Bug in randr/rrtransform.c : RRTrasnformCompute()

[Stirling Westrup]

On Thu, Nov 3, 2016 at 3:45 PM, Stirling Westrup <swestrup at gmail.com> wrote:

> I've noticed that the transformation matrices that this function builds
> for rotated screens is not quite correct.
>
> In particular, it consistently builds maps from 0 to width or height
> instead of from 0 to width-1 or height-1.
>
> This means that an inverted screen maps (0,0) to (width,height) instead of
> (width-1,height-1). This causes out-of-boundary errors when mapping screens.
>
>
OMG. I just worked out that this is a *DELIBERATE* error in order to
accommodate the half-open-interval method of describing rectangles. The
transforms as created work for half-open boundaries, but then fail to work
for mapping individual pixels. If the code were fixed to correctly handle
pixel coordinates, all of the boundary calculations in X would be off by
one...



-- 
Stirling Westrup
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