Fri May 5 11:02:56 PDT 2006 Duncan Coutts <duncan@...>
* Document the Matrix representation
hunk ./cairo/Graphics/Rendering/Cairo/Matrix.chs 31
+  Representation of a 2D affine transformation as a matrix.
+
+ The 'Matrix' type actually represents as 3x3 matrix but with some elements
+ are constant and so are not included. Specifically if we assume that our
+ coordinates are row vectors then correspondence is:
+
+ > Matrix xx yx xy yy x0 y0
+ > ==
+ > / xx yx 0 \
+ >  xy yy 0 
+ > \ x0 y0 1 /
+
+ and the matrix operates on @(x,y)@ coordinates:
+
+ > (x y 1) / xx yx 0 \ = (x' y' 1)
+ >  xy yy 0  where x' = xx * x + xy * y + x0
+ > \ x0 y0 1 / y' = yx * x + yy * y + y0
+
