Hey Mike,
Thanks for your informative assessment of Canvas vs SVG. Indeed it
encapsulates much of the thinking and horse trading
done when we decided on Canvas as a delivery technology for mplh5canvas.
For us the plus points for Canvas came down to our perception of
better future browser support, and that most of the browsers seemed to
be putting
a large push into Canvas performance. Coupled with the use of
WebSockets, we felt an all HTML5 solution may be more universally
supported
in the long run. (although who can tell what the browser vendors are
actually thinking 
Yeah. I'll start implementing the "crystal ball" backend so we can answer that question 
Our initial testing showed that DOM manipulation was a surprising
bottleneck in SVG animations and that, particularly as the SVG object
count increased,
Canvas performance (time to raster) was better.
Interesting result. I wonder if browsers differ in that respect. I've been using Firefox 4 primarily, but testing with Chrome as well, and have been nothing but impressed with SVG performance -- but I'm only doing getElementById and then tweaking attributes, not actually changing tree morphology.
Also the rendering of
the imshow inline png's was a lot quicker than the SVG equivalent in
our initial testing.
Have you tried non-inline PNGs? The only need for inline PNGs is to have a self-contained SVG file. When one has a webapp server available that is no longer necessary. I suspect the encoding to/from base64 adds some overhead.
Obviously the vector strengths of SVG are highlighted with higher
output DPI, and this is certainly an area of interest.
True. Of course, given that we already have a static SVG backend that works, it should be simple enough to have a "Print" button that generates SVG only when printing (much like Google Docs generates a PDF when printing).
This mail is mostly to give others a bit of background about our
choice, I think it could easily have gone either way, and perhaps it
should.
Yes -- perhaps still an open question.
I should probably also add: I have sort of a bias toward a smart server/dumb client approach to continue to leverage the existing matplotlib code as much as possible -- which is kind of at odds with the ideal arrangement for best interactive performance, which would be to move a bunch of logic into Javascript. I don't have anything against plotting with Javascript -- there are some great packages out there -- but then it becomes a very different beast. I think your work has that assumption behind it as well, but speaking to some folks at Sage Days, it's not always implied when people start drafting a plan to do this.
Cheers,
Mike
···
On 06/13/2011 10:07 AM, Simon Ratcliffe wrote:
SKA South Africa
www.ska.ac.za
My (humble) assessment is that HTML 5 Canvas doesn't make much sense for
any of the use cases I could dream up, and that in fact SVG is a more
appropriate choice for interactive graphics. The browser support for
each technology is fairly equivalent at this point, with IE9 finally
getting on the SVG bandwagon. The main problem with Canvas (from the
point of view of matplotlib) is that it doesn't support persistence,
(without building such a layer on top in JavaScript), so if you want to
update the figure, you have to send the whole thing over the wire each
time. SVG, on the other hand, maintains a tree of objects that can be
tweaked at any time (and the performance in the current generation of
browsers is stunning). One could send all of the large data objects as
SVG from matplotlib to the browser and using XML ids to maintain
relationships between the client and the server. Then, do scale the
data (in many common cases), it is just a matter of updating the affiine
transform on that object, (as well as updating the ticks etc, but that's
peanuts), which requires very little bandwidth. I have some hackish
"proof of concept" code doing this kind of thing, but it's a long way
from there to something that truly works.
This all glosses over the path simplification stuff that matplotlib does
-- the assumption here is that the browser would have access to *all* of
the data, and there are probably practical limits on how big that data
can be.
I recently did a lot of cleanup to the SVG backend to pave the way for
having persistent objects etc. -- though there is no client/server code
at all in master at the moment. All of that is "to be written", perhaps
by you if you're interested.
Cheers,
Mike
--
Michael Droettboom
Science Software Branch
Space Telescope Science Institute
Baltimore, Maryland, USA
------------------------------------------------------------------------------
EditLive Enterprise is the world's most technically advanced content
authoring tool. Experience the power of Track Changes, Inline Image
Editing and ensure content is compliant with Accessibility Checking.
http://p.sf.net/sfu/ephox-dev2dev
_______________________________________________
Matplotlib-devel mailing list
Matplotlib-devel@lists.sourceforge.net
matplotlib-devel List Signup and Options
--
Michael Droettboom
Science Software Branch
Space Telescope Science Institute
Baltimore, Maryland, USA