Miscellany

    [ 1   0       0 ]   [ a b 0 ]   [ 1  0    0 ]   [ a                   b                  0 ]
T = [ 0   1       0 ] * [ c d 0 ] * [ 0  1    0 ] = [ c                   d                  0 ]
    [ -x  -(h-y)  1 ]   [ 0 0 1 ]   [ x  h-y  1 ]   [ x(1-a) - c(h-y)    -bx + (h-y)(1-d)    1 ]