[cairo] Cool stuff
behdad at behdad.org
Mon Aug 31 16:43:32 PDT 2009
Comments inline. Far far from exhaustive. Just can't go over it all in a day
or a week!
On 08/31/2009 05:32 AM, Chris Wilson wrote:
> A couple of the more superficial changes first:
> * The skia backend. This is an update of Vlad's backend to pass
> everything that we can to Skia to use natively. It requires a
> recent build of skia and '--enable-skia --with-skia=/path/to/skia/'
> passed to configure. Like the qt backend this allows us to sanity
> check our code-paths, and my impression was that it was quite
> favourable towards cairo -- though I did not spend any time ensuring
> I had built Skia correctly for my system.
So, I'm totally clueless... Can skia become an alternative to pixman for
cairo? Or it's totally a different thing? Same question about Qt.
> * The Tee surface. This is a simple surface that has been talked about
> for some time, but without any pressing need for its inclusion. The
> idea (which hopefully I've remembered correctly from Behdad's
> outline) is that the tee uses a single master surface for which any
> query on the surface is redirected and one or more slaves. All
> drawing operations are then sent to both the master and all the
> slaves. (This was made significantly easy by making the clip part of
> the explicit drawing operation.) Essentially this allows us to clone
> the output to multiple different surface - initially used only for
> logging/recording purposes.
Yes, it looks very close to what I expected. Since this is a small bit I
easily understand, lemme review it here:
cairo_public cairo_surface_t *
cairo_tee_surface_create (cairo_surface_t *master);
cairo_tee_surface_append (cairo_surface_t *surface,
_append somehow suggests an ordering. I'd prefer _add and _remove. _remove()
is useful: you may want to start/stop XML logging.
cairo_public cairo_surface_t *
cairo_tee_surface_index (cairo_surface_t *abstract_surface,
s/abstract_surface/tee_surface/ or s/abstract_surface/surface/?
Again, _index is not my favorite. But works. I assume 0 will be master always?
To the implementation. I personally prefer to see the tee not change the
semantics of master at all. With that, I see two issues:
- create_similar() creates a tee dup'ing all the surfaces. It should
simply create_similar(master) IMO. I simply don't see any use in a tee similar,
- acquire_source_image() and snapshot() may return one of the slaves
depending on type. I understand why this is being done. However, it may fail
very badly since the slaves and master may have had different initial content.
They are not exchangeable.
> * The XML surface. Again another very simple surface that was added
> solely to record the sequence of operations that constituted this
> surface. The distinguishing factor is that its output is both very
> simple and explicit (e.g. no resource references for patterns, a
> surface pattern is either represented as an image or by its complete
> sequence of operations). My purpose behind adding such a 'useless'
> output is so that I could simply capture the complete state and feed
> it into a hierarchical delta-debugger to perform state bisection.
> (The XML format is then convenient since there is large body of DOM
> parsers - though the style of output is very simple to convert into a
> CairoScript trace using a simple/fast SAX parser.)
Interesting. I'll give it a try later.
> So those are the insignificant changes off the top of my head
True. But 1) involve API, 2) I don't understand the rasterization changes
anyway, so I may as well focus on these :P.
> time and motivation I will keep working on the delta-debugger, which
> will give a clear use case for the XML/tee surfaces. The current wip is
> util/cairo-sphinx which at the moment will emit traces for every context
> (captured from a live application) that differ between clients (for
> which I use LD_PRELOAD to explicitly set the cairo version to use).
When you're mostly done with this, some documentation about all the different
testing, perfing, and debugging tools :).
> On to the good stuff!
No comment on those right now. My only feeling is that the number of
different representations, compositors, and fastpaths is approaching ∞.
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