From: Joel VanderWerf <vjoel@...>
Date: 2006-12-13T02:04:47+09:00
Subject: Re: TkCanvas on windows seems slow

Joel VanderWerf wrote:
> 
> Hi, all,
> 
> On linux, I developed a little Tk animation using TkCanvas, and then I 
> ran it on windows. It's much slower on windows than on linux (maybe, 
> 5fps versus 30fps). Same machine, but ruby-1.8.4 on linux, 1.8.5 on 
> windows.
> 
> The Windows Task Manager says the process is only using a tiny fraction 
> of cpu, so that's not the problem.
> 
> The canvas is currently just about a dozen objects, nothing special 
> (polygons, lines, etc.).
> 
> It does have two threads, one doing Tk.mainloop, and one sending 
> commands to the canvas. Increasing the priority of the command thread 
> makes it worse: Tk doesn't even seem to run--no windows. Decreasing the 
> priority makes it even slower.
> 
> Nothing is waiting on terminal input (I know that's a problem on windows).
> 
> I tried using a TkTimer instead, but couldn't get it to work at all.
...

Ok, I've got a workaround. I think the problem is that the command 
thread (the one sending commands to the canvas) isn't getting enough 
chances to run.

The workaround is to fire a very frequent task from the mainloop to 
explicitly hand control to the command thread:

3.times do
   timer = TkTimer.new(1) do
     3.times {thread.run}
   end

   timer.start
end

The two threes was necessary on my system to get full CPU utilization. 
Reducing either one of them resulted in using less CPU and having a 
lower frame rate. The 1ms clock cycle also seems to be necessary.

With this workaround the animation runs at the same speed as on linux, 
about 60fps. That's a lot better than the 6 fps without the hack.

I wish I knew whether this was a problem in ruby, tkruby, or windows...

Hope this helps someone else.

-- 
        vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407