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Index › Programming Questions & Help › Other Libraries › MULTITOUCH ROTATION IMAGE
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MULTITOUCH ROTATION IMAGE (Read 581 times)
mrdig
MULTITOUCH ROTATION IMAGE
Oct 23rd, 2008, 1:38pm  
Hi there,

I'm working with a multitouch system with blobs recognition and i want to rotate one image with the information of two blobs. (like iphone style)
How can i know, with two blobs points, that i'm rotating to right/left??
I'm not very good in maths, but i think, i have to calculate the angle of the vector of the two blobs point?
Would some help me please?
thanks,

RBOY
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mots
Re: MULTITOUCH ROTATION IMAGE
Reply #1 - Oct 23rd, 2008, 2:52pm  
it depends on which reference you are Wink

http://www.allegro.cc/forums/thread/591460

or something similar Smiley you reference would be something like ax=0,ay=1

float get_angle_between_in_radians(float ax, float ay, float bx, float by)
{
  float dotproduct, lengtha, lengthb, result;

  dotproduct = (ax * bx) + (ay * by);
  lengtha = sqrt(ax * ax + ay * ay);
  lengthb = sqrt(bx * bx + by * by);

  result = acos( dotproduct / (lengtha * lengthb) );

  if(dotproduct < 0)
  {
     if(result > 0)
        result += M_PI;
     else
        result -= M_PI;
  }
  return result;
}
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seltar
Re: MULTITOUCH ROTATION IMAGE
Reply #2 - Oct 23rd, 2008, 5:12pm  
You can find code for it in ActionScript here:
http://code.google.com/p/touchlib/source/browse/#svn/trunk/AS3

It's hidden in a lot of classes that extend other classes, so you're gonna have to start ripping out the stuff that matters.

Good luck Smiley
Let us know how you're coming along.

seltar
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mrdig
Re: MULTITOUCH ROTATION IMAGE
Reply #3 - Oct 23rd, 2008, 6:33pm  
thanks!
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antiplastik
Re: MULTITOUCH ROTATION IMAGE
Reply #4 - Oct 24th, 2008, 8:41pm  
atan2() might help, maybe?
http://processing.org/reference/atan2_.html
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mrdig
Re: MULTITOUCH ROTATION IMAGE
Reply #5 - Oct 25th, 2008, 10:29am  
the problem with atan2 is that only calculates one point.
any ideas?
cheers.
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