GDK W32: Improve AeroSnap - don't resize windows that fit

This is what AeroSnap does. If a window is being unsnapped on
a new monitor, check if the work area is large enough for the
window to fit in its normal size. If the window fits, just
reposition it so that the ratio of
left-window-edge-to-screen-edge / right-window-edge-to-screen-edge
remains the same, without scaling the window.

https://bugzilla.gnome.org/show_bug.cgi?id=763013

gdk/win32/gdkwindow-win32.c

@@ -180,6 +180,9 @@ gdk_window_impl_win32_finalize (GObject *object)
 
   g_clear_object (&window_impl->cursor);
 
+  g_clear_pointer (&window_impl->snap_stash, g_free);
+  g_clear_pointer (&window_impl->snap_stash_int, g_free);
+
   if (window_impl->hicon_big != NULL)
     {
       GDI_CALL (DestroyIcon, (window_impl->hicon_big));
@@ -2940,13 +2943,55 @@ unsnap (GdkWindow  *window,
 
   GDK_NOTE (MISC, g_print ("Monitor work area %d x %d @ %d : %d\n", rect.width, rect.height, rect.x, rect.y));
 
-  /* Calculate actual unsnapped window size based on its
-   * old relative size. Same for position.
-   */
-  rect.x += round (rect.width * impl->snap_stash->x);
-  rect.y += round (rect.height * impl->snap_stash->y);
-  rect.width = round (rect.width * impl->snap_stash->width);
-  rect.height = round (rect.height * impl->snap_stash->height);
+  if (rect.width >= impl->snap_stash_int->width &&
+      rect.height >= impl->snap_stash_int->height)
+    {
+      /* If the window fits into new work area without resizing it,
+       * place it into new work area without resizing it.
+       */
+      gdouble left, right, up, down, hratio, vratio;
+      gdouble hscale, vscale;
+      gdouble new_left, new_up;
+
+      left = impl->snap_stash->x;
+      right = 1.0 - (impl->snap_stash->x + impl->snap_stash->width);
+      up = impl->snap_stash->y;
+      down = 1.0 - (impl->snap_stash->y + impl->snap_stash->height);
+      hscale = 1.0;
+
+      if (right > 0.001)
+        {
+          hratio = left / right;
+          hscale = hratio / (1.0 + hratio);
+        }
+
+      new_left = (gdouble) (rect.width - impl->snap_stash_int->width) * hscale;
+
+      vscale = 1.0;
+
+      if (down > 0.001)
+        {
+          vratio = up / down;
+          vscale = vratio / (1.0 + vratio);
+        }
+
+      new_up = (gdouble) (rect.height - impl->snap_stash_int->height) * vscale;
+
+      rect.x = round (rect.x + new_left);
+      rect.y = round (rect.y + new_up);
+      rect.width = impl->snap_stash_int->width;
+      rect.height = impl->snap_stash_int->height;
+    }
+  else
+    {
+      /* Calculate actual unsnapped window size based on its
+       * old relative size. Same for position.
+       */
+      rect.x += round (rect.width * impl->snap_stash->x);
+      rect.y += round (rect.height * impl->snap_stash->y);
+      rect.width = round (rect.width * impl->snap_stash->width);
+      rect.height = round (rect.height * impl->snap_stash->height);
+    }
 
   GDK_NOTE (MISC, g_print ("Unsnapped window size %d x %d @ %d : %d\n", rect.width, rect.height, rect.x, rect.y));
 
@@ -2954,6 +2999,7 @@ unsnap (GdkWindow  *window,
                           rect.width, rect.height);
 
   g_clear_pointer (&impl->snap_stash, g_free);
+  g_clear_pointer (&impl->snap_stash_int, g_free);
 }
 
 static void
@@ -2989,6 +3035,9 @@ stash_window (GdkWindow          *window,
   if (impl->snap_stash == NULL)
     impl->snap_stash = g_new0 (GdkRectangleDouble, 1);
 
+  if (impl->snap_stash_int == NULL)
+    impl->snap_stash_int = g_new0 (GdkRectangle, 1);
+
   GDK_NOTE (MISC, g_print ("monitor work area  %ld x %ld @ %ld : %ld\n",
                            hmonitor_info.rcWork.right - hmonitor_info.rcWork.left,
                            hmonitor_info.rcWork.bottom - hmonitor_info.rcWork.top,
@@ -3015,6 +3064,11 @@ stash_window (GdkWindow          *window,
   impl->snap_stash->width = (gdouble) width / (gdouble) (hmonitor_info.rcWork.right - hmonitor_info.rcWork.left);
   impl->snap_stash->height = (gdouble) height / (gdouble) (hmonitor_info.rcWork.bottom - hmonitor_info.rcWork.top);
 
+  impl->snap_stash_int->x = x;
+  impl->snap_stash_int->y = y;
+  impl->snap_stash_int->width = width;
+  impl->snap_stash_int->height = height;
+
   GDK_NOTE (MISC, g_print ("Stashed window %d x %d @ %d : %d as %f x %f @ %f : %f\n",
                            width, height, x, y,
                            impl->snap_stash->width, impl->snap_stash->height, impl->snap_stash->x, impl->snap_stash->y));

gdk/win32/gdkwindow-win32.h

@@ -224,6 +224,9 @@ struct _GdkWindowImplWin32
    */
   GdkRectangleDouble *snap_stash;
 
+  /* Also remember the same position, but in absolute form. */
+  GdkRectangle *snap_stash_int;
+
   /* Decorations set by gdk_window_set_decorations() or NULL if unset */
   GdkWMDecoration* decorations;