Add better scroll wheel support and option to disable acceleration

macOS applies a acceleration to the mouse scroll wheel which is often
frustrating to use. In particular, a single click on the scroll wheel
generates a fractional scroll, which doesn't do anything in MacVim as it
scrolls by line. Fix this by forcing each scroll event to scroll at
least one line (this is configurable to be higher, or 0 which means use
the old behavior).

Also add an option to simply turn off acceleration and scroll a fixed
number of lines.

Also, fix horizontal scrolling using mouse wheel. In macOS, the way to
scroll horizontally using a normal wheel is to hold Shift key and
scroll, and the OS will convert that to a horizontal scroll event.
However, we were sending the shift modifier to Vim as well, which
interprets it as <S-ScrollWheelRight> which is not what we want (this
scrolls a whole page). We manually remove the shift modifier when we
detect this. It does mean there's functionally no way to send
shift-scroll wheel events to Vim, but it is ok, as macOS generally works
this way and it's consistent with how native GUI apps work.

Author: ychin

runtime/doc/gui_mac.txt

@@ -283,8 +283,6 @@ as general information regarding macOS user defaults.
 Here is a list of relevant dictionary entries:
 
 KEY				VALUE ~
-*MMAllowForceClickLookUp*	use Force click for data lookup instead of
-				<ForceClick> [bool]
 *MMCellWidthMultiplier*		width of a normal glyph in em units [float]
 *MMCmdLineAlignBottom*		Pin command-line to bottom of MacVim [bool]
 *MMDialogsTrackPwd*		open/save dialogs track the Vim pwd [bool]
@@ -307,7 +305,6 @@ KEY				VALUE ~
 *MMTitlebarAppearsTransparent*	enable a transparent titlebar [bool]
 *MMAppearanceModeSelection*	dark mode selection (|macvim-dark-mode|)[bool]
 *MMRendererClipToRow*		clip tall characters to the row they are on [bool]
-*MMScrollOneDirectionOnly*	scroll along one axis only when using trackpad [bool]
 *MMSmoothResize*		allow smooth resizing of MacVim window [bool]
 *MMShareFindPboard*		share search text to Find Pasteboard [bool]
 *MMTextInsetBottom*		text area offset in pixels [int]
@@ -316,12 +313,22 @@ KEY				VALUE ~
 *MMTextInsetTop*		text area offset in pixels [int]
 *MMTexturedWindow*		use brushed metal window (Tiger only) [bool]
 *MMTranslateCtrlClick*		interpret ctrl-click as right-click [bool]
-*MMUseMouseTime*		use mousetime to detect multiple clicks [bool]
 *MMVerticalSplit*		files open in vertical splits [bool]
 *MMZoomBoth*			zoom button maximizes both directions [bool]
 *MMUpdaterPrereleaseChannel*	opt-in to pre-release software update [bool]
 *MMShowWhatsNewOnStartup*	show "What's New" after updating to new version [bool]
 
+Mouse / Trackpad ~
+*MMScrollOneDirectionOnly*	scroll along one axis only when using trackpad [bool]
+*MMAllowForceClickLookUp*	use Force click for data lookup instead of
+				<ForceClick> [bool]
+*MMMouseWheelDisableAcceleration* disable OS scroll wheel acceleration [bool]
+*MMMouseWheelNumLines*		how many lines to scroll when scroll wheel
+				acceleration is turned off [int]
+*MMMouseWheelMinLines*		min number of lines to scroll per scroll wheel
+				click when acceleration is on [int]
+*MMUseMouseTime*		use mousetime to detect multiple clicks [bool]
+
 Tabs ~
 *MMTabColorsMode*		use default/auto/colorscheme for tab colors [int]
 *MMWindowUseTabBackgroundColor*	use tabs background fill color as window color [bool]

