/*
    Read

        http://z0b.kapsi.fi/snippets.php
    
    before using this code. Thank you.
*/

// 'baseX' and 'baseY' is the common end on both lines,
// x1/x2/y1/y2 are other endpoints
float angleBetweenLines(const float baseX, const float baseY,
                        const float x1, const float y1, const float x2, const float y2)
{
    float a1 = (atan2(y2 - baseY, x2 - baseX)) * 57.29578122f,
          a2 = (atan2(y1 - baseY, x1 - baseX)) * 57.29578122f;

    a1 = fmod(a1 + 180.0f, 360.0f);
    a2 = fmod(a2 + 180.0f, 360.0f);

    return fmod((360.0f - a2) + a1, 360.0f);
}