1 files changed, 53 insertions, 27 deletions

diff --git a/src/window.cpp b/src/window.cpp
index 2f4a5eb59..38b963bbd 100644
--- a/src/window.cpp
+++ b/src/window.cpp
@@ -1468,6 +1468,56 @@ void ResizeWindow(Window *w, int delta_x, int delta_y)
 	w->SetDirty();
 }
 
+/** The minimum number of pixels of the title bar must be visible in both the X or Y direction */
+static const int MIN_VISIBLE_TITLE_BAR = 13;
+
+/** Direction for moving the window. */
+enum PreventHideDirection {
+	PHD_UP,   ///< Above v is a safe position.
+	PHD_DOWN, ///< Below v is a safe position.
+};
+
+/**
+ * Do not allow hiding of the rectangle with base coordinates \a nx and \a ny behind window \a v.
+ * If needed, move the window base coordinates to keep it visible.
+ * @param nx   Base horizontal coordinate of the rectangle.
+ * @param ny   Base vertical coordinate of the rectangle.
+ * @param rect Rectangle that must stay visible for #MIN_VISIBLE_TITLE_BAR pixels (horizontally, vertically, or both)
+ * @param v    Window lying in front of the rectangle.
+ * @param px   Previous horizontal base coordinate.
+ * @param dir  If no room horizontally, move the rectangle to the indicated position.
+ */
+void PreventHiding(int *nx, int *ny, const Rect &rect, const Window *v, int px, PreventHideDirection dir)
+{
+	if (v == NULL) return;
+
+	int v_bottom = v->top + v->height;
+	int v_right = v->left + v->width;
+	int safe_y = (dir == PHD_UP) ? (v->top - MIN_VISIBLE_TITLE_BAR - rect.top) : (v_bottom + MIN_VISIBLE_TITLE_BAR - rect.bottom); // Compute safe vertical position.
+
+	if (*ny + rect.top <= v->top - MIN_VISIBLE_TITLE_BAR) return; // Above v is enough space
+	if (*ny + rect.bottom >= v_bottom + MIN_VISIBLE_TITLE_BAR) return; // Below v is enough space
+
+	/* Vertically, the rectangle is hidden behind v. */
+	if (*nx + rect.left + MIN_VISIBLE_TITLE_BAR < v->left) { // At left of v.
+		if (v->left < MIN_VISIBLE_TITLE_BAR) *ny = safe_y; // But enough room, force it to a safe position.
+		return;
+	}
+	if (*nx + rect.right - MIN_VISIBLE_TITLE_BAR > v_right) { // At right of v.
+		if (v_right > _screen.width - MIN_VISIBLE_TITLE_BAR) *ny = safe_y; // Not enough room, force it to a safe position.
+		return;
+	}
+
+	/* Horizontally also hidden, force movement to a safe area. */
+	if (px + rect.left < v->left && v->left >= MIN_VISIBLE_TITLE_BAR) { // Coming from the left, and enough room there.
+		*nx = v->left - MIN_VISIBLE_TITLE_BAR - rect.left;
+	} else if (px + rect.right > v_right && v_right <= _screen.width - MIN_VISIBLE_TITLE_BAR) { // Coming from the right, and enough room there.
+		*nx = v_right + MIN_VISIBLE_TITLE_BAR - rect.right;
+	} else {
+		*ny = safe_y;
+	}
+}
+
 static bool _dragging_window; ///< A window is being dragged or resized.
 
 static bool HandleWindowDragging()
@@ -1587,37 +1637,13 @@ static bool HandleWindowDragging()
 				caption_rect.bottom = caption->pos_y + caption->current_y;
 			}
 
-			/* The minimum number of pixels of the title bar must be visible
-			 * in both the X or Y direction */
-			static const int MIN_VISIBLE_TITLE_BAR = 13;
-
 			/* Make sure the window doesn't leave the screen */
 			nx = Clamp(nx, MIN_VISIBLE_TITLE_BAR - caption_rect.right, _screen.width - MIN_VISIBLE_TITLE_BAR - caption_rect.left);
 			ny = Clamp(ny, 0, _screen.height - MIN_VISIBLE_TITLE_BAR);
 
-			/* Make sure the title bar isn't hidden by behind the main tool bar */
-			Window *v = FindWindowById(WC_MAIN_TOOLBAR, 0);
-			if (v != NULL) {
-				int v_bottom = v->top + v->height;
-				int v_right = v->left + v->width;
-				if (ny + caption_rect.top >= v->top && ny + caption_rect.top < v_bottom) {
-					if ((v->left < MIN_VISIBLE_TITLE_BAR && nx + caption_rect.left < v->left) ||
-							(v_right > _screen.width - MIN_VISIBLE_TITLE_BAR && nx + caption_rect.right > v_right)) {
-						ny = v_bottom;
-					} else {
-						if (nx + caption_rect.left > v->left - MIN_VISIBLE_TITLE_BAR &&
-								nx + caption_rect.right < v_right + MIN_VISIBLE_TITLE_BAR) {
-							if (w->top >= v_bottom) {
-								ny = v_bottom;
-							} else if (w->left < nx) {
-								nx = v->left - MIN_VISIBLE_TITLE_BAR - caption_rect.left;
-							} else {
-								nx = v_right + MIN_VISIBLE_TITLE_BAR - caption_rect.right;
-							}
-						}
-					}
-				}
-			}
+			/* Make sure the title bar isn't hidden behind the main tool bar or the status bar. */
+			PreventHiding(&nx, &ny, caption_rect, FindWindowById(WC_MAIN_TOOLBAR, 0), w->left, PHD_DOWN);
+			PreventHiding(&nx, &ny, caption_rect, FindWindowById(WC_STATUS_BAR,   0), w->left, PHD_UP);
 
 			if (w->viewport != NULL) {
 				w->viewport->left += nx - w->left;