[cairo] Negative coordinates with recording surfaces

[Adrian Johnson]

Have you tried the latest snapshot (1.15.6)? 1.15.4 and later contains
fixes for recording surfaces with negative extents.

On 06/07/17 16:58, Antony Lee wrote:
> Hi all,
> 
> I have am a bit puzzled with how negative coordinates interact with
> recording surfaces.  Consider the following cairocffi example:
> 
>     from cairocffi import *
>     surf = RecordingSurface(CONTENT_COLOR_ALPHA, None)
>     ctx = Context(surf)
>     ctx.move_to(-5, -5)
>     ctx.line_to(5, 5)
>     ctx.set_line_width(.001)  # so that ink extents are not affected by
>     linewidth
>     ctx.stroke()
>     print(surf.ink_extents())
> 
> 
> This gives (-5.0, -5.0, 10.0, 10.0), so ink_extents has correctly
> reported that we have something going from (-5, -5) to (5, 5) on the
> unbounded surface.
> 
> But replace the surface constructor call by
> 
>     surf = RecordingSurface(CONTENT_COLOR_ALPHA, (-10, -10, 20, 20))
> 
> 
> which is a surface that is large enough to cover our line.  (After all,
> the documentation encourages us to specify the extents, for better
> performance.)
> Now the same program gives (5.0, 5.0, 5.0, 5.0).  By playing around with
> the numbers, I *guess* that the origin is relative to the lower left
> corner of the recording surface, and the width and height are up to 0, 0
> but not beyond?
> 
> Shouldn't I get instead either (-5.0, -5.0, 10.0, 10.0) (same as with an
> unbounded surface), or at least (5.0, 5.0, 10.0, 10.0) (if the returned
> extents are relative to the lower left corner of the surface)?
> 
> Thanks in advance,
> 
> Antony Lee
> 
>