From e01ee4acac69ba49fd89d933ded5fa3edfaceca7 Mon Sep 17 00:00:00 2001
From: Manuel Quiñones <manuq@laptop.org>
Date: Fri, 17 May 2013 01:13:53 +0000
Subject: Finally implement scrolling by trackpad

---
(limited to 'ImageView.py')

diff --git a/ImageView.py b/ImageView.py
index 6c00d4b..d7bee8f 100644
--- a/ImageView.py
+++ b/ImageView.py
@@ -60,6 +60,7 @@ def _rotate_surface(surface, direction):
 
     return new_surface
 
+
 class ImageViewer(Gtk.DrawingArea, Gtk.Scrollable):
     __gtype_name__ = 'ImageViewer'
 
@@ -102,9 +103,14 @@ class ImageViewer(Gtk.DrawingArea, Gtk.Scrollable):
         self.queue_draw()
 
     def do_get_property(self, prop):
+        # We don't use the getter but GTK wants it defined as we are
+        # implementing Gtk.Scrollable interface.
         pass
 
     def do_set_property(self, prop, value):
+        # The scrolled window will give us the adjustments.  Make a
+        # reference to them and also connect to their value-changed
+        # signal.
         if prop.name == 'hadjustment':
             if value is not None:
                 hadj = value
@@ -188,21 +194,35 @@ class ImageViewer(Gtk.DrawingArea, Gtk.Scrollable):
                                                   self._stop_scrolling)
 
     def __hadj_value_changed_cb(self, adj):
-        # move anchor and queue draw
         alloc = self.get_allocation()
+        scaled_width = self._surface.get_width() * self._zoom
+        anchor_scaled_x = self._anchor_point[0] * self._zoom
+        scaled_image_left = self._target_point[0] - anchor_scaled_x
+
+        max_left = scaled_width - alloc.width
+        max_value = 1.0 - adj.get_page_size()
+        new_left = -1 * max_left * adj.get_value() / max_value
 
-        dif = 10
-        self._anchor_point = (self._anchor_point[0] + dif,
+        delta_x = scaled_image_left - new_left
+        self._anchor_point = (self._anchor_point[0] + delta_x,
                               self._anchor_point[1])
 
         self._start_scrolling()
         self.queue_draw()
 
     def __vadj_value_changed_cb(self, adj):
+        alloc = self.get_allocation()
+        scaled_height = self._surface.get_height() * self._zoom
+        anchor_scaled_y = self._anchor_point[1] * self._zoom
+        scaled_image_top = self._target_point[1] - anchor_scaled_y
+
+        max_top = scaled_height - alloc.height
+        max_value = 1.0 - adj.get_page_size()
+        new_top = -1 * max_top * adj.get_value() / max_value
 
-        dif = 10
+        delta_y = scaled_image_top - new_top
         self._anchor_point = (self._anchor_point[0],
-                              self._anchor_point[1] + dif)
+                              self._anchor_point[1] + delta_y)
 
         self._start_scrolling()
         self.queue_draw()
--
cgit v0.9.1