Question

I don’t know how the best way is to explain what I am trying to do, but I will give it a shot.
So I have a football on the screen and when I touch the screen I can drag my finger across the screen which by using a CCProgressTimer gives me a representation of the power of the throw. In other words it is like having a volume bar on the screen and when I touch the screen and drag away from the volume bar it starts to increase and dragging towards the volume bar decreases it. So my question is I am recording my touch when I touch the screen and that touch is what all the calculations are based off of, but I want to some how be able to no matter where I am on the screen be able to decrease or increase. The way it works right now is, I can’t start to decrease the power of the throw until I reach that recorded touch. Is it possible to have it work, where when the power is at %100 no matter where I am on the screen if I drag back towards the football to have it decrease before I reach that original touch on the screen. Here is my code.

    footballPath = [CCProgressTimer progressWithFile:@"footballPath.png"];
            footballPath.visible = NO;
            footballPath.percentage = 0;
            footballPath.type = kCCProgressTimerTypeHorizontalBarLR;
            footballPath.anchorPoint = ccp(0, 0.5);
            [self addChild:footballPath];

-(BOOL)ccTouchBegan:(UITouch*)touch withEvent:(UIEvent *)event {

    cachedTouchPt = [self convertTouchToNodeSpace:touch];

    if (!self.currentFootball.footballHasEmbarked) {
        footballPath.percentage = 0;
        [self updateArrowWithTouch:touch];
        arrow.visible = YES;
        footballPath.visible = YES;

        return YES; 
    }
    else {
        return NO;
    }

}

-(void) ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event {

    [self updateArrowWithTouch:touch];

}

-(void) ccTouchEnded:(UITouch*)touch withEvent:(UIEvent *)event {

    const float max = 100;
    CGPoint touchPt = [self convertTouchToNodeSpace:touch];
    if (touchPt.x > self.currentFootball.position.x) {
        touchPt = ccp(self.currentFootball.position.x, touchPt.y);
    }

    arrow.visible = NO;
    footballPath.visible = NO;
    self.currentFootball.footballHasEmbarked = YES;
    self.currentFootball.spiraling = YES;

    if (self.currentFootball) {
        [smgr morphShapeToActive:self.currentFootball.shape mass:25];
    }

    diff = ccpSub(touchPt, self.currentFootball.position);

    if (diff.x == 0 && diff.y == 0) {
        diff = ccp(1, 1);
    }
    float len = footballPath.percentage;
    CGPoint norm = ccpNormalize(diff);

    if (len > max){
        len = max;
    }

    [self.currentFootball applyImpulse:ccpMult(norm, (len * 245))];

    pos = self.currentFootball.position.y;

    [self schedule:@selector(newFootball)]; 

}

- (void) updateArrowWithTouch: (UITouch*) touch {

    const float distFromFb = 100;
    CGPoint touchPt = [self convertTouchToNodeSpace:touch];
    if (touchPt.x > self.currentFootball.position.x) {
        touchPt = ccp(self.currentFootball.position.x, touchPt.y);
    }

    CGPoint fpt = self.currentFootball.position;

    CGPoint vect = ccpSub(touchPt, fpt);
    float dist = ccpLength(vect);
    CGPoint vect2 = ccpSub(touchPt, cachedTouchPt);
    float dist2 = ccpLength(vect2);
    float degrees = -CC_RADIANS_TO_DEGREES(ccpToAngle(vect));
    float factor = dist2;
    CGPoint normalVect = ccpMult(vect, 1/dist);

    factor = distFromFb;

    CGPoint newPoint = ccpAdd(fpt, ccpMult(normalVect, factor));
    if (newPoint.x < self.currentFootball.position.x+1) {
        arrow.rotation = degrees; 
        arrow.position = newPoint;

        self.currentFootball.rotation = -CC_RADIANS_TO_DEGREES (ccpToAngle(ccpSub(touchPt, self.currentFootball.position)));
        footballPath.rotation = self.currentFootball.rotation;
        footballPath.position = fpt;
    }   

    float percentage = dist - ccpLength(ccpSub(cachedTouchPt, self.currentFootball.position));

    if (percentage < 0.0f){

        percentage = 0.0f;
    }

//  CCLOG(@"cachedDist = %f", cachedDist);
    CCLOG(@"percentage = %f", percentage);

        diff = vect2;
        footballPath.percentage = percentage;

}

The cachedTouchPt = [self convertTouchToNodeSpace:touch]; is the original point that I am talking about. So when I touch the screen it makes a new point and stores it in cachedTouchPt, and so I can’t decrease the the power/CCProgressTimer until I reach the X and Y of the cachedTouchPt. If I didn’t make sense of what I was trying to say. I need to be able to decrease the power/CCProgressTimer without needing to be at the original point. Is there a way reset the point so that no matter where I am on the screen I can drag towards the football and have it decrease, same with the increasing.

Answer 1

I’ll answer your question by showing you the math but you need to convert it to codes yourself.

First, you need to decide (you probably did) how long (in points) does a touch need to move to increase the power of the throw from 0 to 1. Let’s refer to this value as D.

Then, let’s refer to the coordinate where the touch began as Tx and Ty.

Then, when the touch moved to new coordinate Ux and Uy, you the distance the touch has moved from (Tx, Ty) using formula:

E = sqrt( pow( Ux - Tx, 2 ) + pow( Uy - Ty, 2 ) )

And you calculate the power using formula:

P = E / D

Up to this point I think your code is already doing all these calculations. But what’s coming next is how you would handle if player still moves the touch exceeding the distance D from the touch began point, that is to say that E > D.

First, put an IF block:

if (E > D) { ... }

So, now you want to modify Tx and Ty values (i.e. the touch began point) so that the distance from the current touch position to that coordinate is D. Here’s the magic formula:

angle = atan2( Uy - Ty, Ux - Tx )
Ty = Uy - D * sin( angle )
Tx = Ux - D * cos( angle )

At this point you might want to modify the power value to 1:

P = 1
E = D

And that’s it! The formula will move the touch began point towards the current touch position to maintain the condition of E <= D. Naturally the case where the player moves the touch towards the touch began point is taken care of.

Good luck!