src/MacVim/Base.lproj/Preferences.xib

@@ -573,11 +573,11 @@
             <point key="canvasLocation" x="137.5" y="478.5"/>
         </customView>
         <customView id="Bnq-Nx-GJH" userLabel="Input">
-            <rect key="frame" x="0.0" y="0.0" width="483" height="110"/>
+            <rect key="frame" x="0.0" y="0.0" width="483" height="155"/>
             <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
             <subviews>
                 <customView id="DAP-Yi-QU0" userLabel="Trackpad">
-                    <rect key="frame" x="20" y="72" width="433" height="18"/>
+                    <rect key="frame" x="20" y="117" width="433" height="18"/>
                     <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
                     <subviews>
                         <textField focusRingType="none" verticalHuggingPriority="750" horizontalCompressionResistancePriority="250" id="f18-Wr-EgZ">
@@ -604,11 +604,11 @@
                     </subviews>
                 </customView>
                 <customView id="GZa-RH-fza" userLabel="Mouse">
-                    <rect key="frame" x="20" y="46" width="433" height="18"/>
+                    <rect key="frame" x="20" y="46" width="433" height="63"/>
                     <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
                     <subviews>
                         <textField focusRingType="none" verticalHuggingPriority="750" horizontalCompressionResistancePriority="250" id="3Tx-8j-zQR">
-                            <rect key="frame" x="-2" y="0.0" width="187" height="17"/>
+                            <rect key="frame" x="-2" y="45" width="187" height="17"/>
                             <autoresizingMask key="autoresizingMask" flexibleMinY="YES"/>
                             <textFieldCell key="cell" sendsActionOnEndEditing="YES" alignment="right" title="Mouse:" id="imK-Tr-YuD">
                                 <font key="font" metaFont="system"/>
@@ -617,7 +617,7 @@
                             </textFieldCell>
                         </textField>
                         <button id="RLs-2Z-8PJ" userLabel="Ctrl-click as right-click">
-                            <rect key="frame" x="189" y="-1" width="199" height="18"/>
+                            <rect key="frame" x="189" y="44" width="199" height="18"/>
                             <autoresizingMask key="autoresizingMask" flexibleMinY="YES"/>
                             <buttonCell key="cell" type="check" title="Treat Ctrl-click as right-click" bezelStyle="regularSquare" imagePosition="left" alignment="left" inset="2" id="PYG-cd-wzL" userLabel="Ctrl-click as right-click">
                                 <behavior key="behavior" changeContents="YES" doesNotDimImage="YES" lightByContents="YES"/>
@@ -627,6 +627,43 @@
                                 <binding destination="58" name="value" keyPath="values.MMTranslateCtrlClick" id="ZMh-R3-AYN"/>
                             </connections>
                         </button>
+                        <button id="8rY-bA-ZQt">
+                            <rect key="frame" x="189" y="26" width="224" height="18"/>
+                            <autoresizingMask key="autoresizingMask" flexibleMinY="YES"/>
+                            <buttonCell key="cell" type="check" title="Disable scroll wheel acceleration" bezelStyle="regularSquare" imagePosition="left" alignment="left" inset="2" id="fRx-Gy-P0M">
+                                <behavior key="behavior" changeContents="YES" doesNotDimImage="YES" lightByContents="YES"/>
+                                <font key="font" metaFont="system"/>
+                            </buttonCell>
+                            <connections>
+                                <binding destination="58" name="value" keyPath="values.MMMouseWheelDisbleAcceleration" id="899-jt-taC"/>
+                            </connections>
+                        </button>
+                        <textField focusRingType="none" verticalHuggingPriority="750" horizontalCompressionResistancePriority="250" id="SqW-DB-w7i">
+                            <rect key="frame" x="210" y="3" width="109" height="17"/>
+                            <autoresizingMask key="autoresizingMask" flexibleMinY="YES"/>
+                            <textFieldCell key="cell" sendsActionOnEndEditing="YES" alignment="left" title="Lines to scroll:" id="w03-Ox-2xg">
+                                <font key="font" metaFont="system"/>
+                                <color key="textColor" name="controlTextColor" catalog="System" colorSpace="catalog"/>
+                                <color key="backgroundColor" name="controlColor" catalog="System" colorSpace="catalog"/>
+                            </textFieldCell>
+                            <connections>
+                                <binding destination="58" name="enabled" keyPath="values.MMMouseWheelDisbleAcceleration" id="Mzw-pC-FbR"/>
+                            </connections>
+                        </textField>
+                        <textField focusRingType="none" verticalHuggingPriority="750" id="Zpw-eU-7d1">
+                            <rect key="frame" x="305" y="1" width="32" height="21"/>
+                            <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
+                            <textFieldCell key="cell" scrollable="YES" lineBreakMode="clipping" selectable="YES" editable="YES" sendsActionOnEndEditing="YES" state="on" borderStyle="bezel" drawsBackground="YES" id="Vwr-3s-VFd">
+                                <numberFormatter key="formatter" formatterBehavior="default10_4" numberStyle="decimal" formatWidth="-1" minimumIntegerDigits="1" maximumIntegerDigits="2000000000" maximumFractionDigits="3" id="NEj-vx-0Qo"/>
+                                <font key="font" metaFont="system"/>
+                                <color key="textColor" name="controlTextColor" catalog="System" colorSpace="catalog"/>
+                                <color key="backgroundColor" name="textBackgroundColor" catalog="System" colorSpace="catalog"/>
+                            </textFieldCell>
+                            <connections>
+                                <binding destination="58" name="enabled" keyPath="values.MMMouseWheelDisbleAcceleration" id="i3X-ti-Cv8"/>
+                                <binding destination="58" name="value" keyPath="values.MMMouseWheelNumLines" id="ecJ-lb-ghs"/>
+                            </connections>
+                        </textField>
                     </subviews>
                 </customView>
                 <customView id="aUx-jX-mJJ" userLabel="Scrolling">

