[cairo] 1.6: a8-mask: Making non-aligned strides illegal
behdad at behdad.org
Sun Jan 27 21:51:13 PST 2008
On Mon, 2008-01-28 at 00:35 -0500, Carl Worth wrote:
> On Thu, 24 Jan 2008 12:43:35 -0800, Carl Worth wrote:
> > • Fix a8mask failure cworth
> In talking with Keith, Eric, and Søren I've become convinced that
> instead of "supporting" rendering to/from an A8 mask with a
> non-multiple-of-4 stride value, we really do want to just document
> this as illegal.
> Forcing this kind of alignment will allow for many more optimization
> The inkscape folks had run into this problem and I had said we'd have
> a fix in 1.6. Instead, I'd like to volunteer to help fix the inkscape
> code to allocate buffers with a properly aligned stride. If some kind
> inkscape developer were willing to help me with this soon, that would
> be great.
> In order to make it easier to know what a "legal" stride is, (and to
> allow us to require more stringent alignment constraints in the
> future), I'm proposing the following new API:
> cairo_image_surface_stride_for_width (cairo_format_t format,
> int width);
I marginally prefer cairo_format_stride_for_width() as a name.
> And also documenting cairo_image_surface_create_for_data that the
> stride value passed to it should always come from calling the function
Humm, not sure how limiting that would be. Do you mean it should be the
stride_for_width() of the actual image width, 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.
Also while at this, how does this work for:
- 64-bit machines? Is the requirement still just 32? Guess yes.
- Machines that do not allow unaligned access. Do we also require
that data be aligned properly?
> More details, (and more thorough documentation), in the patches below.
> I'll push unless there are complaints.
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Temporary Safety, deserve neither Liberty nor Safety."
-- Benjamin Franklin, 1759
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