cocoa: Added hint to treat MacBook trackpads as touch devices, not mice.

Fixes #5511.

include/SDL_hints.h

@@ -2207,6 +2207,28 @@ extern "C" {
 #define SDL_HINT_KMSDRM_DEVICE_INDEX "SDL_KMSDRM_DEVICE_INDEX"
 
 
+/**
+ *  \brief  A variable that treats trackpads as touch devices.
+ *
+ *  On macOS (and possibly other platforms in the future), SDL will report
+ *  touches on a trackpad as mouse input, which is generally what users
+ *  expect from this device; however, these are often actually full
+ *  multitouch-capable touch devices, so it might be preferable to some apps
+ *  to treat them as such.
+ *
+ *  Setting this hint to true will make the trackpad input report as a
+ *  multitouch device instead of a mouse. The default is false.
+ *
+ *  Note that most platforms don't support this hint. As of 2.24.0, it
+ *  only supports MacBooks' trackpads on macOS. Others may follow later.
+ *
+ *  This hint is checked during SDL_Init and can not be changed after.
+ *
+ *  This hint is available since SDL 2.24.0.
+ */
+#define SDL_HINT_TRACKPAD_IS_TOUCH_ONLY "SDL_TRACKPAD_IS_TOUCH_ONLY"
+
+
 /**
  *  \brief  An enumeration of hint priorities
  */

src/video/cocoa/SDL_cocoavideo.h

@@ -99,6 +99,7 @@ DECLARE_ALERT_STYLE(Critical);
 
 @interface SDL_VideoData : NSObject
     @property (nonatomic) int allow_spaces;
+    @property (nonatomic) int trackpad_is_touch_only;
     @property (nonatomic) unsigned int modifierFlags;
     @property (nonatomic) void *key_layout;
     @property (nonatomic) SDLTranslatorResponder *fieldEdit;

src/video/cocoa/SDL_cocoavideo.m

@@ -197,6 +197,7 @@ Cocoa_VideoInit(_THIS)
     }
 
     data.allow_spaces = SDL_GetHintBoolean(SDL_HINT_VIDEO_MAC_FULLSCREEN_SPACES, SDL_TRUE);
+    data.trackpad_is_touch_only = SDL_GetHintBoolean(SDL_HINT_TRACKPAD_IS_TOUCH_ONLY, SDL_FALSE);
 
     data.swaplock = SDL_CreateMutex();
     if (!data.swaplock) {

src/video/cocoa/SDL_cocoawindow.h

@@ -56,6 +56,7 @@ typedef enum
     BOOL isDragAreaRunning;
 }
 
+-(BOOL) isTouchFromTrackpad:(NSEvent *)theEvent;
 -(void) listen:(SDL_WindowData *) data;
 -(void) pauseVisibleObservation;
 -(void) resumeVisibleObservation;

src/video/cocoa/SDL_cocoawindow.m

@@ -1359,26 +1359,39 @@ Cocoa_SendMouseButtonClicks(SDL_Mouse * mouse, NSEvent *theEvent, SDL_Window * w
     Cocoa_HandleMouseWheel(_data.window, theEvent);
 }
 
+
+- (BOOL)isTouchFromTrackpad:(NSEvent *)theEvent
+{
+    SDL_Window *window = _data.window;
+    SDL_VideoData *videodata = ((__bridge SDL_WindowData *) window->driverdata).videodata;
+
+    /* if this a MacBook trackpad, we'll make input look like a synthesized
+       event. This is backwards from reality, but better matches user
+       expectations. You can make it look like a generic touch device instead
+       with the SDL_HINT_TRACKPAD_IS_TOUCH_ONLY hint. */
+    BOOL istrackpad = NO;
+    if (!videodata.trackpad_is_touch_only) {
+        @try {
+            istrackpad = ([theEvent subtype] == NSEventSubtypeMouseEvent);
+        }
+        @catch (NSException *e) {
+            /* if NSEvent type doesn't have subtype, such as NSEventTypeBeginGesture on
+             * macOS 10.5 to 10.10, then NSInternalInconsistencyException is thrown.
+             * This still prints a message to terminal so catching it's not an ideal solution.
+             *
+             * *** Assertion failure in -[NSEvent subtype]
+             */
+        }
+    }
+    return istrackpad;
+}
+
 - (void)touchesBeganWithEvent:(NSEvent *) theEvent
 {
     NSSet *touches;
     SDL_TouchID touchID;
     int existingTouchCount;
-
-    /* probably a MacBook trackpad; make this look like a synthesized event.
-       This is backwards from reality, but better matches user expectations. */
-    BOOL istrackpad = NO;
-    @try {
-        istrackpad = ([theEvent subtype] == NSEventSubtypeMouseEvent);
-    }
-    @catch (NSException *e) {
-        /* if NSEvent type doesn't have subtype, such as NSEventTypeBeginGesture on
-         * macOS 10.5 to 10.10, then NSInternalInconsistencyException is thrown.
-         * This still prints a message to terminal so catching it's not an ideal solution.
-         *
-         * *** Assertion failure in -[NSEvent subtype]
-         */
-    }
+    const BOOL istrackpad = [self isTouchFromTrackpad:theEvent];
 
     touches = [theEvent touchesMatchingPhase:NSTouchPhaseAny inView:nil];
     touchID = istrackpad ? SDL_MOUSE_TOUCHID : (SDL_TouchID)(intptr_t)[[touches anyObject] device];
@@ -1426,24 +1439,10 @@ Cocoa_SendMouseButtonClicks(SDL_Mouse * mouse, NSEvent *theEvent, SDL_Window * w
 - (void)handleTouches:(NSTouchPhase) phase withEvent:(NSEvent *) theEvent
 {
     NSSet *touches = [theEvent touchesMatchingPhase:phase inView:nil];
+    const BOOL istrackpad = [self isTouchFromTrackpad:theEvent];
     SDL_FingerID fingerId;
     float x, y;
 
-    /* probably a MacBook trackpad; make this look like a synthesized event.
-       This is backwards from reality, but better matches user expectations. */
-    BOOL istrackpad = NO;
-    @try {
-        istrackpad = ([theEvent subtype] == NSEventSubtypeMouseEvent);
-    }
-    @catch (NSException *e) {
-        /* if NSEvent type doesn't have subtype, such as NSEventTypeBeginGesture on
-         * macOS 10.5 to 10.10, then NSInternalInconsistencyException is thrown.
-         * This still prints a message to terminal so catching it's not an ideal solution.
-         *
-         * *** Assertion failure in -[NSEvent subtype]
-         */
-    }
-
     for (NSTouch *touch in touches) {
         const SDL_TouchID touchId = istrackpad ? SDL_MOUSE_TOUCHID : (SDL_TouchID)(intptr_t)[touch device];
         SDL_TouchDeviceType devtype = SDL_TOUCH_DEVICE_INDIRECT_ABSOLUTE;