OperateParticleWithCodes

【OperateParticleWithCodes】

　　Listing 6-6 shows how you might configure an emitter’s scale property. This is a simplified version of a node’s xScale and yScale properties, and determines how large the particle is.

　　

【Using Keyframe Sequences to Configure Custom Ramps for a Particle Property】

　　

【Adding Actions to Particles】

　　Although you do not have direct access to the particles created by Sprite Kit, you can specify an action that all particles execute. Whenever a new particle is created, the emitter tells the particle to run that action. You can use actions to create very sophisticated behaviors.

　　For the purpose of using actions on particles, you can treat the particle as if it were a sprite. This means you can perform other interesting tricks, such as animating the particle’s textures.

【Using Target Nodes to Change the Destination of Particles】

　　When an emitter has a target node, it calculates the position, velocity, and orientation of the particle, exactly as if it were a child of the sprite node. This means that if the ship sprite is rotated, the exhaust orientation is automatically rotated also. However, at the moment a new particle’s starting values are calculated, the values are transformed into the target node’s coordinate system. Thereafter, they would only be affected by changes to the target node.

【Particle Emitter Tips】

　　Particle emitters in Sprite Kit are one of the most powerful tools for building visual effects. However, used incorrectly, particle emitters can be a bottleneck in the design and implementation of your app. Consider the following tips:

• Use Xcode to create and test your particle effects, then load the archives in your game.
• Adjust emitter properties sparingly inside your game code. Typically, you do this to specify properties that cannot be specified in the Xcode inspector or to control properties inside your game logic.
• Particles are cheaper than a sprite node, but they still have overhead! Try to keep the number of particles onscreen to a minimum by creating particle emitters with a low birth rate, and specifying a short lifetime for particles. For example, instead of creating hundreds or thousands of particles per second, reduce the birth rate and increase the size of the particles slightly. Often, you can create effects with fewer particles but the same net visual appearance.
• Use actions on particles only when there isn’t another solution. Executing actions on individual particles is potentially very expensive, especially if the particle emitter also has a high birth rate.
• Assign a target node whenever the particles should be independent of the emitter node after they are spawned. For examples, particles should be independent if the emitter node moves or rotates in the scene.
• Consider removing a particle emitter from the scene when it is not visible onscreen. Add it just before it becomes visible.