Merge branch 'master' into blender2.8

14 files changed, 334 insertions, 29 deletions

diff --git a/source/blender/blenkernel/BKE_particle.h b/source/blender/blenkernel/BKE_particle.h
index 9492f7e32fa..2db4126057a 100644
--- a/source/blender/blenkernel/BKE_particle.h
+++ b/source/blender/blenkernel/BKE_particle.h
@@ -115,6 +115,7 @@ typedef struct ParticleTexture {
 	float damp, gravity, field;           /* used in physics */
 	float length, clump, kink_freq, kink_amp, effector;  /* used in path caching */
 	float rough1, rough2, roughe;         /* used in path caching */
+	float twist;  /* used in path caching */
 } ParticleTexture;
 
 typedef struct ParticleSeam {
@@ -162,9 +163,11 @@ typedef struct ParticleThreadContext {
 	float *vg_length, *vg_clump, *vg_kink;
 	float *vg_rough1, *vg_rough2, *vg_roughe;
 	float *vg_effector;
+	float *vg_twist;
 
 	struct CurveMapping *clumpcurve;
 	struct CurveMapping *roughcurve;
+	struct CurveMapping *twistcurve;
 } ParticleThreadContext;
 
 typedef struct ParticleTask {
@@ -353,6 +356,7 @@ int psys_get_particle_state(struct ParticleSimulationData *sim, int p, struct Pa
 /* child paths */
 void BKE_particlesettings_clump_curve_init(struct ParticleSettings *part);
 void BKE_particlesettings_rough_curve_init(struct ParticleSettings *part);
+void BKE_particlesettings_twist_curve_init(struct ParticleSettings *part);
 void psys_apply_child_modifiers(struct ParticleThreadContext *ctx, struct ListBase *modifiers,
                                 struct ChildParticle *cpa, struct ParticleTexture *ptex, const float orco[3], const float ornor[3], float hairmat[4][4],
                                 struct ParticleCacheKey *keys, struct ParticleCacheKey *parent_keys, const float parent_orco[3]);
diff --git a/source/blender/blenkernel/intern/particle.c b/source/blender/blenkernel/intern/particle.c
index ef2ed9e2b65..ff70e71edd4 100644
--- a/source/blender/blenkernel/intern/particle.c
+++ b/source/blender/blenkernel/intern/particle.c
@@ -413,6 +413,8 @@ void BKE_particlesettings_free(ParticleSettings *part)
 		curvemapping_free(part->clumpcurve);
 	if (part->roughcurve)
 		curvemapping_free(part->roughcurve);
+	if (part->twistcurve)
+		curvemapping_free(part->twistcurve);
 	
 	free_partdeflect(part->pd);
 	free_partdeflect(part->pd2);
@@ -2144,6 +2146,7 @@ static bool psys_thread_context_init_path(
 	ctx->vg_rough1 = psys_cache_vgroup(ctx->dm, psys, PSYS_VG_ROUGH1);
 	ctx->vg_rough2 = psys_cache_vgroup(ctx->dm, psys, PSYS_VG_ROUGH2);
 	ctx->vg_roughe = psys_cache_vgroup(ctx->dm, psys, PSYS_VG_ROUGHE);
+	ctx->vg_twist = psys_cache_vgroup(ctx->dm, psys, PSYS_VG_TWIST);
 	if (psys->part->flag & PART_CHILD_EFFECT)
 		ctx->vg_effector = psys_cache_vgroup(ctx->dm, psys, PSYS_VG_EFFECTOR);
 
@@ -2162,6 +2165,13 @@ static bool psys_thread_context_init_path(
 	else {
 		ctx->roughcurve = NULL;
 	}
+	if ((part->child_flag & PART_CHILD_USE_TWIST_CURVE) && part->twistcurve) {
+		ctx->twistcurve = curvemapping_copy(part->twistcurve);
+		curvemapping_changed_all(ctx->twistcurve);
+	}
+	else {
+		ctx->twistcurve = NULL;
+	}
 
 	return true;
 }
@@ -2306,7 +2316,19 @@ static void psys_thread_create_path(ParticleTask *task, struct ChildParticle *cp
 
