@ -163,6 +163,7 @@ ScintillaGTKAccessible::ScintillaGTKAccessible(GtkAccessible *accessible_, GtkWi
 		sci(ScintillaGTK::FromWidget(widget_)),
 		deletionLengthChar(0),
 		old_pos(-1) {
+	SetAccessibility(true);
 	g_signal_connect(widget_, "sci-notify", G_CALLBACK(SciNotify), this);
 }
 
@@ -866,10 +867,12 @@ void ScintillaGTKAccessible::NotifyReadOnly() {
 #endif
 }
 
-void ScintillaGTKAccessible::SetAccessibility() {
+void ScintillaGTKAccessible::SetAccessibility(bool enabled) {
 	// Called by ScintillaGTK when application has enabled or disabled accessibility
-	character_offsets.resize(0);
-	character_offsets.push_back(0);
+	if (enabled)
+		sci->pdoc->AllocateLineCharacterIndex(SC_LINECHARACTERINDEX_UTF32);
+	else
+		sci->pdoc->ReleaseLineCharacterIndex(SC_LINECHARACTERINDEX_UTF32);
 }
 
 void ScintillaGTKAccessible::Notify(GtkWidget *, gint, SCNotification *nt) {
@@ -877,13 +880,6 @@ void ScintillaGTKAccessible::Notify(GtkWidget *, gint, SCNotification *nt) {
 		return;
 	switch (nt->nmhdr.code) {
 		case SCN_MODIFIED: {
-			if (nt->modificationType & (SC_MOD_INSERTTEXT | SC_MOD_DELETETEXT)) {
-				// invalidate character offset cache if applicable
-				const Sci::Line line = sci->pdoc->LineFromPosition(nt->position);
-				if (character_offsets.size() > static_cast<size_t>(line + 1)) {
-					character_offsets.resize(line + 1);
-				}
-			}
 			if (nt->modificationType & SC_MOD_INSERTTEXT) {
 				int startChar = CharacterOffsetFromByteOffset(nt->position);
 				int lengthChar = sci->pdoc->CountCharacters(nt->position, nt->position + nt->length);
diff --git a/gtk/ScintillaGTKAccessible.h b/gtk/ScintillaGTKAccessible.h
index 2c39d5257..00570acce 100644
--- a/gtk/ScintillaGTKAccessible.h
+++ b/gtk/ScintillaGTKAccessible.h
@@ -18,9 +18,6 @@ private:
 	GtkAccessible *accessible;
 	ScintillaGTK *sci;
 
-	// cache holding character offset for each line start, see CharacterOffsetFromByteOffset()
-	std::vector<Sci::Position> character_offsets;
-
 	// cached length of the deletion, in characters (see Notify())
 	int deletionLengthChar;
 	// local state for comparing
@@ -37,6 +34,16 @@ private:
 	}
 
 	Sci::Position ByteOffsetFromCharacterOffset(Sci::Position startByte, int characterOffset) {
+		if (characterOffset > 0) {
+			// Try and reduce the range by reverse-looking into the character offset cache
+			Sci::Line lineStart = sci->pdoc->LineFromPosition(startByte);
+			Sci::Position posStart = sci->pdoc->IndexLineStart(lineStart, SC_LINECHARACTERINDEX_UTF32);
+			Sci::Line line = sci->pdoc->LineFromPositionIndex(posStart + characterOffset, SC_LINECHARACTERINDEX_UTF32);
+			if (line != lineStart) {
+				startByte += sci->pdoc->LineStart(line) - sci->pdoc->LineStart(lineStart);
+				characterOffset -= sci->pdoc->IndexLineStart(line, SC_LINECHARACTERINDEX_UTF32) - posStart;
+			}
+		}
 		Sci::Position pos = sci->pdoc->GetRelativePosition(startByte, characterOffset);
 		if (pos == INVALID_POSITION) {
 			// clamp invalid positions inside the document
@@ -55,17 +62,8 @@ private:
 
 	Sci::Position CharacterOffsetFromByteOffset(Sci::Position byteOffset) {
 		const Sci::Line line = sci->pdoc->LineFromPosition(byteOffset);
-		if (character_offsets.size() <= static_cast<size_t>(line)) {
-			if (character_offsets.empty())
-				character_offsets.push_back(0);
-			for (Sci::Position i = character_offsets.size(); i <= line; i++) {
-				const Sci::Position start = sci->pdoc->LineStart(i - 1);
-				const Sci::Position end = sci->pdoc->LineStart(i);
-				character_offsets.push_back(character_offsets[i - 1] + sci->pdoc->CountCharacters(start, end));
-			}
-		}
 		const Sci::Position lineStart = sci->pdoc->LineStart(line);
-		return character_offsets[line] + sci->pdoc->CountCharacters(lineStart, byteOffset);
+		return sci->pdoc->IndexLineStart(line, SC_LINECHARACTERINDEX_UTF32) + sci->pdoc->CountCharacters(lineStart, byteOffset);
 	}
 
 	void CharacterRangeFromByteRange(Sci::Position startByte, Sci::Position endByte, int *startChar, int *endChar) {
@@ -135,7 +133,7 @@ public:
 	// So ScintillaGTK can notify us
 	void ChangeDocument(Document *oldDoc, Document *newDoc);
 	void NotifyReadOnly();
-	void SetAccessibility();
+	void SetAccessibility(bool enabled);
 
 	// Helper GtkWidget methods
 	static AtkObject *WidgetGetAccessibleImpl(GtkWidget *widget, AtkObject **cache, gpointer widget_parent_class);