source engine DrawCircle & DrawRoundedRect

void DrawCircle(int x0, int y0, int radius, Engine::Color color)
{
    int x = radius;
    int y = 0;
    int xChange = 1 - (radius << 1);
    int yChange = 0;
    int radiusError = 0;

    while (x >= y)
    {
        for (int i = x0 - x; i <= x0 + x; i++)
        {
            Engine::m_pRenderer->DrawRect ( i, y0 + y, 1, 1, color );
            Engine::m_pRenderer->DrawRect ( i, y0 - y, 1, 1, color );
        }
        for (int i = x0 - y; i <= x0 + y; i++)
        {
            Engine::m_pRenderer->DrawRect ( i, y0 + x, 1, 1, color );
            Engine::m_pRenderer->DrawRect ( i, y0 - x, 1, 1, color );
        }

        y++;
        radiusError += yChange;
        yChange += 2;
        if (((radiusError << 1) + xChange) > 0)
        {
            x--;
            radiusError += xChange;
            xChange += 2;
        }
    }
}

void DrawRoundedRect ( int x, int y, int w, int h, int smooth, Engine::Color color )
{
    Engine::m_pRenderer->DrawRect ( x + smooth, y, w - smooth * 2, h, color );
    Engine::m_pRenderer->DrawRect ( x, y + smooth, w, h - smooth * 2, color );

    DrawCircle ( x + smooth, y + smooth, smooth, color ); // left top
    DrawCircle ( x + w - smooth, y + smooth, smooth - 1, color ); // right top
    DrawCircle ( x + smooth, y + h - smooth, smooth - 1, color ); // left bottom
    DrawCircle ( x + w - smooth, y + h - smooth, smooth - 1, color ); // right bottom
}