Use o framework Accelerate para cálculos vetorizados e manter o framerate alto. Com o layout Structure of Arrays (SoA), o acesso à memória é contíguo, tornando os cálculos gravitacionais muito mais eficientes.
func updatePhysics(dt: Float, earthMass: Float, killRadiusSq: Float, maxRadiusSq: Float) {
guard activeCount > 0 else { return }
let count = activeCount
let n = vDSP_Length(count)
withSixBuffers(&posX, &posY, &posZ, &velX, &velY, &velZ) { pX, pY, pZ, vX, vY, vZ in
let xBase = pX.baseAddress!
let yBase = pY.baseAddress!
let zBase = pZ.baseAddress!
let vxBase = vX.baseAddress!
let vyBase = vY.baseAddress!
let vzBase = vZ.baseAddress!
// distSq = posX² + posY² + posZ²
vDSP_vsq(xBase, 1, scratchA, 1, n)
vDSP_vsq(yBase, 1, scratchC, 1, n)
vDSP_vadd(scratchA, 1, scratchC, 1, scratchA, 1, n)
vDSP_vsq(zBase, 1, scratchC, 1, n)
vDSP_vadd(scratchA, 1, scratchC, 1, scratchA, 1, n)
// invDist = rsqrt(distSq)
var n32 = Int32(count)
vvrsqrtf(scratchB, scratchA, &n32)
// factor = -earthMass * dt * invDist³
vDSP_vmul(scratchB, 1, scratchB, 1, scratchC, 1, n)
vDSP_vmul(scratchC, 1, scratchB, 1, scratchC, 1, n)
var coeff = -earthMass * dt
vDSP_vsmul(scratchC, 1, &coeff, scratchC, 1, n)
// Mask out-of-range particles
for i in 0..<count {
if scratchA[i] < killRadiusSq || scratchA[i] > maxRadiusSq {
scratchC[i] = 0
}
}
// vel += pos * factor
vDSP_vma(xBase, 1, scratchC, 1, vxBase, 1, vxBase, 1, n)
vDSP_vma(yBase, 1, scratchC, 1, vyBase, 1, vyBase, 1, n)
vDSP_vma(zBase, 1, scratchC, 1, vzBase, 1, vzBase, 1, n)
// pos += vel * dt
var dt_val = dt
vDSP_vsma(vxBase, 1, &dt_val, xBase, 1, xBase, 1, n)
vDSP_vsma(vyBase, 1, &dt_val, yBase, 1, yBase, 1, n)
vDSP_vsma(vzBase, 1, &dt_val, zBase, 1, zBase, 1, n)
}
}