Re: [Openexr-devel] Invert lines during reading process ?

[Gernot Ziegler]

Hej Florian !

> in order to load an image "upside down" you'd have to set
> your frame buffer's yStride to a negative value, but since
> yStride is of type size_t, which is unsigned, you can't
> do that.
(Yepp, I tried that and bombed my OpenEXR loader ;) )

> However, there is a workaround: unsigned integer arithmetic
Thanks for the... ehem ... unconventional tip, I will try it out !

To the original restriction:
Maybe the data type for the offset can be changed to signed long or
similar ? I can imagine that this will be useful to other real-time
processing guys, too ... :-)

> is usually implemented such that results are computed modulo
> (1<<b), where b is the number of bits in an unsigned integer.
> If n is positive and of type size_t, you can effectively set
> yStride to -n like this:
>
>      yStride = (~(size_t(0)) - n + 1);
>
> If x is of type size_t, and x >= n, then computing x + yStride
> yields x - n.

Servus,
  Gernot

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