handle(_:forProperties:handler:)
Adds a block that modifies particle properties, to be executed at a specified event in the lifetimes of particles in the system.
Declaration
func handle(_ event: SCNParticleEvent, forProperties properties: [SCNParticleSystem.ParticleProperty], handler block: @escaping SCNParticleEventBlock)Parameters
- event:
The event at which to call the block. See Scnparticleevent for allowed values.
- properties:
An array containing one or more of the constants listed in
Particle Property Keys, each of which specifies a property of the appearance or behaviors of particles in the particle system. - block:
A Scnparticleeventblock block to be called every time SceneKit renders a frame. In this block you can modify the properties of particles in the system.
Discussion
By associating a block with one or more particle properties, you can run arbitrary code that modifies those properties when a significant event in the particle simulation occurs for one or more particles. For example, you can use the following code with a confetti effect to randomly switch between two distinct colors for each spawned particle:
[system handleEvent:SCNParticleEventBirth
forProperties:@[SCNParticlePropertyColor]
withBlock:^(void **data, size_t *dataStride, uint32_t *indices , NSInteger count) {
for (NSInteger i = 0; i < count; ++i) {
float *color = (float *)((char *)data[0] + dataStride[0] * i);
if (rand() & 0x1) { // Switch the green and red color components.
color[0] = color[1];
color[1] = 0;
}
}
}];