[cairo] 1.6: a8-mask: Making non-aligned strides illegal
cworth at cworth.org
Sun Jan 27 22:48:03 PST 2008
On Mon, 28 Jan 2008 00:51:13 -0500, Behdad Esfahbod wrote:
> > int
> > cairo_image_surface_stride_for_width (cairo_format_t format,
> > int width);
> I marginally prefer cairo_format_stride_for_width() as a name.
Oh, I might like that. I came up with the first name before I realized
that a format was needed here.
> > And also documenting cairo_image_surface_create_for_data that the
> > stride value passed to it should always come from calling the function
> > above.
> Humm, not sure how limiting that would be. Do you mean it should be the
> stride_for_width() of the actual image width,
"stride_for_width() of the actual image width" is what I intended.
> or the stride for some
> (any) width? I mean, say I want to create a cairo surface for a
> subsurface of a larger buffer. The width passed to cairo may be way
> smaller than the width used for stride computation.
So you might have noticed that I dropped the suggestion in the
documentation for cairo_image_surface_create_for_data that playing
games with stride is a good way to generate sub-surfaces. More on that
> Also while at this, how does this work for:
> - 64-bit machines? Is the requirement still just 32? Guess yes.
Yes. The requirement comes from the fact that all of pixman is
currently in terms of uint32_t. But, yes, the existence of 64-bit
architectures is exactly why we want to be able to "upgrade" the
alignment constraints in the future. Hence the newly required function
> - Machines that do not allow unaligned access. Do we also require
> that data be aligned properly?
Right. And this is why the sub-surface thing is a problem.
I tried to address this in the new documentation for
cairo_image_surface_create_for_data by stealing language from
malloc. What I'm trying to say there is that the data pointer needs to
be properly aligned for the current platform. Take a look at the
wording I used and see if you can improve it at all.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Size: 189 bytes
Desc: not available
Url : http://lists.cairographics.org/archives/cairo/attachments/20080127/41d16659/attachment.pgp
More information about the cairo