Function ListBoxAt

Siv3D/src/Siv3D/SimpleGUI/SivSimpleGUI.cpp:1826–2051

		}

		bool ListBoxAt(ListBoxState& state, const Vec2& center, const double width, const double height, const bool enabled)
		{
			const Optional<size_t> oldState = state.selectedItemIndex;

			const Font& font = SimpleGUI::GetFont();
			const int32 maxLines = (static_cast<int32>(height) - (ListBoxFrameThickness * 2)) / font.height();
			const bool hasScrollBar = (maxLines < static_cast<int32>(state.items.size()));
			const RectF rect{ Arg::center(center), Max(width, 40.0), Max<double>(height, font.height() + (ListBoxFrameThickness * 2)) };
			const Vec2 pos = rect.pos;

			const int32 fontHeight = font.height();
			const int32 lines = Min(static_cast<int32>(state.items.size()), maxLines);
			const int32 itemWidth = static_cast<int32>(rect.w - (ListBoxFrameThickness * 2) - (hasScrollBar ? ScrollBarWidth : 0));

			if (state.items.isEmpty())
			{
				state.selectedItemIndex.reset();
			}
			else if (state.items.size() <= state.selectedItemIndex)
			{
				state.selectedItemIndex = (state.items.size() - 1);
			}

			// update
			{
				if (enabled)
				{
					for (int32 i = 0; i < lines; ++i)
					{
						const size_t itemIndex = (state.scroll + i);
						const RectF itemRect(pos.x + ListBoxFrameThickness, pos.y + ListBoxFrameThickness + (fontHeight * i), itemWidth, fontHeight);

						if (itemRect.leftClicked())
						{
							state.active = true;
							state.selectedItemIndex = itemIndex;
						}
					}
				}
				
				if ((not enabled) || (MouseL.down() && not rect.mouseOver()))
				{
					state.active = false;
				}

				if (state.active && state.selectedItemIndex)
				{
					if ((0 < *state.selectedItemIndex) &&
						(KeyUp.down() || ((SecondsF{ 0.33 } < KeyUp.pressedDuration()) && (SecondsF{ 0.06 } < state.upPressStopwatch))))
					{
						--(*state.selectedItemIndex);
						state.upPressStopwatch.restart();

						if (hasScrollBar  && (static_cast<int32>(*state.selectedItemIndex) < state.scroll))
						{
							state.scroll = Max(state.scroll - 1, 0);
						}
					}