Viscoelastic springs for sph particle fluids, original patch by Stephen Whitehorn (chickencoop)

* Viscoelastic springs between the fluid particles can simulate all kinds
  of viscous and elastic substances, such as jelly and honey. This is
  achieved by creating springs dynamically between neighboring particles
  and adjusting their rest length based on stretching/compression.
* This nearly completes the currently intended functionality for particle
  fluids. The last missing thing is a surfacing extraction algorithm,
  which is needed for a proper representation of a sph fluid.
* I also cleaned up and renamed some of the fluid parameters to make the
  ui a bit easier to understand.
* One addition to the patch is an option to use "initial rest length" for
  the springs, which uses the lengths between the particles at the time of
  spring creation as the spring rest lengths instead of interaction radius/2.
  This makes the fluid keep it's original shape better (good for very
  viscoelastic materials), but can create large density differences inside
  the fluid (not really physically correct for a fluid).
* Viscoelastic springs are stored in point cache as extra data.

1 files changed, 58 insertions, 12 deletions

diff --git a/source/blender/blenkernel/intern/pointcache.c b/source/blender/blenkernel/intern/pointcache.c
index eb0601b413e..5408e57f10d 100644
--- a/source/blender/blenkernel/intern/pointcache.c
+++ b/source/blender/blenkernel/intern/pointcache.c
@@ -390,6 +390,48 @@ static int  ptcache_particle_totwrite(void *psys_v, int cfra)
 	return totwrite;
 }
 
+static void ptcache_particle_extra_write(void *psys_v, PTCacheMem *pm, int UNUSED(cfra))
+{
+	ParticleSystem *psys = psys_v;
+	PTCacheExtra *extra = NULL;
+
+	if(psys->part->phystype == PART_PHYS_FLUID &&
+		psys->part->fluid && psys->part->fluid->flag & SPH_VISCOELASTIC_SPRINGS &&
+		psys->tot_fluidsprings && psys->fluid_springs) {
+
+		extra = MEM_callocN(sizeof(PTCacheExtra), "Point cache: fluid extra data");
+
+		extra->type = BPHYS_EXTRA_FLUID_SPRINGS;
+		extra->totdata = psys->tot_fluidsprings;
+
+		extra->data = MEM_callocN(extra->totdata * ptcache_extra_datasize[extra->type], "Point cache: extra data");
+		memcpy(extra->data, psys->fluid_springs, extra->totdata * ptcache_extra_datasize[extra->type]);
+
+		BLI_addtail(&pm->extradata, extra);
+	}
+}
+
+static int ptcache_particle_extra_read(void *psys_v, PTCacheMem *pm, float UNUSED(cfra))
+{
+	ParticleSystem *psys = psys_v;
+	PTCacheExtra *extra = pm->extradata.first;
+
+	for(; extra; extra=extra->next) {
+		switch(extra->type) {
+			case BPHYS_EXTRA_FLUID_SPRINGS:
+			{
+				if(psys->fluid_springs)
+					MEM_freeN(psys->fluid_springs);
+
+				psys->fluid_springs = MEM_dupallocN(extra->data);
+				psys->tot_fluidsprings = psys->alloc_fluidsprings = extra->totdata;
+				break;
+			}
+		}
+	}
+	return 1;
+}
+
 /* Cloth functions */
 static int  ptcache_cloth_write(int index, void *cloth_v, void **data, int UNUSED(cfra))
 {
@@ -667,6 +709,10 @@ void BKE_ptcache_id_from_particles(PTCacheID *pid, Object *ob, ParticleSystem *p
 
 	if(psys->part->phystype == PART_PHYS_BOIDS)
 		pid->data_types|= (1<<BPHYS_DATA_AVELOCITY) | (1<<BPHYS_DATA_ROTATION) | (1<<BPHYS_DATA_BOIDS);
+	else if(psys->part->phystype == PART_PHYS_FLUID && psys->part->fluid && psys->part->fluid->flag & SPH_VISCOELASTIC_SPRINGS) {
+		pid->write_extra_data = ptcache_particle_extra_write;
+		pid->read_extra_data = ptcache_particle_extra_read;
+	}
 
 	if(psys->part->rotmode!=PART_ROT_VEL
 		|| psys->part->avemode!=PART_AVE_SPIN || psys->part->avefac!=0.0f)
@@ -1261,9 +1307,13 @@ static void ptcache_extra_free(PTCacheMem *pm)
 {
 	PTCacheExtra *extra = pm->extradata.first;
 
-	for(; extra; extra=extra->next) {
-		if(extra->data)
-			MEM_freeN(extra->data);
+	if(extra) {
+		for(; extra; extra=extra->next) {
+			if(extra->data)
+				MEM_freeN(extra->data);
+		}
+
+		BLI_freelistN(&pm->extradata);
 	}
 }
 static int ptcache_old_elemsize(PTCacheID *pid)
@@ -1383,16 +1433,14 @@ static PTCacheMem *ptcache_disk_frame_to_mem(PTCacheID *pid, int cfra)
 
 			extra->type = extratype;
 
-			ptcache_file_read(pf, &extra->flag, 1, sizeof(unsigned int));
 			ptcache_file_read(pf, &extra->totdata, 1, sizeof(unsigned int));
-			ptcache_file_read(pf, &extra->datasize, 1, sizeof(unsigned int));
 
-			extra->data = MEM_callocN(extra->totdata * extra->datasize, "Pointcache extradata->data");
+			extra->data = MEM_callocN(extra->totdata * ptcache_extra_datasize[extra->type], "Pointcache extradata->data");
 
 			if(pf->flag & PTCACHE_TYPEFLAG_COMPRESS)
-				ptcache_file_compressed_read(pf, (unsigned char*)(extra->data), extra->totdata*extra->datasize);
+				ptcache_file_compressed_read(pf, (unsigned char*)(extra->data), extra->totdata*ptcache_extra_datasize[extra->type]);
 			else
-				ptcache_file_read(pf, extra->data, extra->totdata, extra->datasize);
+				ptcache_file_read(pf, extra->data, extra->totdata, ptcache_extra_datasize[extra->type]);
 
 			BLI_addtail(&pm->extradata, extra);
 		}
@@ -1475,18 +1523,16 @@ static int ptcache_mem_frame_to_disk(PTCacheID *pid, PTCacheMem *pm)
 				continue;
 
 			ptcache_file_write(pf, &extra->type, 1, sizeof(unsigned int));
-			ptcache_file_write(pf, &extra->flag, 1, sizeof(unsigned int));
 			ptcache_file_write(pf, &extra->totdata, 1, sizeof(unsigned int));
-			ptcache_file_write(pf, &extra->datasize, 1, sizeof(unsigned int));
 
 			if(pid->cache->compression) {
-				unsigned int in_len = extra->totdata * extra->datasize;
+				unsigned int in_len = extra->totdata * ptcache_extra_datasize[extra->type];
 				unsigned char *out = (unsigned char *)MEM_callocN(LZO_OUT_LEN(in_len)*4, "pointcache_lzo_buffer");
 				ptcache_file_compressed_write(pf, (unsigned char*)(extra->data), in_len, out, pid->cache->compression);
 				MEM_freeN(out);
 			}
 			else {
-				ptcache_file_write(pf, extra->data, extra->totdata, extra->datasize);
+				ptcache_file_write(pf, extra->data, extra->totdata, ptcache_extra_datasize[extra->type]);
 			}
 		}
 	}