cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   genericrich
   Member

   I need to be able to do per-pixel touch detection on a Sprite.

   The example using TouchDispatch protocol uses a rect-based system, which works good for rectangle-based sprites, but not for ones which aren't square.

   For example, I have a bunch of PNG files with triangles in them, against a transparent background. If I draw them as sprites, and tile them so that they are edge to edge (flipping every even triangle), then there will be triangles who can't be tapped, if we use a rect-based criteria.

   The old-school way of doing it in 8-bit days was to do a bitmask, so you would pregenerate an array of ints, say, from a sprite, so that you could just inspect that array for the corresponding value for that pixel. So pixels with your transparent color (purple) would be assigned a value of 0, and any other value would be assigned a value of 1. Then, just ask the array for the value that corresponds to your X * Y of the click coordinates, and return YES or NO when asked if that coord represents a hit.

   I could probably do the same thing using Cocos, but it seems like a kludge given the sophistication of the library. Does anybody know if there is an easier way using Cocos?

   Posted 2 years ago #
2. 

   adik
   Member

   Hi,

   If u want to detect touches in a polygonal shape, here is a code snippet from my project:

   -----
   /*
   returns YES if point is inside a poly shape, NO if point is not inside a poly shape
   */
   +(BOOL)pointInPolygon:(CGPoint*)poly polySides:(int)numberOfPolySides pointInside:(CGPoint)point {

   int i, j = numberOfPolySides-1 ;
   BOOL oddNodes = NO;

   for (i=0; i < numberOfPolySides; i++) {
   if (poly[i].y < point.y && poly[j].y >= point.y || poly[j].y < point.y && poly[i].y >= point.y) {
   if (poly[i].x + (point.y - poly[i].y) / (poly[j].y - poly[i].y) * (poly[j].x - poly[i].x ) < point.x ) {
   oddNodes = !oddNodes;
   }
   }
   j=i;
   }

   return oddNodes;

   }
   ---------

   This function accepts 3 params: array of CGPoints that make up ur poly shape, number of points that make up ur poly, and a point, which u want to determine if it is within the bounds of ur poly shape. Hope it helps.

   Posted 2 years ago #

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