src/MacVim/MMAppController.m

@@ -217,6 +217,9 @@ + (void)registerDefaults
         [NSNumber numberWithBool:YES],    MMUseInlineImKey,
 #endif // INCLUDE_OLD_IM_CODE
         [NSNumber numberWithBool:NO],     MMSuppressTerminationAlertKey,
+        [NSNumber numberWithBool:NO],     MMMouseWheelDisableAccelerationKey,
+        [NSNumber numberWithInt:1],       MMMouseWheelMinLinesKey,
+        [NSNumber numberWithInt:3],       MMMouseWheelNumLinesKey,
         [NSNumber numberWithBool:YES],    MMNativeFullScreenKey,
         [NSNumber numberWithDouble:0.0],  MMFullScreenFadeTimeKey,
         [NSNumber numberWithBool:NO],     MMNonNativeFullScreenShowMenuKey,

src/MacVim/MMTextViewHelper.m

@@ -312,15 +312,15 @@ - (void)doCommandBySelector:(SEL)sel
     else interpretKeyEventsSwallowedKey = NO;
 }
 
-- (void)scrollWheel:(NSEvent *)event
+- (void)calcScrollWheelDeltas:(NSEvent *)event x:(float *)x y:(float *)y eventFlags:(NSEventModifierFlags*)eventFlags
 {
     float dx = 0;
     float dy = 0;
 
-#if MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_7
+    NSUserDefaults *ud = [NSUserDefaults standardUserDefaults];
+
     if ([event hasPreciseScrollingDeltas]) {
         const NSEventPhase phase = event.phase;
-        NSUserDefaults *ud = [NSUserDefaults standardUserDefaults];
 
         CGFloat eventScrollingDeltaX = event.scrollingDeltaX;
         CGFloat eventScrollingDeltaY = event.scrollingDeltaY;
@@ -366,12 +366,40 @@ - (void)scrollWheel:(NSEvent *)event
         scrollingDeltaY = 0;
         dx = [event scrollingDeltaX];
         dy = [event scrollingDeltaY];
+
+        if ([ud boolForKey:MMMouseWheelDisableAccelerationKey]) {
+            // Use scroll wheel as discrete steps as macOS acceleration often
+            // leads to unintuitive results.
+            NSInteger numLines = [ud integerForKey:MMMouseWheelNumLinesKey];
+            dx = dx == 0 ? 0 : (dx > 0 ? numLines : -numLines);
+            dy = dy == 0 ? 0 : (dy > 0 ? numLines : -numLines);
+        } else {
+            // Use the default OS acceleration, but we still want to round up
+            // the delta to at least 1 (configurable) as otherwise it's
+            // frustrating to use as MacVim fails to scroll even one line.
+            NSInteger minScrollLines = [ud integerForKey:MMMouseWheelMinLinesKey];
+            dx = dx == 0 ? 0 : (fabs(dx) > minScrollLines ? dx : (dx > 0 ? minScrollLines : -minScrollLines));
+            dy = dy == 0 ? 0 : (fabs(dy) > minScrollLines ? dy : (dy > 0 ? minScrollLines : -minScrollLines));
+        }
+
+        if ((*eventFlags & NSEventModifierFlagShift) && dx != 0 && dy == 0) {
+            // A shift-scroll in macOS converts a normal Y to X-axis scroll.
+            // There is no proper API to query this so this is just done by
+            // heuristics. We need to remove the shift flag, or Vim would see
+            // this as a <S-ScrollWheelRight> which is not what we want.
+            *eventFlags = *eventFlags & (~NSEventModifierFlagShift);
+        }
     }
-#else
-    dx = [event deltaX];
-    dy = [event deltaY];
-#endif
 
