Re: GtkCanvas requirements?

[Behdad Esfahbod <behdad behdad org>]

On Mon, 2007-04-23 at 19:19 -0400, Damon Chaplin wrote:
> 
> But the cairo API already uses doubles, for coordinates and
> transformations. So if the canvas used fixed point numbers you'd be
> converting to doubles and then back again. With 32-bit fixed point
> numbers you also cut down the maximum possible size of the canvas,
> plus
> you lose the precision of doubles (which may be important for some
> data
> visualization apps). 

I completely agree here with Damon.  With fixed point api, bug reports
will come in very soon that "if I zoom in 1000x on a point and try to
move it, it jumps around...".  We've had similar reports when people
tried to port Inkscape to cairo, because cairo uses a 16.16 fixed point
internally.  When you are locked with fixed point, it would be really
hard to get out of it.  On the other hand, since cairo has double api
already and we don't see adding fixedpoint api any time soon, the canvas
can do a good job at avoiding floating-point arithmetic completely and
use cairo transformations for all the work.  And we have been optimizing
cairo as much as possible to make this usecase fast for example for
non-scale non-rotation matrices.  Doing affine transformations
completely in fixedpoint is very hard, and probably even impossible to
support extreme zoom factors with.

-- 
behdad
http://behdad.org/

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