Add drag by touch

2 files changed, 71 insertions, 2 deletions

diff --git a/ImageView.py b/ImageView.py
index 6219cd7..8b81ca9 100644
--- a/ImageView.py
+++ b/ImageView.py
@@ -70,6 +70,7 @@ class ImageViewer(Gtk.DrawingArea):
         self._target_point = None
         self._anchor_point = None
 
+        self._in_dragtouch = False
         self._in_zoomtouch = False
         self._zoomtouch_scale = 1
 
@@ -160,10 +161,56 @@ class ImageViewer(Gtk.DrawingArea):
         self._do_set_zoom(1)
         self._center_if_small()
 
+    def start_dragtouch(self, coords):
+        self._in_dragtouch = True
+
+        prev_target_point = self._target_point
+
+        # Set target point to the relative coordinates of this view.
+        alloc = self.get_parent().get_allocation()
+        self._target_point = (coords[1], coords[2])
+
+        # Calculate the new anchor point.
+
+        prev_anchor_scaled = (self._anchor_point[0] * self._zoom,
+                              self._anchor_point[1] * self._zoom)
+
+        # This vector is the top left coordinate of the scaled image.
+        scaled_image_topleft = (prev_target_point[0] - prev_anchor_scaled[0],
+                                prev_target_point[1] - prev_anchor_scaled[1])
+
+        anchor_scaled = (self._target_point[0] - scaled_image_topleft[0],
+                         self._target_point[1] - scaled_image_topleft[1])
+
+        self._anchor_point = (int(anchor_scaled[0] * 1.0 / self._zoom),
+                              int(anchor_scaled[1] * 1.0 / self._zoom))
+
+        self.queue_draw()
+
+    def update_dragtouch(self, coords):
+        # Drag touch will be replaced by zoom touch if another finger
+        # is placed over the display.  When the user finishes zoom
+        # touch, it will probably remove one finger after the other,
+        # and this method will be called.  In that probable case, we
+        # need to start drag touch again.
+        if not self._in_dragtouch:
+            self.start_dragtouch(coords)
+            return
+
+        self._target_point = (coords[1], coords[2])
+        self.queue_draw()
+
+    def finish_dragtouch(self, coords):
+        self._in_dragtouch = False
+        self._center_if_small()
+
     def start_zoomtouch(self, center):
         self._in_zoomtouch = True
         self._zoomtouch_scale = 1
 
+        # Zoom touch replaces drag touch.
+        self._in_dragtouch = False
+
         prev_target_point = self._target_point
 
         # Set target point to the relative coordinates of this view.
@@ -266,7 +313,7 @@ class ImageViewer(Gtk.DrawingArea):
 
         ctx.set_source_surface(self._surface, 0, 0)
 
-        if self._in_zoomtouch:
+        if self._in_zoomtouch or self._in_dragtouch:
             ctx.get_source().set_filter(cairo.FILTER_NEAREST)
 
         ctx.paint()
diff --git a/ImageViewerActivity.py b/ImageViewerActivity.py
index 78e5679..a72642e 100644
--- a/ImageViewerActivity.py
+++ b/ImageViewerActivity.py
@@ -28,6 +28,7 @@ import time
 import os
 import math
 from gi.repository import Gtk
+from gi.repository import Gdk
 from gi.repository import GObject
 
 from sugar3.graphics.alert import NotifyAlert
@@ -117,14 +118,21 @@ class ImageViewerActivity(activity.Activity):
                                         Gtk.PolicyType.ALWAYS)
 
         # Don't use the default kinetic scrolling, let the view do the
-        # pinch to zoom logic.
+        # drag-by-touch and pinch-to-zoom logic.
         self.scrolled_window.set_kinetic_scrolling(False)
 
         self.view = ImageView.ImageViewer()
+
+        # Connect to the touch signal for performing drag-by-touch.
+        self.view.add_events(Gdk.EventMask.TOUCH_MASK)
+        self._touch_hid = self.view.connect('touch-event',
+                                            self.__touch_event_cb)
         self.scrolled_window.add_with_viewport(self.view)
         self.view.show()
 
         if GESTURES_AVAILABLE:
+            # Connect to the zoom signals for performing
+            # pinch-to-zoom.
             zoom_controller = SugarGestures.ZoomController()
             zoom_controller.attach(self,
                     SugarGestures.EventControllerFlags.NONE)
@@ -203,14 +211,28 @@ class ImageViewerActivity(activity.Activity):
                 # Wait for a successful join before trying to get the document
                 self.connect("joined", self._joined_cb)
 
+    def __touch_event_cb(self, widget, event):
+        coords = event.get_coords()
+        if event.type == Gdk.EventType.TOUCH_BEGIN:
+            self.view.start_dragtouch(coords)
+        elif event.type == Gdk.EventType.TOUCH_UPDATE:
+            self.view.update_dragtouch(coords)
+        elif event.type == Gdk.EventType.TOUCH_END:
+            self.view.finish_dragtouch(coords)
+
     def __zoomtouch_began_cb(self, controller):
         self.view.start_zoomtouch(controller.get_center())
 
+        # Don't listen to touch signals until pinch-to-zoom ends.
+        self.view.disconnect(self._touch_hid)
+
     def __zoomtouch_changed_cb(self, controller, scale):
         self.view.update_zoomtouch(controller.get_center(), scale)
 
     def __zoomtouch_ended_cb(self, controller):
         self.view.finish_zoomtouch()
+        self._touch_hid = self.view.connect('touch-event',
+                                            self.__touch_event_cb)
 
     def _add_toolbar_buttons(self, toolbar_box):
         activity_button = ActivityToolbarButton(self)