static final function DrawMapGridBorder(Canvas C)
{
    local float D, X;
    local int i;
    local float Step;
    local float HalfStepViewSpace;
    local string Symbol;
    local float XL, YL;

    const GRID_LINES = 9;

    // TODO: we have to draw this in two places, ideally we don't need to loop through
    // all of this twice and can do it in once pass

    // Draw horizontal grid lines!
    Step = 1.0 / GRID_LINES;
    D = Viewport.Max.X - Viewport.Min.X;
    i = Floor(Viewport.Min.X / Step);
    j = Ceil(Viewport.Max.X / Step);
    HalfStepViewSpace = (Step / D) / 2;

    // TODO: pick a font to use (something that isn't crap, preferably)
    C.Font = none;

    while (; i < j; ++i)
    {
        // Convert from viewport-space to view-space.
        X = ((i * Step) - Viewport.Min.X) / D;

        if (i > 0 && X < 0)
        {
            // TODO: draw grid line
            DrawLine(X);
        }

        X += HalfStepViewSpace;

        if (X < 1)
        {
            Symbol = Asc(Char("A") + i);

            C.TextSize(Symbol, XL, YL);

            DrawText(Symbol);
        }
    }
}

/**
minx = 0.4
0.111111111111111
*/

static final function bool ClipLineToViewport(out float X0, out float Y0, out float X1, out float Y1, Box Viewport)
{
    local float T0, T1, DX, DY, P, Q, U;
    local int i;

    T0 = 0;
    T1 = 1;
    DX = X1 - X0;
    DY = Y1 - Y0;

    for (i = 0; i < 4; ++i)
    {
        if (i == 0)
        {
            P = -DX;
            Q = -(Viewport.Min.X - X0);
        }
        else if (i == 1)
        {
            P = DX;
            Q = Viewport.Max.X - X0;
        }
        else if (i == 2)
        {
            P = -DY;
            Q = -(Viewport.Min.Y - Y0);
        }
        else
        {
            P = DY;
            Q = Viewport.Max.Y - Y0;
        }

        U = Q / P;

        if (P == 0)
        {
            if (Q < 0)
            {
                return false;
            }
        }
        else if (P < 0)
        {
            if (U > T1)
            {
                return false;
            }
            if (U > T0)
            {
                T0 = u;
            }
        }
        else
        {
            if (U < T0)
            {
                return false;
            }

            if (U < T1)
            {
                T1 = u;
            }
    }

    X0 = X0 + T0 * DX;
    Y0 = Y0 + T0 * DY;
    X1 = X0 + T1 * DX;
    Y1 = Y0 + T1 * DY;

    return true;
}