Function InputScrollViewport

src/openrct2-ui/input/MouseInput.cpp:1624–1689

    }

    void InputScrollViewport(const ScreenCoordsXY& scrollScreenCoords)
    {
        WindowBase* mainWindow = WindowGetMain();
        if (mainWindow == nullptr)
            return;

        Viewport* viewport = mainWindow->viewport;
        if (viewport == nullptr)
            return;

        const int32_t speed = Config::Get().general.edgeScrollingSpeed;

        int32_t multiplier = viewport->zoom.ApplyTo(speed);
        int32_t dx = scrollScreenCoords.x * multiplier;
        int32_t dy = scrollScreenCoords.y * multiplier;

        if (scrollScreenCoords.x != 0)
        {
            // Speed up scrolling horizontally when at the edge of the map
            // so that the speed is consistent with vertical edge scrolling.
            int32_t x = mainWindow->savedViewPos.x + viewport->ViewWidth() / 2 + dx;
            int32_t y = mainWindow->savedViewPos.y + viewport->ViewHeight() / 2;
            int32_t y_dy = mainWindow->savedViewPos.y + viewport->ViewHeight() / 2 + dy;

            auto mapCoord = ViewportPosToMapPos({ x, y }, 0, viewport->rotation);
            auto mapCoord_dy = ViewportPosToMapPos({ x, y_dy }, 0, viewport->rotation);

            // Check if we're crossing the boundary
            // Clamp to the map minimum value
            int32_t at_map_edge = 0;
            int32_t at_map_edge_dy = 0;
            if (mapCoord.x < kMapMinimumXY || mapCoord.y < kMapMinimumXY)
            {
                at_map_edge = 1;
            }
            if (mapCoord_dy.x < kMapMinimumXY || mapCoord_dy.y < kMapMinimumXY)
            {
                at_map_edge_dy = 1;
            }

            // Clamp to the map maximum value (scenario specific)
            auto mapSizeMinus2 = GetMapSizeMinus2();
            if (mapCoord.x > mapSizeMinus2.x || mapCoord.y > mapSizeMinus2.y)
            {
                at_map_edge = 1;
            }
            if (mapCoord_dy.x > mapSizeMinus2.x || mapCoord_dy.y > mapSizeMinus2.y)
            {
                at_map_edge_dy = 1;
            }

            // If we crossed the boundary, multiply the distance by 2
            if (at_map_edge && at_map_edge_dy)
            {
                dx *= 2;
            }

            mainWindow->savedViewPos.x += dx;