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PONot a number error (NAN) doing collision detection in an iphone app
 

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  1. PONot a number error (NAN) doing collision detection in an iphone app
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    <p>I have a set of balloons that I am trying to get to bounce off of each other like balls. When I start to move them and then detect collision, the routine for the collisions eventually returns a NAN for the velocity of the balloons. I end up with a position of something like x=270, y= -nan(0x400000). I've been looking at the code all day and I still can't find the error, any help would be appreciated. Here's the code:</p> <pre><code> - (void)MoveBalloons { for (CurBalloon=1; CurBalloon &lt;= NumBalloons; ++CurBalloon) { //check for edge hCurBalloont if (uBalloon[CurBalloon].pos.y &gt; 456) { uBalloon[CurBalloon].pos.y = 456; uBalloon[CurBalloon].Vel_y = -uBalloon[CurBalloon].Vel_y; } if (uBalloon[CurBalloon].pos.y &lt; 24) { uBalloon[CurBalloon].pos.y = 24; uBalloon[CurBalloon].Vel_y = -uBalloon[CurBalloon].Vel_y; } if (uBalloon[CurBalloon].pos.x &gt; 289) { uBalloon[CurBalloon].pos.x = 289; uBalloon[CurBalloon].Vel_x = -uBalloon[CurBalloon].Vel_x; } if (uBalloon[CurBalloon].pos.x &lt; 31) { uBalloon[CurBalloon].pos.x = 31; uBalloon[CurBalloon].Vel_x = -uBalloon[CurBalloon].Vel_x; } //call loop to go through the balloons for each touch. //[self CollisionCheck]; NSUInteger h; float dist, tempvelx, tempvely, temp2velx, temp2vely;; for (h=1; h &lt;= NumBalloons; ++h) { //check if balloon is too close if (CurBalloon == h) { //skip the check ifit's the same balloon } else { dist = distanceBetweenPoints(uBalloon[CurBalloon].pos, uBalloon[h].pos); if (dist &lt;= (kBalloonNear)) { //balloon's touching tempvelx = uBalloon[CurBalloon].Vel_x; tempvely = uBalloon[CurBalloon].Vel_y; temp2velx = uBalloon[h].Vel_x; temp2vely = uBalloon[h].Vel_y; tempvelx = (uBalloon[CurBalloon].Vel_x - uBalloon[h].Vel_x) * (sinf(angleBetweenPoints(uBalloon[CurBalloon].pos,uBalloon[h].pos)))*(uBalloon[CurBalloon].Vel_x - uBalloon[h].Vel_x) * (sinf(angleBetweenPoints(uBalloon[CurBalloon].pos,uBalloon[h].pos))) - (uBalloon[CurBalloon].Vel_y - uBalloon[h].Vel_y) * sinf(angleBetweenPoints(uBalloon[CurBalloon].pos, uBalloon[h].pos)) * cosf(angleBetweenPoints(uBalloon[CurBalloon].pos, uBalloon[h].pos)) + uBalloon[h].Vel_x; tempvely = (uBalloon[CurBalloon].Vel_y - uBalloon[h].Vel_y) * (cosf(angleBetweenPoints(uBalloon[CurBalloon].pos,uBalloon[h].pos))) * (uBalloon[CurBalloon].Vel_y - uBalloon[h].Vel_y) * (cosf(angleBetweenPoints(uBalloon[CurBalloon].pos,uBalloon[h].pos))) - (uBalloon[CurBalloon].Vel_x - uBalloon[h].Vel_x) * sinf(angleBetweenPoints(uBalloon[CurBalloon].pos, uBalloon[h].pos)) * cosf(angleBetweenPoints(uBalloon[CurBalloon].pos, uBalloon[h].pos)) + uBalloon[h].Vel_y; temp2velx = (uBalloon[CurBalloon].Vel_x - uBalloon[h].Vel_x) * (cosf(angleBetweenPoints(uBalloon[CurBalloon].pos,uBalloon[h].pos))) * (uBalloon[CurBalloon].Vel_x - uBalloon[h].Vel_x) * (cosf(angleBetweenPoints(uBalloon[CurBalloon].pos,uBalloon[h].pos))) + (uBalloon[CurBalloon].Vel_y - uBalloon[h].Vel_y) * sinf(angleBetweenPoints(uBalloon[CurBalloon].pos, uBalloon[h].pos)) * cosf(angleBetweenPoints(uBalloon[CurBalloon].pos, uBalloon[h].pos)) + uBalloon[h].Vel_x; temp2vely = (uBalloon[CurBalloon].Vel_y - uBalloon[h].Vel_y) * (sinf(angleBetweenPoints(uBalloon[CurBalloon].pos,uBalloon[h].pos)))*(uBalloon[CurBalloon].Vel_y - uBalloon[h].Vel_y) * (sinf(angleBetweenPoints(uBalloon[CurBalloon].pos,uBalloon[h].pos))) - (uBalloon[CurBalloon].Vel_x - uBalloon[h].Vel_x) * sinf(angleBetweenPoints(uBalloon[CurBalloon].pos, uBalloon[h].pos)) * cosf(angleBetweenPoints(uBalloon[CurBalloon].pos, uBalloon[h].pos)) + uBalloon[h].Vel_y; uBalloon[CurBalloon].Vel_x = tempvelx; uBalloon[CurBalloon].Vel_y = tempvely; uBalloon[h].Vel_x = temp2velx; //set to old value of CurBalloon balloon. uBalloon[h].Vel_y = temp2vely; } } } if (fabsf(uBalloon[CurBalloon].Vel_x) &gt;= kBalloonMaxSpeed) uBalloon[CurBalloon].Vel_x = kBalloonMaxSpeed; if (fabsf(uBalloon[CurBalloon].Vel_y) &gt;= kBalloonMaxSpeed) uBalloon[CurBalloon].Vel_y = kBalloonMaxSpeed; if (fabsf(uBalloon[CurBalloon].Vel_x) &lt;= -kBalloonMaxSpeed) uBalloon[CurBalloon].Vel_x = -kBalloonMaxSpeed; if (fabsf(uBalloon[CurBalloon].Vel_y) &lt;= -kBalloonMaxSpeed) uBalloon[CurBalloon].Vel_y = -kBalloonMaxSpeed; if (uBalloon[CurBalloon].Vel_y &gt; KBalloonSpeed) { //if travellCurBalloonng fast, slow CurBalloont up fast to normal speed uBalloon[CurBalloon].Vel_y = uBalloon[CurBalloon].Vel_y - kBalloonSlowRate; } if (uBalloon[CurBalloon].Vel_x &gt; KBalloonSpeed) { //if travellCurBalloonng fast, slow CurBalloont up fast to normal speed uBalloon[CurBalloon].Vel_x = uBalloon[CurBalloon].Vel_x - kBalloonSlowRate; } if (uBalloon[CurBalloon].Vel_y &lt; KBalloonSpeed) { //if travellCurBalloonng fast, slow CurBalloont up fast to normal speed uBalloon[CurBalloon].Vel_y = uBalloon[CurBalloon].Vel_y + kBalloonSlowRate; } if (uBalloon[CurBalloon].Vel_x &lt; KBalloonSpeed) { //if travellCurBalloonng fast, slow CurBalloont up fast to normal speed uBalloon[CurBalloon].Vel_x = uBalloon[CurBalloon].Vel_x + kBalloonSlowRate; } //slow to 0 if velocCurBalloonty CurBalloons CurBalloonnsCurBalloonde the slow rate if (fabsf(uBalloon[CurBalloon].Vel_x) &lt;= kBalloonSlowRate) uBalloon[CurBalloon].Vel_x = 0; if (fabsf(uBalloon[CurBalloon].Vel_y) &lt;= kBalloonSlowRate) uBalloon[CurBalloon].Vel_y = 0; uBalloon[CurBalloon].Vel_x = uBalloon[CurBalloon].Vel_x - kBalloonFallRate; //keep movCurBalloonng down //add velocCurBalloonty to poCurBalloonnts uBalloon[CurBalloon].pos.y= uBalloon[CurBalloon].pos.y + uBalloon[CurBalloon].Vel_y; uBalloon[CurBalloon].pos.x = uBalloon[CurBalloon].pos.x + uBalloon[CurBalloon].Vel_x; } } </code></pre> <p>Here's the functions written in c that are used for distance and the angle. I'm even making sure to never have a sqrt(-1) and division by 0: </p> <pre><code> CGFloat distanceBetweenPoints (CGPoint first, CGPoint second) { CGFloat deltaX = second.x - first.x; CGFloat deltaY = second.y - first.y; if ((deltaX*deltaX + deltaY*deltaY ) == -1) { return sqrtf(-.99); } else { return sqrtf(deltaX*deltaX + deltaY*deltaY ); } } CGFloat angleBetweenPoints(CGPoint first, CGPoint second) { if (first.x - second.x == 0) { return (pi / 2); } else { return atanf((first.y-second.y) / (first.x - second.x)); } } </code></pre>
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