Fix T35247: Particle texture behaves incorrectly after changing the number of particles

Root of the issue goes to the order of particle initialization which does
texture evaluation (which does depend on particle coordinate) and particle
birth coordinate calculation. So basically what happened is:

* Changing number of particles re-allocated all the particles,
  which sets their coordinate to (0,0,0)
* Texture evaluation used this non-initialized coordinate
* Coordinates were calculated for particles

Reshuffled code a bit so now texture evaluation happens after particles.
coordinate calculation. Basically moved texture evaluation to particle
reset function. Reset happens after initialization anyway and it does
know particle coordinates. Also, if reset is being called without init
then it's also kind of logical to re-evaluate texture because particle
coordinates might change.

1 files changed, 16 insertions, 6 deletions

diff --git a/source/blender/blenkernel/intern/particle_system.c b/source/blender/blenkernel/intern/particle_system.c
index 78db7e67b23..6ae3e2e9d5e 100644
--- a/source/blender/blenkernel/intern/particle_system.c
+++ b/source/blender/blenkernel/intern/particle_system.c
@@ -1540,23 +1540,26 @@ void psys_threads_free(ParticleThread *threads)
 	MEM_freeN(threads);
 }
 
-/* set particle parameters that don't change during particle's life */
-void initialize_particle(ParticleSimulationData *sim, ParticleData *pa, int p)
+static void initialize_particle_texture(ParticleSimulationData *sim, ParticleData *pa, int p)
 {
 	ParticleSystem *psys = sim->psys;
 	ParticleSettings *part = psys->part;
 	ParticleTexture ptex;
 
-	pa->flag &= ~PARS_UNEXIST;
-
 	if (part->type != PART_FLUID) {
 		psys_get_texture(sim, pa, &ptex, PAMAP_INIT, 0.f);
-		
+
 		if (ptex.exist < PSYS_FRAND(p+125))
 			pa->flag |= PARS_UNEXIST;
 
 		pa->time = (part->type == PART_HAIR) ? 0.f : part->sta + (part->end - part->sta)*ptex.time;
 	}
+}
+
+/* set particle parameters that don't change during particle's life */
+void initialize_particle(ParticleData *pa)
+{
+	pa->flag &= ~PARS_UNEXIST;
 
 	pa->hair_index = 0;
 	/* we can't reset to -1 anymore since we've figured out correct index in distribute_particles */
@@ -1572,7 +1575,7 @@ static void initialize_all_particles(ParticleSimulationData *sim)
 
 	LOOP_PARTICLES {
 		if ((pa->flag & PARS_UNEXIST)==0)
-			initialize_particle(sim, pa, p);
+			initialize_particle(pa);
 
 		if (pa->flag & PARS_UNEXIST)
 			psys->totunexist++;
@@ -1984,6 +1987,13 @@ void reset_particle(ParticleSimulationData *sim, ParticleData *pa, float dtime,
 
 	psys_get_birth_coordinates(sim, pa, &pa->state, dtime, cfra);
 
+	/* Initialize particle settings which depends on texture.
+	 *
+	 * We could only do it now because we'll need to know coordinate
+	 * before sampling the texture.
+	 */
+	initialize_particle_texture(sim, pa, p);
+
 	if (part->phystype==PART_PHYS_BOIDS && pa->boid) {
 		BoidParticle *bpa = pa->boid;