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break loop with keypress

3 messages · William Simpson, Greg Snow

William Simpson
# 
This works, but it is not quite what I need:

par(mar=rep(0,4))

while(1)
  {
  img1<-matrix(runif(2500),50,50)
  dev.hold(); image(img1,useRaster=TRUE); dev.flush()
  img2<-matrix(runif(2500),50,50)
  dev.hold(); image(img2,useRaster=TRUE); dev.flush()
  }

I would like to do this:
while(!kbhit())
  {
  ...

where kbhit() polls the keyboard, returning a non-zero integer if the
keyboard buffer has something in it. The animation loop continues
until a key is pressed.

All the ways of getting user input I have seen (e.g. getGraphicsEvent)
are not suitable because they would wait on each pass through the loop
until the key is pressed and therefore no animation would be
presented.

Any ideas on how to present a continuous animation loop which is
broken upon user input (keypress or mouse button press)? I am using
Windows 7. Thanks very much for any help.

Bill
Greg Snow
# 
You could create a tcltk window that looks for a button click and/or
key press and when that happens change the value of a variable.  Then
in your loop you just look at the value of the same variable and break
when the value changes.

On Tue, Aug 5, 2014 at 6:13 AM, William Simpson
<william.a.simpson at gmail.com> wrote:

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      William Simpson
    

    

      
      #
    

  


  

      
Thanks Greg.
I guess another option is to call a C function directly. On Windows I
see there is a function _kbhit() in conio.h. Not sure if it would be
that simple.
Write a .c file

#include <conio.h>

int main(void)
{
  int ch;
  ch= _kbhit();
  return ch;
}

Then do the necessary stuff to call that from R.
http://mazamascience.com/WorkingWithData/?p=1067

Bill

        
On 06/08/2014, Greg Snow <538280 at gmail.com> wrote: