window-list: fix HiDPI scaling for preview thumbnails

Account for cairo device scale factor when scaling the captured pixbuf
to the thumbnail surface, so the entire window content is shown on HiDPI
displays.

Author: vkareh

applets/wncklet/window-list.c

@@ -283,8 +283,8 @@ preview_window_thumbnail (WnckWindow   *wnck_window,
 	}
 
 	*thumbnail_scale = scale = gdk_window_get_scale_factor (window);
-	width = gdk_window_get_width (window) * scale;
-	height = gdk_window_get_height (window) * scale;
+	width = gdk_window_get_width (window);
+	height = gdk_window_get_height (window);
 
 	/* Strip invisible resize borders using _NET_FRAME_EXTENTS */
 	if (frame != win)
@@ -304,10 +304,10 @@ preview_window_thumbnail (WnckWindow   *wnck_window,
 
 			if (XGetWindowAttributes (xdpy, win, &wa))
 			{
-				int vis_w = (wa.width  + ext[0] + ext[1]) * scale;
-				int vis_h = (wa.height + ext[2] + ext[3]) * scale;
-				int border_x = (wa.x - (int) ext[0]) * scale;
-				int border_y = (wa.y - (int) ext[2]) * scale;
+				int vis_w = (wa.width  + ext[0] + ext[1]) / scale;
+				int vis_h = (wa.height + ext[2] + ext[3]) / scale;
+				int border_x = (wa.x - (int) ext[0]) / scale;
+				int border_y = (wa.y - (int) ext[2]) / scale;
 
 				if (border_x > 0 && vis_w < width)
 				{
@@ -328,24 +328,24 @@ preview_window_thumbnail (WnckWindow   *wnck_window,
 	/* Scale to configured size while maintaining aspect ratio */
 	if (width > height)
 	{
-		int max_size = MIN (width, tasklist->thumbnail_size * scale);
+		int max_size = MIN (width, tasklist->thumbnail_size);
 		ratio = (double) max_size / (double) width;
-		*thumbnail_width = max_size;
-		*thumbnail_height = (int) ((double) height * ratio);
+		*thumbnail_width = max_size * scale;
+		*thumbnail_height = (int) ((double) height * ratio) * scale;
 	}
 	else
 	{
-		int max_size = MIN (height, tasklist->thumbnail_size * scale);
+		int max_size = MIN (height, tasklist->thumbnail_size);
 		ratio = (double) max_size / (double) height;
-		*thumbnail_height = max_size;
-		*thumbnail_width = (int) ((double) width * ratio);
+		*thumbnail_height = max_size * scale;
+		*thumbnail_width = (int) ((double) width * ratio) * scale;
 	}
 
 	gdk_x11_display_error_trap_push (gdk_window_get_display (window));
 
 	GdkPixbuf *pixbuf = gdk_pixbuf_get_from_window (window,
-	                                                src_x / scale, src_y / scale,
-	                                                width / scale, height / scale);
+	                                                src_x, src_y,
+	                                                width, height);
 
 	if (gdk_x11_display_error_trap_pop (gdk_window_get_display (window)) || pixbuf == NULL)
 	{
@@ -358,7 +358,9 @@ preview_window_thumbnail (WnckWindow   *wnck_window,
 	                                        *thumbnail_height);
 	cairo_surface_set_device_scale (thumbnail, scale, scale);
 	cr = cairo_create (thumbnail);
-	cairo_scale (cr, ratio, ratio);
+	cairo_scale (cr,
+	             (double) *thumbnail_width / scale / gdk_pixbuf_get_width (pixbuf),
+	             (double) *thumbnail_height / scale / gdk_pixbuf_get_height (pixbuf));
 	gdk_cairo_set_source_pixbuf (cr, pixbuf, 0, 0);
 	cairo_paint (cr);
 	cairo_destroy (cr);