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// calculate a normal vector from the paddle to the puck

CGPoint vector = normalVector(bottomPaddleData.puckLocation.x,

bottomPaddleData.paddleLocation.x, bottomPaddleData.puckLocation.y,

bottomPaddleData.paddleLocation.y);

double speed = paddleSpeed(bottomPaddleData);

vector.x = vector.x * speed;

vector.y = vector.y * speed;

// update the velocity of the puck

bottomPaddleData.puckVelocity.x = vector.x;

bottomPaddleData.puckVelocity.y = vector.y;

bottomPaddleData.intersect = true;

}

else

bottomPaddleData.intersect = false;

dist = distance(bottomPaddleData.puckLocation.x,

topPaddleData.paddleLocation.x, bottomPaddleData.puckLocation.y,

topPaddleData.paddleLocation.y);

if (!topPaddleData.intersect & dist < (PADDLE_RADIUS + PUCK_RADIUS)) {

// calculate a normal vector from the paddle to the puck

CGPoint vector = normalVector(bottomPaddleData.puckLocation.x,

topPaddleData.paddleLocation.x, bottomPaddleData.puckLocation.y,

topPaddleData.paddleLocation.y);

double speed = paddleSpeed(topPaddleData);

vector.x = vector.x * speed;

vector.y = vector.y * speed;

// update the velodity of the puck

bottomPaddleData.puckVelocity.x = vector.x;

bottomPaddleData.puckVelocity.y = vector.y;

bottomPaddleData.intersect = true;

}

else

bottomPaddleData.intersect = false;

// decay the velocity of the puck

if (bottomPaddleData.puckVelocity.x > 0.3)

bottomPaddleData.puckVelocity.x += -PUCK_DECAY_RATE;

else if (bottomPaddleData.puckVelocity.x < -0.3)

bottomPaddleData.puckVelocity.x += PUCK_DECAY_RATE;

if (bottomPaddleData.puckVelocity.y > 0.3)

bottomPaddleData.puckVelocity.y += -PUCK_DECAY_RATE;

else if (bottomPaddleData.puckVelocity.y < -0.3)

bottomPaddleData.puckVelocity.y += PUCK_DECAY_RATE;

// apply terminal velocity.

// the puck should not be traveling so fast that it can pass

// through the paddle without intersecting with it

if (bottomPaddleData.puckVelocity.x > PADDLE_RADIUS)

bottomPaddleData.puckVelocity.x = PADDLE_RADIUS;

else if (bottomPaddleData.puckVelocity.x < -PADDLE_RADIUS)

bottomPaddleData.puckVelocity.x = PADDLE_RADIUS;

if (bottomPaddleData.puckVelocity.y > PADDLE_RADIUS)

bottomPaddleData.puckVelocity.y = PADDLE_RADIUS;

else if (bottomPaddleData.puckVelocity.y < -PADDLE_RADIUS)

bottomPaddleData.puckVelocity.y = PADDLE_RADIUS;

// decay the rotation of the puck

if (bottomPaddleData.puckRotation > 0.001)

bottomPaddleData.puckRotation += -PUCK_SPIN_DECAY_RATE;

else if (bottomPaddleData.puckRotation < -0.001)

bottomPaddleData.puckRotation += PUCK_SPIN_DECAY_RATE;

// move the puck as prescribed by the rotation

bottomPaddleData.puckAngle += bottomPaddleData.puckRotation;

if (bottomPaddleData.puckAngle > 360.0)

bottomPaddleData.puckAngle = bottomPaddleData.puckAngle - 360.0;

// move the puck as prescribed by the velocity

bottomPaddleData.puckLocation.x += bottomPaddleData.puckVelocity.x;

bottomPaddleData.puckLocation.y += bottomPaddleData.puckVelocity.y;

// bounce the puck off left and right walls

if ((bottomPaddleData.puckLocation.x + PUCK_RADIUS) > 320) {

// invert the velocity

bottomPaddleData.puckVelocity.x = -bottomPaddleData.puckVelocity.x;

// move the puck back inbounds before it is drawn

bottomPaddleData.puckLocation.x = 320 - PUCK_RADIUS;

// change the rotation of the puck according to the angle and speed

// that it strikes the wall

bottomPaddleData.puckRotation +=

-(bottomPaddleData.puckVelocity.y * 0.005);

}

if ((bottomPaddleData.puckLocation.x - PUCK_RADIUS) < 0) {

bottomPaddleData.puckVelocity.x = -bottomPaddleData.puckVelocity.x;

bottomPaddleData.puckLocation.x = PUCK_RADIUS;

bottomPaddleData.puckRotation +=

(bottomPaddleData.puckVelocity.y * 0.005);

}

// bounce the puck off the top and bottom walls

if (!messageView) {

if ((bottomPaddleData.puckLocation.y + PUCK_RADIUS) > 480) {

// let the puck go if it is headed through the goal

if ((bottomPaddleData.puckLocation.x < GOAL_START)

| (bottomPaddleData.puckLocation.x > GOAL_END)) {

bottomPaddleData.puckVelocity.y = -bottomPaddleData.puckVelocity.y;

bottomPaddleData.puckLocation.y