 		/* get the original coordinates (orco) for texture usage */
 		cpa_from = part->from;
-		cpa_num = pa->num;
+
+		/*
+		 * NOTE: Should in theory be the same as:
+		 cpa_num = psys_particle_dm_face_lookup(
+		        ctx->sim.psmd->dm_final,
+		        ctx->sim.psmd->dm_deformed,
+		        pa->num, pa->fuv,
+		        NULL);
+		*/
+		cpa_num = (ELEM(pa->num_dmcache, DMCACHE_ISCHILD, DMCACHE_NOTFOUND))
+		        ? pa->num
+		        : pa->num_dmcache;
+
 		/* XXX hack to avoid messed up particle num and subsequent crash (#40733) */
 		if (cpa_num > ctx->sim.psmd->dm_final->getNumTessFaces(ctx->sim.psmd->dm_final))
 			cpa_num = 0;
@@ -3349,6 +3371,18 @@ void BKE_particlesettings_rough_curve_init(ParticleSettings *part)
 	part->roughcurve = cumap;
 }
 
+void BKE_particlesettings_twist_curve_init(ParticleSettings *part)
+{
+	CurveMapping *cumap = curvemapping_add(1, 0.0f, 0.0f, 1.0f, 1.0f);
+
+	cumap->cm[0].curve[0].x = 0.0f;
+	cumap->cm[0].curve[0].y = 1.0f;
+	cumap->cm[0].curve[1].x = 1.0f;
+	cumap->cm[0].curve[1].y = 1.0f;
+
+	part->twistcurve = cumap;
+}
+
 /**
  * Only copy internal data of ParticleSettings ID from source to already allocated/initialized destination.
  * You probably nerver want to use that directly, use id_copy or BKE_id_copy_ex for typical needs.
@@ -3371,6 +3405,9 @@ void BKE_particlesettings_copy_data(
 	if (part_src->roughcurve) {
 		part_dst->roughcurve = curvemapping_copy(part_src->roughcurve);
 	}
+	if (part_src->twistcurve) {
+		part_dst->twistcurve = curvemapping_copy(part_src->twistcurve);
+	}
 
 	part_dst->boids = boid_copy_settings(part_src->boids);
 
@@ -3490,6 +3527,7 @@ static void get_cpa_texture(DerivedMesh *dm, ParticleSystem *psys, ParticleSetti
 	ptex->ivel = ptex->life = ptex->exist = ptex->size = ptex->damp =
 	ptex->gravity = ptex->field = ptex->time = ptex->clump = ptex->kink_freq = ptex->kink_amp =
 	ptex->effector = ptex->rough1 = ptex->rough2 = ptex->roughe = 1.0f;
+	ptex->twist = 1.0f;
 
 	ptex->length = 1.0f - part->randlength * psys_frand(psys, child_index + 26);
 	ptex->length *= part->clength_thres < psys_frand(psys, child_index + 27) ? part->clength : 1.0f;
@@ -3542,6 +3580,7 @@ static void get_cpa_texture(DerivedMesh *dm, ParticleSystem *psys, ParticleSetti
 			SET_PARTICLE_TEXTURE(PAMAP_KINK_AMP, ptex->kink_amp, mtex->kinkampfac);
 			SET_PARTICLE_TEXTURE(PAMAP_KINK_FREQ, ptex->kink_freq, mtex->kinkfac);
 			SET_PARTICLE_TEXTURE(PAMAP_DENS, ptex->exist, mtex->padensfac);
+			SET_PARTICLE_TEXTURE(PAMAP_TWIST, ptex->twist, mtex->twistfac);
 		}
 	}
 