+    *x = dx;
+    *y = dy;
+}
+
+- (void)scrollWheel:(NSEvent *)event
+{
+    NSEventModifierFlags eventFlags = event.modifierFlags;
+    float dx = 0, dy = 0;
+    [self calcScrollWheelDeltas:event x:&dx y:&dy eventFlags:&eventFlags];
     if (dx == 0 && dy == 0)
         return;
 
@@ -386,7 +414,7 @@ - (void)scrollWheel:(NSEvent *)event
     int row, col;
     NSPoint pt = [textView convertPoint:[event locationInWindow] fromView:nil];
     if ([textView convertPoint:pt toRow:&row column:&col]) {
-        unsigned flags = (unsigned)[event modifierFlags];
+        unsigned flags = (unsigned)eventFlags;
         NSMutableData *data = [NSMutableData data];
 
         [data appendBytes:&row length:sizeof(int)];

src/MacVim/Miscellaneous.h

@@ -61,6 +61,9 @@ extern NSString *MMUseInlineImKey;
 extern NSString *MMSuppressTerminationAlertKey;
 extern NSString *MMNativeFullScreenKey;
 extern NSString *MMUseMouseTimeKey;
+extern NSString *MMMouseWheelDisableAccelerationKey;    ///< Disable native macOS mouse scroll wheel acceleration
+extern NSString *MMMouseWheelMinLinesKey;   ///< Minimum scroll delta for mouse scroll wheel, only when acceleration is on
+extern NSString *MMMouseWheelNumLinesKey;   ///< Number of lines to scroll using mouse scroll wheel, only when acceleration is off
 extern NSString *MMFullScreenFadeTimeKey;
 extern NSString *MMNonNativeFullScreenShowMenuKey;
 extern NSString *MMNonNativeFullScreenSafeAreaBehaviorKey;
@@ -69,7 +72,7 @@ extern NSString *MMCmdLineAlignBottomKey;
 extern NSString *MMRendererClipToRowKey;
 extern NSString *MMAllowForceClickLookUpKey;
 extern NSString *MMUpdaterPrereleaseChannelKey;
-extern NSString *MMLastUsedBundleVersionKey;    // The last used version of MacVim before this launch
+extern NSString *MMLastUsedBundleVersionKey;    ///< The last used version of MacVim before this launch
 extern NSString *MMShowWhatsNewOnStartupKey;
 extern NSString *MMScrollOneDirectionOnlyKey;
 

src/MacVim/Miscellaneous.m

@@ -57,6 +57,9 @@
 NSString *MMSuppressTerminationAlertKey   = @"MMSuppressTerminationAlert";
 NSString *MMNativeFullScreenKey           = @"MMNativeFullScreen";
 NSString *MMUseMouseTimeKey               = @"MMUseMouseTime";
+NSString *MMMouseWheelDisableAccelerationKey    = @"MMMouseWheelDisbleAcceleration";
+NSString *MMMouseWheelMinLinesKey         = @"MMMouseWheelMinLines";
+NSString *MMMouseWheelNumLinesKey         = @"MMMouseWheelNumLines";
 NSString *MMFullScreenFadeTimeKey         = @"MMFullScreenFadeTime";
 NSString *MMNonNativeFullScreenShowMenuKey          = @"MMNonNativeFullScreenShowMenu";
 NSString *MMNonNativeFullScreenSafeAreaBehaviorKey  = @"MMNonNativeFullScreenSafeAreaBehavior";