float getValueBilinearClamp( float x, float y ) const
{
    // Clamp negatives to zero (to get correct sub-pixel offset).
    x = max(0.f, x);
    y = max(0.f, y);

    // Separate floats into wholes (pixels) and fractions
    const int xi = (int)x;
    const int yi = (int)y;

    // Fraction
    const float xFract = (x - xi);
    const float yFract = (y - yi);

    // Clamp to max
    const int w = mapWidth - 1;
    const int h = mapHeight - 1;

    const int xi0 = min(xi, w);
    const int yi0 = min(yi, h);
    const int xi1 = min(xi + 1, w);
    const int yi1 = min(yi + 1, h);

    // Read pixels.
    const float s00 = getValue(xi0, yi0);
    const float s10 = getValue(xi1, yi0);
    const float s01 = getValue(xi0, yi1);
    const float s11 = getValue(xi1, yi1);

    // Bilinear filter
    const float bx0 = lerp(xFract, s00, s10);
    const float bx1 = lerp(xFract, s01, s11);
    return lerp(yFract, bx0, bx1);
}