SCNParticleModifierBlock
The signature for blocks called by SceneKit to modify particle properties on each frame of simulation, used by the Addmodifier(forproperties:at:modifier:) method.
Declaration
typealias SCNParticleModifierBlock = (UnsafeMutablePointer<UnsafeMutableRawPointer>, UnsafeMutablePointer<Int>, Int, Int, Float) -> VoidDiscussion
The block takes the following parameters:
- data
An array of floating-point values containing stripes of property data for the system’s particles. The width and format of each data stripe depend on the properties you specify when calling the addModifier(forProperties:at:modifier:) method.
- dataStride
An array identifying the offset, in bytes, of each property’s value in the data stripe for each particle. The order of offsets in this array corresponds to the order of the
propertiesarray you specify when calling the addModifier(forProperties:at:modifier:) method.- start
The index of the first particle’s data stripe in the
dataarray.- end
The index of the last particle’s data stripe in the
dataarray.- deltaTime
The elapsed time, in seconds, since the last frame of simulation.
Use this block to change properties of individual particles on each frame of simulation.
The following example illustrates setting up a modifier block that alters particle’s position and velocity:
[system addModifierForProperties:@[SCNParticlePropertyPosition,
SCNParticlePropertyVelocity]
atStage:SCNParticleModifierStagePostDynamics
withBlock:^(void **data, size_t *dataStride, NSInteger start, NSInteger end, float deltaTime) {
// For each particle to be processed,
// calculate pointers in the data to each property's value:
for (NSInteger i = start; i < end; ++i) {
// SCNParticlePropertyPosition (float3)
float *pos = (float *)((char *)data[0] + dataStride[0] * i);
// pos[0..2] are the xyz components of the particle's position.
// SCNParticlePropertyVelocity (float3)
float *vel = (float *)((char *)data[1] + dataStride[1] * i);
// vel[0..2] are the xyz components of the particle's position.
// Now, compute a new position and velocity (not shown).
}
}];