用CAEmitterLayer实现粒子动画飘雪花效果

// Configure the particle emitter to the top edge of the screen

CAEmitterLayer *snowEmitter = [CAEmitterLayer layer];

snowEmitter.emitterPosition = CGPointMake(self.view.bounds.size.width / 2.0, -30);

snowEmitter.emitterSize = CGSizeMake(self.view.bounds.size.width * 2.0, 0.0);;

// Spawn points for the flakes are within on the outline of the line

snowEmitter.emitterMode = kCAEmitterLayerOutline;

snowEmitter.emitterShape = kCAEmitterLayerLine;

// Configure the snowflake emitter cell

CAEmitterCell *snowflake = [CAEmitterCell emitterCell];

snowflake.birthRate = 10.0;//粒子产生速率

snowflake.lifetime = 120.0;//粒子的生命时间

snowflake.velocity = -300; //粒子发射速度 // falling down slowly

snowflake.velocityRange = 5;

snowflake.yAcceleration = 2;

snowflake.emissionRange = 0.5 * M_PI; // some variation in angle

snowflake.spinRange = 0.25 * M_PI; // slow spin

snowflake.contents = (id) [[UIImage imageNamed:@"DazFlake"] CGImage];

snowflake.color = [[UIColor colorWithRed:0.600 green:0.658 blue:0.743 alpha:1.000] CGColor];

// Make the flakes seem inset in the background

snowEmitter.shadowOpacity = 1.0;

snowEmitter.shadowRadius  = 0.0;

snowEmitter.shadowOffset  = CGSizeMake(0.0, 1.0);

snowEmitter.shadowColor   = [[UIColor whiteColor] CGColor];

// Add everything to our backing layer below the UIContol defined in the storyboard

snowEmitter.emitterCells = [NSArray arrayWithObject:snowflake];

[self.view.layer insertSublayer:snowEmitter atIndex:0];