Re: [Gtk2hs-users] Cairo.Matrix documentation

[Duncan C. <dun...@wo...>]

On Thu, 2007-05-03 at 16:45 +0200, Malte Milatz wrote:
> I just want to comment on an oddity in the documentation for the Matrix
> type in Graphics.Rendering.Cairo.Matrix.

This all sounds sensible. If you send us a darcs patch with your changes
that'd be fantastic. You'd be looking at the haddock markup in
gtk2hs/cairo/Graphics/Rendering/Cairo/Matrix.chs

Duncan

>  Currently it states:
> 
> | data Matrix
> | 
> | Representation of a 2-D affine transformation as a matrix.
> | 
> | The Matrix type actually represents as 3x3 matrix but with some
> | elements are constant and so are not included. 
> 
> I think it's a little odd to interpret the Matrix datatype as a 3x3
> matrix, only to justify that it includes a translation vector. I would
> have written something along the lines:
> 
>     data Matrix
> 
>     Representation of a 2-D affine transformation.
> 
>     The Matrix type represents a 2x2 transformation matrix along with a
>     translation vector.
> 
> The documentation then goes on:
> 
> | Specifically if we assume that our
> | coordinates are row vectors then correspondence is:
> 
> Aren't column vectors usually used in analytic geometry? I wouldn't have
> had to scratch my head several times if the explanation were e. g. as
> follows:
> 
>     (Matrix a1 a2 b1 b2 c1 c2) describes the transformation of a point
>     with coordinates x,y that is defined by 
>     
>         / x' \  =  / a1 b1 \  / x \  + / c1 \
>         \ y' /     \ a2 b2 /  \ y /    \ c2 /
> 
>     or
> 
>         x' =  a1 * x + b1 * y + c1
>         y' =  a2 * x + b2 * y + c2
> 
> 
> 
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