user input: store mt positions separately

To report the correct position for the touch up event, we store the
last touched position.

Store the touch position separetely for each mt slot instead of keeping
a single position per input device.

src/user_input.c

@@ -27,7 +27,6 @@
 struct input_device_data {
     int64_t flutter_device_id_offset;
     struct keyboard_state *keyboard_state;
-    double x, y;
     int64_t buttons;
     uint64_t timestamp;
 
@@ -44,6 +43,12 @@ struct input_device_data {
      *
      */
     bool tip;
+
+    /**
+     * @brief The current touch positions for each multitouch slot.
+     *  
+     */
+    struct vec2f *positions;
 };
 
 struct user_input {
@@ -357,6 +362,7 @@ static void maybe_disable_mouse_cursor(struct user_input *input, uint64_t timest
 static int on_device_added(struct user_input *input, struct libinput_event *event, uint64_t timestamp) {
     struct input_device_data *data;
     struct libinput_device *device;
+    struct vec2f *positions;
     int64_t device_id;
 
     assert(input != NULL);
@@ -371,12 +377,11 @@ static int on_device_added(struct user_input *input, struct libinput_event *even
 
     data->flutter_device_id_offset = input->next_unused_flutter_device_id;
     data->keyboard_state = NULL;
-    data->x = 0.0;
-    data->y = 0.0;
     data->buttons = 0;
     data->timestamp = timestamp;
     data->has_emitted_pointer_events = false;
     data->tip = false;
+    data->positions = NULL;
 
     libinput_device_set_user_data(device, data);
 
@@ -389,14 +394,32 @@ static int on_device_added(struct user_input *input, struct libinput_event *even
         // reserve one id for the mouse pointer
         // input->next_unused_flutter_device_id++;
     }
+
     if (libinput_device_has_capability(device, LIBINPUT_DEVICE_CAP_TOUCH)) {
         // add all touch slots as individual touch devices to flutter
-        for (int i = 0; i < libinput_device_touch_get_touch_count(device); i++) {
+        int n_slots = libinput_device_touch_get_touch_count(device);
+        if (n_slots == -1) {
+            LOG_ERROR("Could not query input device multitouch slot count.\n");
+            goto fail_free_data;
+        } else if (n_slots == 0) {
+            LOG_ERROR("Input devive has unknown number of multitouch slots.\n");
+            goto fail_free_data;
+        }
+
+        for (int i = 0; i < n_slots; i++) {
             device_id = input->next_unused_flutter_device_id++;
 
             emit_pointer_events(input, &FLUTTER_POINTER_TOUCH_ADD_EVENT(timestamp, 0.0, 0.0, device_id), 1);
         }
+
+        positions = malloc(n_slots * sizeof(struct vec2f));
+        if (positions == NULL) {
+            goto fail_free_data;
+        }
+
+        data->positions = positions;
     }
+
     if (libinput_device_has_capability(device, LIBINPUT_DEVICE_CAP_KEYBOARD)) {
         // create a new keyboard state for this keyboard
         if (input->kbdcfg) {
@@ -406,6 +429,7 @@ static int on_device_added(struct user_input *input, struct libinput_event *even
             data->keyboard_state = NULL;
         }
     }
+
     if (libinput_device_has_capability(device, LIBINPUT_DEVICE_CAP_TABLET_TOOL)) {
         device_id = input->next_unused_flutter_device_id++;
 
@@ -414,6 +438,10 @@ static int on_device_added(struct user_input *input, struct libinput_event *even
     }
 
     return 0;
+
+    fail_free_data:
+    free(data);
+    return EINVAL;
 }
 
 static int on_device_removed(struct user_input *input, struct libinput_event *event, uint64_t timestamp, bool emit_flutter_events) {
@@ -465,6 +493,9 @@ static int on_device_removed(struct user_input *input, struct libinput_event *ev
     }
 
     if (data != NULL) {
+        if (data->positions != NULL) {
+            free(data->positions);
+        }
         free(data);
     }
 
@@ -687,9 +718,6 @@ static int on_mouse_motion_absolute_event(struct user_input *input, struct libin
         libinput_event_pointer_get_absolute_y_transformed(pointer_event, input->display_height)
     );
 
-    /// FIXME: Why do we store the coordinates here?
-    data->x = pos_display.x;
-    data->y = pos_display.y;
     data->timestamp = timestamp;
 
     // update the "global" cursor position
@@ -889,8 +917,7 @@ static int on_touch_down(struct user_input *input, struct libinput_event *event)
     emit_pointer_events(input, &FLUTTER_POINTER_TOUCH_DOWN_EVENT(timestamp, pos_view.x, pos_view.y, device_id), 1);
 
     // alter our device state
-    data->x = pos_view.x;
-    data->y = pos_view.y;
+    data->positions[slot] = pos_view;
     data->timestamp = timestamp;
 
     return 0;
@@ -919,7 +946,7 @@ static int on_touch_up(struct user_input *input, struct libinput_event *event) {
 
     device_id = data->flutter_device_id_offset + slot;
 
-    emit_pointer_events(input, &FLUTTER_POINTER_TOUCH_UP_EVENT(timestamp, data->x, data->y, device_id), 1);
+    emit_pointer_events(input, &FLUTTER_POINTER_TOUCH_UP_EVENT(timestamp, data->positions[slot].x, data->positions[slot].y, device_id), 1);
 
     return 0;
 }
@@ -961,8 +988,7 @@ static int on_touch_motion(struct user_input *input, struct libinput_event *even
     emit_pointer_events(input, &FLUTTER_POINTER_TOUCH_MOVE_EVENT(timestamp, pos_view.x, pos_view.y, device_id), 1);
 
     // alter our device state
-    data->x = pos_view.x;
-    data->y = pos_view.y;
+    data->positions[slot] = pos_view;
     data->timestamp = timestamp;
 
     return 0;