Re: [Matplotlib-users] Animate on Mac O$

[Michiel de H. <mjl...@ya...>]

Hi Ryan,

In matplotlib, drawing is done as part of the call to figure.draw(renderer).
The MacOSX backend makes this call from the event loop callback
(i.e., the drawRect function in src/_macosx.m). Outside of the event loop
callback, the graphics context (CGContextRef on Macs) is undefined, and
no drawing can take place.

In the animations module, event_source is a timer that periodically calls
_step, which calls _draw_next_frame, which calls _post_draw to do the
blitting. But since the timer lives outside if the event loop, blitting will fail on
Macs; there simply is no graphics context to draw to.

The solution is to split the blitting into two parts:
- A front-end blitting function that tells matplotlib to blit
(this is the function called by the timer)
- A back-end blitting function that does the actual blitting
(as part of the call to figure.draw(renderer);
the back-end blitting function is implemented in the backend).

In a sense, this is the same as for the other graphics functions
(e.g. there is a front-end "plot" function, and a back-end "draw_path" function).

See the discussion here for more information:
https://github.com/matplotlib/matplotlib/issues/531
(this discussion also went into other issues though).

Best,
-Michiel.

--------------------------------------------
On Thu, 3/13/14, Ryan May <rm...@gm...> wrote:

 Subject: Re: [Matplotlib-users] Animate on Mac O$
 To: "Michiel de Hoon" <mjl...@ya...>
 Cc: "Christophe Bal" <pro...@gm...>, "Matplotlib" <mat...@li...>
 Date: Thursday, March 13, 2014, 8:29 PM
 
 > On Mar 13, 2014, at 17:55,
 Michiel de Hoon <mjl...@ya...>
 wrote:
 > 
 > The problems with animations on Mac
 > are not so much related to the backend,
 > but to the animations code itself. Animations
 > with the MacOSX backend cannot be fixed
 > without redesigning the animations module.
 
 Can you give me a better idea why you think so? I wrote the
 original and have a Mac now...
 
 Ryan