test_affine_map.c running 
x0=3.000000,y0=2.000000  to  a=0,b=0 
x1=8.000000,y1=5.000000  to  a=1,b=0 
x2=6.000000,y2=9.000000  to  a=0,b=1 

fabtoxy 0.000000,0.000000 -> 3.000000,2.000000 
fabtoxy 0.000000,0.333333 -> 4.000000,4.333333 
fabtoxy 0.000000,0.666667 -> 5.000000,6.666667 
fabtoxy 0.000000,1.000000 -> 6.000000,9.000000 
fabtoxy 0.333333,0.000000 -> 4.666667,3.000000 
fabtoxy 0.333333,0.333333 -> 5.666667,5.333333 
fabtoxy 0.333333,0.666667 -> 6.666667,7.666667 
fabtoxy 0.666667,0.000000 -> 6.333333,4.000000 
fabtoxy 0.666667,0.333333 -> 7.333333,6.333333 
fabtoxy 1.000000,0.000000 -> 8.000000,5.000000 

fxytoab 3.000000,2.000000 -> -0.000000,-0.000000 
fxytoab 8.000000,5.000000 -> 1.000000,-0.000000 
fxytoab 6.000000,9.000000 -> -0.000000,1.000000 
fxytoab 5.500000,3.500000 -> 0.500000,-0.000000 
fxytoab 7.000000,7.000000 -> 0.500000,0.500000 
fxytoab 4.500000,5.500000 -> -0.000000,0.500000 
fxytoab 5.666667,5.333333 -> 0.333333,0.333333