From 171c07ab4d63b2aee57762eb9ac65834102207b5 Mon Sep 17 00:00:00 2001
From: Neil Hodgson <nyamatongwe@gmail.com>
Date: Mon, 18 Sep 2017 12:24:00 +1000
Subject: Bug [#1885]. Improve scrolling on macOS 10.12.

---
 cocoa/ScintillaView.mm    | 23 +++++++++++++++--------
 doc/ScintillaHistory.html |  4 ++++
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/cocoa/ScintillaView.mm b/cocoa/ScintillaView.mm
index 7891beed8..c19c976f7 100644
--- a/cocoa/ScintillaView.mm
+++ b/cocoa/ScintillaView.mm
@@ -696,20 +696,20 @@ static NSCursor *cursorFromEnum(Window::Cursor cursor) {
 //--------------------------------------------------------------------------------------------------
 
 /**
- * Mouse wheel with command key magnifies text.
- * Enabling this code causes visual garbage to appear when scrolling
- * horizontally on OS X 10.9 with a retina display.
- * Pinch gestures and key commands can be used for magnification.
+ * Implementing scrollWheel makes scrolling work better even if just
+ * calling super.
+ * Mouse wheel with command key may magnify text if enabled.
+ * Pinch gestures and key commands can also be used for magnification.
  */
-#ifdef SCROLL_WHEEL_MAGNIFICATION
 - (void) scrollWheel: (NSEvent *) theEvent {
+#ifdef SCROLL_WHEEL_MAGNIFICATION
 	if (([theEvent modifierFlags] & NSCommandKeyMask) != 0) {
 		mOwner.backend->MouseWheel(theEvent);
-	} else {
-		[super scrollWheel: theEvent];
+		return;
 	}
-}
 #endif
+	[super scrollWheel: theEvent];
+}
 
 //--------------------------------------------------------------------------------------------------
 
@@ -728,6 +728,13 @@ static NSCursor *cursorFromEnum(Window::Cursor cursor) {
 		long lineHeight = mOwner.backend->WndProc(SCI_TEXTHEIGHT, 0, 0);
 		rc.origin.y = roundf(static_cast<XYPOSITION>(rc.origin.y) / lineHeight) * lineHeight;
 	}
+	// Snap to whole points - on retina displays this avoids visual debris
+	// when scrolling horizontally.
+	if ((rc.origin.x > 0) && (NSMaxX(rc) < contentRect.size.width)) {
+		// Only snap for positions inside the document - allow outside
+		// for overshoot.
+		rc.origin.x = roundf(static_cast<XYPOSITION>(rc.origin.x));
+	}
 	return rc;
 }
 
diff --git a/doc/ScintillaHistory.html b/doc/ScintillaHistory.html
index 1b1feb485..b59c4e48a 100644
--- a/doc/ScintillaHistory.html
+++ b/doc/ScintillaHistory.html
@@ -556,6 +556,10 @@
 	<a href="http://sourceforge.net/p/scintilla/bugs/1968/">Bug #1968</a>.
 	</li>
 	<li>
+	On Cocoa, improve scrolling on macOS 10.12.
+	<a href="http://sourceforge.net/p/scintilla/bugs/1885">Bug #1885</a>.
+	</li>
+	<li>
 	On Cocoa, fix line selection by clicking in the margin when scrolled.
 	<a href="http://sourceforge.net/p/scintilla/bugs/1971">Bug #1971</a>.
 	</li>
-- 
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