void floodFillScanlineStack(Paint::Bitmap^ bm, int x, int y, System::Drawing::Color newColor, System::Drawing::Color oldColor)
{
    if (oldColor == newColor) return;

    int x1;
    bool spanAbove, spanBelow;

    std::vector<int> stackX, stackY;
    stackX.push_back(x);
    stackY.push_back(y);

    while (!stackX.empty())
    {
        x = stackX.back(); y = stackY.back();
        stackX.pop_back(); stackY.pop_back();

        x1 = x;
        while (x1 >= 0 && bm->GetPixel(x1, y) == oldColor) x1--;
        x1++;
        spanAbove = spanBelow = 0;
        while (x1 < bm->Width && bm->GetPixel(x1, y) == oldColor)
        {
            bm->SetPixel(x1, y, newColor);

            if (!spanAbove && y > 0 && bm->GetPixel(x1, y - 1) == oldColor)
            {
                stackX.push_back(x1);
                stackY.push_back(y - 1);

                spanAbove = 1;
            }
            else if (spanAbove && y > 0 && bm->GetPixel(x1, y - 1) != oldColor)
            {
                spanAbove = 0;
            }
            if (!spanBelow && y < bm->Height - 1 && bm->GetPixel(x1, y + 1) == oldColor)
            {
                stackX.push_back(x1);
                stackY.push_back(y + 1);

                spanBelow = 1;
            }
            else if (spanBelow && y < bm->Height - 1 && bm->GetPixel(x1, y + 1) != oldColor)
            {
                spanBelow = 0;
            }
            x1++;
        }
    }
}

void Paint::PaintForm::Fill(int x, int y, Color newClr, Color oldClr)
{
    floodFillScanlineStack(Img, x, y, newClr, oldClr);
}