Backport: Bug [#1885]. Improve scrolling on macOS 10.12.

Backport of changeset 6393:711d6bbf62b6.

2 files changed, 19 insertions, 8 deletions

diff --git a/cocoa/ScintillaView.mm b/cocoa/ScintillaView.mm
index f7c9dcf1b..96d212138 100644
--- a/cocoa/ScintillaView.mm
+++ b/cocoa/ScintillaView.mm
@@ -777,21 +777,21 @@ 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];
+}
 
 //--------------------------------------------------------------------------------------------------
 
@@ -811,6 +811,13 @@ 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 f4a061a93..45d0e3255 100644
--- a/doc/ScintillaHistory.html
+++ b/doc/ScintillaHistory.html
@@ -592,6 +592,10 @@
 	<a href="http://sourceforge.net/p/scintilla/bugs/1919/">Bug #1919</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>