iOS animations using CADisplayLink - objective-c

Question

I'm using animation and timing with CADisplayLink. When the ball touches a big stone it is removed immediately. How can I animate the removal of the stone (block) like exploding to small stones? Here's the code I currently have:
- (void)checkCollisionWithBlocks
{
for (BlockView *bv in blocks) {
if (CGRectIntersectsRect(bv.frame, ballRect)) {
ballVelocity.y = -ballVelocity.y;
[blocks removeObject:bv];
[bv removeFromSuperview];
break;
}
}
}

Answer 1

CADisplayLink is really a bit... much for what you're planning (it's for synchronizing screen drawing updates to a custom animation). Here's my solution: set some things on fire! While it's not necessarily an explosion, this will cause your block to belch some blue fire (you can change the color by modifying self.fireColor).
- (void)checkCollisionWithBlocks
{
for (BlockView *bv in blocks) {
if (CGRectIntersectsRect(bv.frame, ballRect)) {
ballVelocity.y = -ballVelocity.y;
[blocks removeObject:bv];
[bv burpFire]
[bv removeFromSuperview];
break;
}
}
}
#interface BlockView : UIView
#property (nonatomic, strong) CALayer *rootLayer;
#property (nonatomic, strong) CAEmitterLayer *fireEmitter;
#property (nonatomic, strong) CAEmitterLayer *smokeEmitter;
#property (nonatomic, strong) UIColor *fireColor;
#property (nonatomic, strong) UIColor *smokeColor;
-(void)burpFire;
#end
#implementation BlockView
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
self.rootLayer = [CALayer layer];
//Set the root layer's background color to black
self.rootLayer.backgroundColor = [UIColor blackColor].CGColor;
//Create the fire emitter layer
self.fireEmitter = [CAEmitterLayer layer];
self.fireEmitter.emitterPosition = CGPointMake(0, CGRectGetMaxY(frame) + 50);
self.fireEmitter.emitterMode = kCAEmitterLayerOutline;
self.fireEmitter.emitterShape = kCAEmitterLayerLine;
self.fireEmitter.renderMode = kCAEmitterLayerAdditive;
self.fireEmitter.emitterSize = CGSizeMake(0, 0);
//Create the smoke emitter layer
self.smokeEmitter = [CAEmitterLayer layer];
self.smokeEmitter.emitterPosition = CGPointMake(0, CGRectGetMaxY(frame) + 50);
self.smokeEmitter.emitterMode = kCAEmitterLayerPoints;
//Create the fire emitter cell
CAEmitterCell* fire = [CAEmitterCell emitterCell];
fire.emissionLongitude = M_PI;
fire.birthRate = 0;
fire.velocity = -80;
fire.velocityRange = -30;
fire.emissionRange = -1.1;
fire.yAcceleration = -200;
fire.scaleSpeed = 0.3;
self.fireColor = [UIColor colorWithRed:0.425 green:0.779 blue:0.800 alpha:0.100];
fire.color = self.fireColor.CGColor;
fire.contents = (id)[self CGImageNamed:#"fire.png"];
//Name the cell so that it can be animated later using keypaths
[fire setName:#"fire"];
//Add the fire emitter cell to the fire emitter layer
self.fireEmitter.emitterCells = [NSArray arrayWithObject:fire] ;
//Create the smoke emitter cell
CAEmitterCell* smoke = [CAEmitterCell emitterCell];
smoke.birthRate = 11;
smoke.emissionLongitude = M_PI / 2;
smoke.lifetime = 0;
smoke.velocity = -40;
smoke.velocityRange = 20;
smoke.emissionRange = M_PI / 4;
smoke.spin = 1;
smoke.spinRange = 6;
smoke.yAcceleration = 160;
smoke.contents = (id) [self CGImageNamed:#"smoke.png"];
smoke.scale = 0.1;
smoke.alphaSpeed = -0.12;
smoke.scaleSpeed = 0.7;
//Name the cell so that it can be animated later using keypaths
[smoke setName:#"smoke"];
//Add the smoke emitter cell to the smoke emitter layer
self.smokeEmitter.emitterCells = [NSArray arrayWithObject:smoke];
//Add the two emitter layers to the root layer
[self.layer addSublayer:self.smokeEmitter];
[self.layer addSublayer:self.fireEmitter];
[self burpFire];
}
return self;
}
//Return a CGImageRef from the specified image file in the app's bundle
-(CGImageRef)CGImageNamed:(NSString*)name {
NSString *url = [[NSBundle mainBundle] pathForResource:name ofType:nil];
return [UIImage imageWithContentsOfFile:url].CGImage;
}
-(void)burpFire {
float gas = 80.0 / 100.0;
//Update the fire properties
[self.fireEmitter setValue:[NSNumber numberWithInt:(gas * 1000)] forKeyPath:#"emitterCells.fire.birthRate"];
[self.fireEmitter setValue:[NSNumber numberWithFloat:gas] forKeyPath:#"emitterCells.fire.lifetime"];
[self.fireEmitter setValue:[NSNumber numberWithFloat:(gas * 0.35)] forKeyPath:#"emitterCells.fire.lifetimeRange"];
self.fireEmitter.emitterSize = CGSizeMake(100 * gas, 0);
//Update the smoke properites
[self.smokeEmitter setValue:[NSNumber numberWithInt:gas * 4] forKeyPath:#"emitterCells.smoke.lifetime"];
self.smokeColor = [UIColor colorWithRed:1 green:1 blue:1 alpha:gas * 0.3];
[self.smokeEmitter setValue:(__bridge id)self.smokeColor.CGColor forKeyPath:#"emitterCells.smoke.color"];
[self setNeedsDisplay];
[self performSelector:#selector(burpFinished) withObject:nil afterDelay:1.5];
}
-(void)burpFinished {
float gas = 0.0 / 100.0;
//Update the fire properties
[self.fireEmitter setValue:[NSNumber numberWithInt:(gas * 1000)] forKeyPath:#"emitterCells.fire.birthRate"];
[self.fireEmitter setValue:[NSNumber numberWithFloat:gas] forKeyPath:#"emitterCells.fire.lifetime"];
[self.fireEmitter setValue:[NSNumber numberWithFloat:(gas * 0.35)] forKeyPath:#"emitterCells.fire.lifetimeRange"];
self.fireEmitter.emitterSize = CGSizeMake(100 * gas, 0);
//Update the smoke properites
[self.smokeEmitter setValue:[NSNumber numberWithInt:gas * 4] forKeyPath:#"emitterCells.smoke.lifetime"];
self.smokeColor = [UIColor colorWithRed:1 green:1 blue:1 alpha:gas * 0.3];
[self.smokeEmitter setValue:(__bridge id)self.smokeColor.CGColor forKeyPath:#"emitterCells.smoke.color"];
}
The CAEmitterLayers last for quite a while, so if you want the fire to shut off a little faster, play around with the timing of the stop selector. If you want smaller or larger fire, or fireballs that stick around longer, play around with the properties in the init method, either way you're gonna get a cool effect.
All colors must be strong references to UIColor, else Core Animation will freak out and throw a C++ temper tantrum in your debugger... not pleasant.