Updating emitter.gravity on a CCParticleSystemQuad on touch event - iphone

Question

I've created a simple cocos2d iPhone game that has a CCParticleSystemQuad emitter that emits particles across the scene that are shaped like leaves, to give the illusion of wind.
Right now, the wind (gravity) is blowing across the scene from right to left. I am currently stuck trying to figure out how to update the emitter.gravity to switch from (-500, 80) to (500, 80), hopefully without removing the particles that have already been drawn.
In this example, I'd like the switch to occur on a touch event that happens anywhere on the screen.
What should my touch event look like?
How do I detect a touch that happens any where on the screen?
I've also never implemented a scheduled update loop. Is this the direction I should be thinking? And I suppose a more basic question is, am I going about this the right way?
Here's the code I've got so far:
My init:
-(id) init
{
if( (self=[super init])) {
CCSprite * sky = [CCSprite spriteWithFile:#"sky.png"];
[self addChild:sky z:0 tag:1];
windDirection = -200;
[self leaveEmitters];
}
return self;
}
My leaveEmiiters function
-(void) leaveEmitters{
NSLog(#"The wind is :%i", windDirection);
CCParticleSystemQuad * emitter;
emitter = [[CCParticleSystemQuad alloc] initWithTotalParticles:100];
emitter.texture = [[CCTextureCache sharedTextureCache] addImage: #"particlesLeaves.png"];
emitter.emitterMode = kCCParticleModeGravity;
emitter.duration = -1;
emitter.gravity = ccp(windDirection, -80);
emitter.angle = 0;
emitter.angleVar = 360;
emitter.speed = 10;
emitter.speedVar = 100;
emitter.radialAccelVar = 0;
emitter.tangentialAccel = 0;
emitter.tangentialAccelVar = 0;
emitter.life = 10;
emitter.lifeVar = 0;
emitter.startSpin = 0;
emitter.startSpinVar = 360;
emitter.endSpin = 0;
emitter.endSpinVar = 720;
ccColor4F startColorVar = {255, 100, 0, 0};
ccColor4F startColor = {0, 240,0, 255};
emitter.startColor = startColor;
emitter.startColorVar = startColorVar;
emitter.endSize = emitter.startSize;
emitter.startSize = 60.0f;
emitter.emissionRate = 3;
emitter.blendAdditive = NO;
emitter.position = ccp(500,250);
[self addChild: emitter z:10];
emitter.autoRemoveOnFinish = YES;
CCParticleSystemQuad * emitter2;
emitter2 = [[CCParticleSystemQuad alloc] initWithTotalParticles:100];
emitter2.texture = [[CCTextureCache sharedTextureCache] addImage: #"particlesLeaves.png"];
emitter2.emitterMode = kCCParticleModeGravity;
emitter2.duration = -1;
emitter2.gravity = ccp(windDirection, 0);
emitter2.angle = 0;
emitter2.angleVar = 360;
emitter2.speed = 10;
emitter2.speedVar = 100;
emitter2.radialAccelVar = 0;
emitter2.tangentialAccel = 0;
emitter2.tangentialAccelVar = 0;
emitter2.life = 10;
emitter2.lifeVar = 0;
emitter2.startSpin = 0;
emitter2.startSpinVar = 360;
emitter2.endSpin = 0;
emitter2.endSpinVar = 720;
emitter2.startColor = startColor;
emitter2.endSize = emitter.startSize;
emitter2.startSize = 60.0f;
emitter2.emissionRate = 3;
emitter2.blendAdditive = NO;
emitter2.position = ccp(-500,250);
[self addChild: emitter2 z:10];
emitter2.autoRemoveOnFinish = YES;
}
And finally, my ccTouchesBegan function, which isn't working at all. Why?
-(void) ccTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
CGPoint location = [touch locationInView:[touch view]];
location = [[CCDirector sharedDirector] convertToGL:location];
int x = location.x;
int y= location.y;
CCSprite * sky = (CCSprite *) [self getChildByTag:1];
sky.anchorPoint = ccp(0, 0);
CGRect skyHitBox = CGRectMake(sky.position.x, sky.position.y, 500, 500);
if (CGRectContainsPoint(skyHitBox, location)) {
NSLog(#"touch accepted: x: %i y:%i", x, y);
}
}
Any help, feedback, or suggested learning direction would be GREATLY appreciated. Thanks so much!
EDIT: I answered my own questions like 20 seconds after I posted this...
If someone wants to post their own answers, I'll leave this up for 7 more hours.

Answer 1

you just can keep a CCParticleSystemQuad * emitter as private instance member so you can modify emitter.gravity inside the ccTouchesBegan
i didnt get exactly what kind of wind effect you'r trying to achieve. If you want to simply switch from one 500,80 to -500,80 its pretty easy
emitter.gravity = ccp(-emitter.gravity.x, emitter.gravity.y);
If you want to change the wind direction based on witch side of the skybox you hit, with hitting the center equal no wind, and more your touch is far from the center the stronger the wind will get.
I didnt try this but should be a good starting point.
You first need to get get the touched point in skybox coordinates
CGPoint skyTouchedPoint = ccp( x - sky.position.x, y - sky.position.y)
then you can define the center point of you sky box as
CGPoint skyCenterPoint = ccp(sky.size.width/2, sky.size.height/2);
and get a vector pointing to the right side, if you touch the right half side of the skybox and pointing left if you touch the left half side of the skybox
CGPoint windDirection = ccpSub(skyTouchedPoint, skyCenterPoint);
this vector module is higher the more far from the center you touch happened, you should now increase this vector module by a factor that suites for you with
windDirection = ccpMult(windDirection, 10.f); //try different values here
now you can use only the x component of this vector if you want the wind to use always the same y (as you posted the value of 80)