+/*
+ * Calculate which tiles need to be redrawn after resizing. This is the
+ * tiles which (at the new size) are fully contained in the previous area.
+ *
+ * When shrinking, this is all tiles, but when enlarging, the generated
+ * expose events will trigger drawing of the new area.
+ */
+static uint_fast32_t resize_helper(Widget w, Dimension *oldsz, int gridsz)
+{
+ Dimension new_w, new_h, common_w, common_h;
+
+ if (!XtIsRealized(w))
+ return 0;
+
+ XtVaGetValues(w, XmNwidth, &new_w, XmNheight, &new_h, (char *)NULL);
+ common_w = MIN(new_w, oldsz[0]);
+ common_h = MIN(new_h, oldsz[1]);
+ oldsz[0] = new_w;
+ oldsz[1] = new_h;
+ new_w /= gridsz;
+ new_h /= gridsz;
+
+ /* Round down to multiple of tile dimensions */
+ common_w = common_w / new_w * new_w;
+ common_h = common_h / new_h * new_h;
+
+ if (new_w > 0 && new_h > 0)
+ return expose_mask(0, 0, common_w, common_h, new_w, new_h);
+ return 0;
+}
+
+static void game_resize(Widget w, void *data, void *cb_data)
+{
+ struct app_state *state = data;
+ uint_fast32_t mask;
+
+ mask = resize_helper(w, state->game_sz, 5);
+ if (mask)
+ x11_redraw_game(data, mask);
+}
+
+static void goal_resize(Widget w, void *data, void *cb_data)
+{
+ struct app_state *state = data;
+ uint_fast32_t mask;
+
+ mask = resize_helper(w, state->goal_sz, 3);
+ if (mask)
+ x11_redraw_goal(data, mask);
+}
+