Ensure page and step clicks on horizontal scroll bar do not overshoot document width.

2 files changed, 28 insertions, 12 deletions

diff --git a/doc/ScintillaHistory.html b/doc/ScintillaHistory.html
index c14fcc59a..5b6b21158 100644
--- a/doc/ScintillaHistory.html
+++ b/doc/ScintillaHistory.html
@@ -601,6 +601,9 @@
 	On Win32 implement horizontal scrolling mouse wheel.
 	<a href="https://sourceforge.net/p/scintilla/feature-requests/1450/">Feature #1450</a>.
 	</li>
+	<li>
+	On Win32 ensure page and step clicks on horizontal scroll bar do not overshoot document width.
+	</li>
     </ul>
     <h3>
        <a href="https://www.scintilla.org/scintilla530.zip">Release 5.3.0</a>
diff --git a/win32/ScintillaWin.cxx b/win32/ScintillaWin.cxx
index 9f1cbe53f..5f989b781 100644
--- a/win32/ScintillaWin.cxx
+++ b/win32/ScintillaWin.cxx
@@ -276,6 +276,11 @@ public:
 	}
 };
 
+struct HorizontalScrollRange {
+	int pageWidth;
+	int documentWidth;
+};
+
 }
 
 namespace Scintilla::Internal {
@@ -404,6 +409,8 @@ class ScintillaWin :
 	void UpdateSystemCaret() override;
 	void SetVerticalScrollPos() override;
 	void SetHorizontalScrollPos() override;
+	void HorizontalScrollToClamped(int xPos);
+	HorizontalScrollRange GetHorizontalScrollRange() const;
 	bool ModifyScrollBars(Sci::Line nMax, Sci::Line nPage) override;
 	void NotifyChange() override;
 	void NotifyFocus(bool focus) override;
@@ -2368,6 +2375,20 @@ bool ScintillaWin::ChangeScrollRange(int nBar, int nMin, int nMax, UINT nPage) n
 	return false;
 }
 
+void ScintillaWin::HorizontalScrollToClamped(int xPos) {
+	const HorizontalScrollRange range = GetHorizontalScrollRange();
+	HorizontalScrollTo(std::clamp(xPos, 0, range.documentWidth - range.pageWidth + 1));
+}
+
+HorizontalScrollRange ScintillaWin::GetHorizontalScrollRange() const {
+	const PRectangle rcText = GetTextRectangle();
+	int pageWidth = static_cast<int>(rcText.Width());
+	const int horizEndPreferred = std::max({ scrollWidth, pageWidth - 1, 0 });
+	if (!horizontalScrollBarVisible || Wrapping())
+		pageWidth = horizEndPreferred + 1;
+	return { pageWidth, horizEndPreferred };
+}
+
 bool ScintillaWin::ModifyScrollBars(Sci::Line nMax, Sci::Line nPage) {
 	if (!IsVisible()) {
 		return false;
@@ -2380,15 +2401,10 @@ bool ScintillaWin::ModifyScrollBars(Sci::Line nMax, Sci::Line nPage) {
 	if (ChangeScrollRange(SB_VERT, 0, static_cast<int>(vertEndPreferred), static_cast<unsigned int>(nPage))) {
 		modified = true;
 	}
-
-	const PRectangle rcText = GetTextRectangle();
-	int pageWidth = static_cast<int>(rcText.Width());
-	const int horizEndPreferred = std::max({scrollWidth, pageWidth - 1, 0});
-	if (!horizontalScrollBarVisible || Wrapping())
-		pageWidth = horizEndPreferred + 1;
-	if (ChangeScrollRange(SB_HORZ, 0, horizEndPreferred, pageWidth)) {
+	const HorizontalScrollRange range = GetHorizontalScrollRange();
+	if (ChangeScrollRange(SB_HORZ, 0, range.documentWidth, range.pageWidth)) {
 		modified = true;
-		if (scrollWidth < pageWidth) {
+		if (scrollWidth < range.pageWidth) {
 			HorizontalScrollTo(0);
 		}
 	}
@@ -3231,9 +3247,6 @@ void ScintillaWin::HorizontalScrollMessage(WPARAM wParam) {
 		break;
 	case SB_PAGEDOWN:
 		xPos += pageWidth;
-		if (xPos > scrollWidth - rcText.Width()) {	// Hit the end exactly
-			xPos = scrollWidth - static_cast<int>(rcText.Width());
-		}
 		break;
 	case SB_TOP:
 		xPos = 0;
@@ -3253,7 +3266,7 @@ void ScintillaWin::HorizontalScrollMessage(WPARAM wParam) {
 		}
 		break;
 	}
-	HorizontalScrollTo(xPos);
+	HorizontalScrollToClamped(xPos);
 }
 
 /**