Use gesture_pan on macOS

The macOS built-in trackpad reports as GDK_SOURCE_MOUSE (not GDK_SOURCE_TOUCHPAD).
The _scrolled routing condition required either GDK_SOURCE_TOUCHPAD or a device previously seen in a pinch event (_touchpad).
On macOS, neither condition held before a pinch had been seen, so two-finger scroll events fell through to dt_view_manager_scrolled (image navigation) instead of gesture_pan (panning). A #ifdef GDK_WINDOWING_QUARTZ branch now routes all non-ctrl smooth scrolls to gesture_pan on macOS.

Net result: On macOS, zoom via pinch works (was already working), and pan via two-finger swipe now works via gesture_pan. Combined pinch+pan simultaneously is not possible at the GDK level on macOS — NSEventTypeMagnify does not deliver the translational component; it must be done as sequential operations (zoom then pan).

Author: da-phil

src/gui/gtk.c

@@ -778,9 +778,19 @@ static gboolean _scrolled(GtkWidget *widget,
   const gboolean is_known_gesture_device = (device == _touchpad);
   const gboolean is_smooth = event->direction == GDK_SCROLL_SMOOTH && !event->is_stop;
 
-  if(!ctrl_held
-     && (is_touchpad_source || is_known_gesture_device)
-     && is_smooth)
+#ifdef GDK_WINDOWING_QUARTZ
+  // On macOS/Quartz, the built-in trackpad reports as GDK_SOURCE_MOUSE, not
+  // GDK_SOURCE_TOUCHPAD.  Route every non-ctrl smooth scroll to gesture_pan so
+  // that two-finger panning works in views like darkroom (both standalone and
+  // interleaved with a pinch-zoom gesture whose translational component macOS
+  // delivers as a separate scroll stream).
+  const gboolean route_as_pan = !ctrl_held && is_smooth;
+#else
+  const gboolean route_as_pan = !ctrl_held
+                                && (is_touchpad_source || is_known_gesture_device)
+                                && is_smooth;
+#endif
+  if(route_as_pan)
   {
     gdouble delta_x = 0.0, delta_y = 0.0;
     if(!dt_gui_get_scroll_deltas(event, &delta_x, &delta_y))
@@ -810,9 +820,9 @@ static gboolean _scrolled(GtkWidget *widget,
   {
     dt_print(DT_DEBUG_INPUT,
              "[touchpad] smooth scroll not routed as pan:"
-             " ctrl=%d touchpad_source=%d known_gesture_dev=%d"
+             " ctrl=%d touchpad_source=%d known_gesture_dev=%d route_as_pan=%d"
              " device='%s' source-type=%d",
-             ctrl_held, is_touchpad_source, is_known_gesture_device,
+             ctrl_held, is_touchpad_source, is_known_gesture_device, route_as_pan,
              device ? gdk_device_get_name(device) : "<none>",
              device ? (int)gdk_device_get_source(device) : -1);
   }

src/views/darkroom.c

@@ -4208,19 +4208,12 @@ gboolean gesture_pinch(dt_view_t *self,
   if(!dev) return FALSE;
   (void)state;
   static float pinch_begin_tscale = 0.0f;
-#ifdef GDK_WINDOWING_QUARTZ
-  static double pinch_prev_x = 0.0, pinch_prev_y = 0.0;
-#endif
 
   if(phase == GDK_TOUCHPAD_GESTURE_PHASE_BEGIN)
   {
     pinch_begin_tscale =
       dt_dev_get_zoom_scale(&dev->full, dev->full.zoom, 1 << dev->full.closeup, FALSE)
       * dev->full.ppd;
-#ifdef GDK_WINDOWING_QUARTZ
-    pinch_prev_x = x;
-    pinch_prev_y = y;
-#endif
     dt_print(DT_DEBUG_INPUT,
              "[darkroom pinch] begin x=%.1f y=%.1f scale=%.6f state=0x%x"
              " -> begin_tscale=%.6f ppd=%.2f",
@@ -4252,20 +4245,14 @@ gboolean gesture_pinch(dt_view_t *self,
     return FALSE;
   }
 
-#ifdef GDK_WINDOWING_QUARTZ
-  // On macOS (GDK Quartz), NSEventTypeMagnify does not populate deltaX/deltaY,
-  // so GDK fills pinch->dx and pinch->dy with 0. Infer translation from the
-  // movement of the gesture focal point (midpoint between the two fingers).
-  const double eff_dx = x - pinch_prev_x;
-  const double eff_dy = y - pinch_prev_y;
-#else
+  // On macOS (GDK Quartz), NSEventTypeMagnify never populates dx/dy and the
+  // gesture focal-point x/y is set once at phase=BEGIN and does not update
+  // during the gesture — so both approaches to infer translation are zero.
+  // Pan on macOS therefore arrives as a separate smooth-scroll stream which is
+  // routed to gesture_pan by _scrolled() in gtk.c.
+  // On other platforms (Wayland/X11), dx/dy carry the actual translational delta.
   const double eff_dx = dx;
   const double eff_dy = dy;
-#endif
-#ifdef GDK_WINDOWING_QUARTZ
-  pinch_prev_x = x;
-  pinch_prev_y = y;
-#endif
 
   if(eff_dx != 0.0 || eff_dy != 0.0)
   {