Method UpdateSizeAndPosition

src/dropdown.cpp:170–215

* Update size and position of window to fit dropdown list into available space. */

	 * Update size and position of window to fit dropdown list into available space.
	 */
	void UpdateSizeAndPosition()
	{
		Rect button_rect = this->wi_rect.Translate(this->parent->left, this->parent->top);

		/* Get the dimensions required for the list. */
		Dimension list_dim = GetDropDownListDimension(this->list);

		/* Set up dimensions for the items widget. */
		Dimension widget_dim = list_dim;
		widget_dim.width += WidgetDimensions::scaled.dropdownlist.Horizontal();
		widget_dim.height += WidgetDimensions::scaled.dropdownlist.Vertical();

		/* Width should match at least the width of the parent widget. */
		widget_dim.width = std::max<uint>(widget_dim.width, button_rect.Width());

		/* Available height below (or above, if the dropdown is placed above the widget). */
		uint available_height_below = std::max(GetMainViewBottom() - button_rect.bottom - 1, 0);
		uint available_height_above = std::max(button_rect.top - 1 - GetMainViewTop(), 0);

		/* Is it better to place the dropdown above the widget? */
		if (widget_dim.height > available_height_below && available_height_above > available_height_below) {
			FitAvailableHeight(widget_dim, list_dim, available_height_above);
			this->position.y = button_rect.top - widget_dim.height;
		} else {
			FitAvailableHeight(widget_dim, list_dim, available_height_below);
			this->position.y = button_rect.bottom + 1;
		}

		if (_current_text_dir == TD_RTL) {
			/* In case the list is wider than the parent button, the list should be right aligned to the button and overflow to the left. */
			this->position.x = button_rect.right + 1 - (int)(widget_dim.width + (list_dim.height > widget_dim.height ? NWidgetScrollbar::GetVerticalDimension().width : 0));
		} else {
			this->position.x = button_rect.left;
		}

		this->items_dim = widget_dim;
		this->GetWidget<NWidgetStacked>(WID_DM_SHOW_SCROLL)->SetDisplayedPlane(list_dim.height > widget_dim.height ? 0 : SZSP_NONE);

		/* Capacity is the average number of items visible */
		this->vscroll->SetCapacity(widget_dim.height - WidgetDimensions::scaled.dropdownlist.Vertical());
		this->vscroll->SetStepSize(list_dim.height / this->list.size());
		this->vscroll->SetCount(list_dim.height);

		/* If the dropdown is positioned above the parent widget, start selection at the bottom. */
		if (this->position.y < button_rect.top && list_dim.height > widget_dim.height) this->vscroll->UpdatePosition(INT_MAX);
	}

	void UpdateWidgetSize(WidgetID widget, Dimension &size, [[maybe_unused]] const Dimension &padding, [[maybe_unused]] Dimension &fill, [[maybe_unused]] Dimension &resize) override
	{