[racket] big-bang is slow to render on screen?

For the record, Matthew pushed a fix involving `cairo_fill` and
`cairo_paint_with_alpha`:
https://github.com/plt/racket/commit/54e42664dfd2aeafbe41c2ff424d86affe171962

Laurent


On Mon, Apr 21, 2014 at 4:00 PM, Laurent <laurent.orseau at gmail.com> wrote:

> I have a 2htdp/universe program that used to run fast enough a few months
> ago, but now it is very slow and not usable.
> The slowness seems to be because of the on-screen rendering, and not
> because of the generation of the image.
>
> Here is a stripped-down version that shows this behavior:
> https://gist.github.com/Metaxal/11142941
>
> In the following log, you see that the `on-key` events are very close one
> to the other (in milliseconds after the beginning of the program), but the
> corresponding `to-draw` events are separated by more than a second, even
> though generating the image (cpu time) takes almost no time:
>
> on-key a at 6906
> on-key u at 6912
> on-key i at 6912
> on-key e at 6913
> to-draw at 6913
> to-draw: cpu time: 4 real time: 3 gc time: 0
> to-draw at 8598
> to-draw: cpu time: 4 real time: 2 gc time: 0
> to-draw at 11948
> to-draw: cpu time: 4 real time: 2 gc time: 0
> to-draw at 13631
> to-draw: cpu time: 0 real time: 2 gc time: 0
> to-draw at 161839
> to-draw: cpu time: 4 real time: 9 gc time: 0
>
> During those long seconds, Xorg is almost at 100% cpu.
>
> However, using an empty scene instead of an image is fast.
> The time also depends on the size of the grid.
>
> I'm using Ubuntu 12.04 64bits.
> I have tried to replicate the behavior on older versions of racket (5.3.1
> and 5.90.0.9) but it's the same. So maybe the problem is not on Racket's
> side but something has changed in Ubuntu?
>
> Does anyone else see the same behavior, either on the same platform or on
> a different one?
>
> Thanks,
> Laurent
>
>
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