Touchpad Mouse Conflation Problem

[fhoenig]

I've tried to get touch events from my Mac touchpad and by default no SDL_FINGER* nor SDL_MULTIGESTURE event are generated.

int td = SDL_GetNumTouchDevices(); // td is 1 here in my case
So I do have one touch device, which is correct.

Now I found that the only way to generate touch event from my touch device is to tell SDL that it is in fact a mouse.
SDL_SetHint(SDL_HINT_MOUSE_TOUCH_EVENTS, "1");

However this now also generates SDL_FINGER* events from the actual mouse I have connected, which isn't a touch device.

How can I tell SDL that I want the finger events only from the touch device?

[slouken]

The Mac touchpad is treated as a mouse, because that matches general user expectations.

Here's the relevant code in SDL_cocoawindow.m:

- (void)handleTouches:(NSTouchPhase) phase withEvent:(NSEvent *) theEvent
{
    NSSet *touches = [theEvent touchesMatchingPhase:phase inView:nil];

    /* 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);
    }

[slouken]

We could potentially add a hint to allow applications to change how this is handled. Adding @icculus for more discussion.

[icculus]

Yeah, this has been an ongoing thing...the hint is probably the right thing to do here. I'll fix that up for 2.0.24.

[icculus]

Just pasting this untested thing here until I can sit at the desk where the Mac Mini is.

(But feedback is welcome in the meantime!)

diff --git a/include/SDL_hints.h b/include/SDL_hints.h
index 368cb0a3c..9da512683 100644
--- a/include/SDL_hints.h
+++ b/include/SDL_hints.h
@@ -2175,6 +2175,24 @@ extern "C" {
 #define SDL_HINT_KMSDRM_DEVICE_INDEX "SDL_KMSDRM_DEVICE_INDEX"
 
 
+/**
+ *  \brief  A variable that treats MacBook trackpads as touch devices.
+ *
+ *  On macOS, SDL will report touches on the trackpad as mouse input, which
+ *  is generally what users expect from this device; however, these are
+ *  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.
+ *
+ *  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_MAC_TRACKPAD_IS_TOUCH_ONLY "SDL_MAC_TRACKPAD_IS_TOUCH_ONLY"
+
+
 /**
  *  \brief  An enumeration of hint priorities
  */
diff --git a/src/video/cocoa/SDL_cocoavideo.h b/src/video/cocoa/SDL_cocoavideo.h
index 4de8511a3..8f4a413e9 100644
--- a/src/video/cocoa/SDL_cocoavideo.h
+++ b/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;
diff --git a/src/video/cocoa/SDL_cocoavideo.m b/src/video/cocoa/SDL_cocoavideo.m
index 987fa2d4d..94c1b4020 100644
--- a/src/video/cocoa/SDL_cocoavideo.m
+++ b/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_MAC_TRACKPAD_IS_TOUCH_ONLY, SDL_FALSE);
 
     data.swaplock = SDL_CreateMutex();
     if (!data.swaplock) {
diff --git a/src/video/cocoa/SDL_cocoawindow.h b/src/video/cocoa/SDL_cocoawindow.h
index 9691fa3f1..ec25e1f57 100644
--- a/src/video/cocoa/SDL_cocoawindow.h
+++ b/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;
diff --git a/src/video/cocoa/SDL_cocoawindow.m b/src/video/cocoa/SDL_cocoawindow.m
index 1e47390be..83209b802 100644
--- a/src/video/cocoa/SDL_cocoawindow.m
+++ b/src/video/cocoa/SDL_cocoawindow.m
@@ -1364,26 +1364,38 @@ Cocoa_SendMouseButtonClicks(SDL_Mouse * mouse, NSEvent *theEvent, SDL_Window * w
     Cocoa_HandleMouseWheel(_data.window, theEvent);
 }
 
+
+- (BOOL)isTouchFromTrackpad:(NSEvent *)theEvent
+{
+    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_MAC_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];
@@ -1431,24 +1443,10 @@ 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;

[cgutman]

Let’s do a non-platform-specific hint because we’ll need the same option for Evdev trackpad support too.

[icculus]

My understanding is that this is a special case in our macOS handling...are you sure?

[cgutman]

Right now all evdev multi-touch trackpads are reporting touch events rather than mouse events. We'll probably want to change it to synthesize mouse events like macOS and provide an opt-out for apps that want the raw touch events back.

[icculus]

But for 2.24.0, you just want the word "MAC" out of the hint, so we can later apply it to evdev, right? If so, I'm fine with that.

[cgutman]

Yeah, just wanted to avoid painting ourselves into a corner and needing a second hint.