@@ -3567,6 +3606,7 @@ void psys_get_texture(ParticleSimulationData *sim, ParticleData *pa, ParticleTex
 	ptex->ivel = ptex->life = ptex->exist = ptex->size = ptex->damp =
 	ptex->gravity = ptex->field = ptex->length = ptex->clump = ptex->kink_freq = ptex->kink_amp =
 	ptex->effector = ptex->rough1 = ptex->rough2 = ptex->roughe = 1.0f;
+	ptex->twist = 1.0f;
 
 	ptex->time = (float)(pa - sim->psys->particles) / (float)sim->psys->totpart;
 
@@ -3641,6 +3681,7 @@ void psys_get_texture(ParticleSimulationData *sim, ParticleData *pa, ParticleTex
 			SET_PARTICLE_TEXTURE(PAMAP_GRAVITY, ptex->gravity, mtex->gravityfac);
 			SET_PARTICLE_TEXTURE(PAMAP_DAMP, ptex->damp, mtex->dampfac);
 			SET_PARTICLE_TEXTURE(PAMAP_LENGTH, ptex->length, mtex->lengthfac);
+			SET_PARTICLE_TEXTURE(PAMAP_TWIST, ptex->twist, mtex->twistfac);
 		}
 	}
 
@@ -3732,6 +3773,8 @@ static void get_child_modifier_parameters(ParticleSettings *part, ParticleThread
 		ptex->roughe *= psys_interpolate_value_from_verts(ctx->dm, cpa_from, cpa_num, cpa_fuv, ctx->vg_roughe);
 	if (ctx->vg_effector)
 		ptex->effector *= psys_interpolate_value_from_verts(ctx->dm, cpa_from, cpa_num, cpa_fuv, ctx->vg_effector);
+	if (ctx->vg_twist)
+		ptex->twist *= psys_interpolate_value_from_verts(ctx->dm, cpa_from, cpa_num, cpa_fuv, ctx->vg_twist);
 }
 /* get's hair (or keyed) particles state at the "path time" specified in state->time */
 void psys_get_particle_on_path(ParticleSimulationData *sim, int p, ParticleKey *state, const bool vel)
@@ -3937,7 +3980,18 @@ void psys_get_particle_on_path(ParticleSimulationData *sim, int p, ParticleKey *
 				copy_particle_key(&tstate, state, 1);
 
 			/* apply different deformations to the child path */
-			do_child_modifiers(NULL, sim, &ptex, par->co, par->vel, par->rot, par_orco, cpa, orco, hairmat, state, t);
+			ParticleChildModifierContext modifier_ctx = {NULL};
+			modifier_ctx.thread_ctx = NULL;
+			modifier_ctx.sim = sim;
+			modifier_ctx.ptex = &ptex;
+			modifier_ctx.cpa = cpa;
+			modifier_ctx.orco = orco;
+			modifier_ctx.par_co = par->co;
+			modifier_ctx.par_vel = par->vel;
+			modifier_ctx.par_rot = par->rot;
+			modifier_ctx.par_orco = par_orco;
+			modifier_ctx.parent_keys = psys->childcache ? psys->childcache[p - totpart] : NULL;
+			do_child_modifiers(&modifier_ctx, hairmat, state, t);
 
 			/* try to estimate correct velocity */
 			if (vel) {
@@ -4040,7 +4094,19 @@ int psys_get_particle_state(ParticleSimulationData *sim, int p, ParticleKey *sta
 			CLAMP(t, 0.0f, 1.0f);
 
 			unit_m4(mat);
-			do_child_modifiers(NULL, sim, NULL, key1->co, key1->vel, key1->rot, par_orco, cpa, cpa->fuv, mat, state, t);
+			ParticleChildModifierContext modifier_ctx = {NULL};
+			modifier_ctx.thread_ctx = NULL;
+			modifier_ctx.sim = sim;
+			modifier_ctx.ptex = NULL;
+			modifier_ctx.cpa = cpa;
+			modifier_ctx.orco = cpa->fuv;
+			modifier_ctx.par_co = key1->co;
+			modifier_ctx.par_vel = key1->vel;
+			modifier_ctx.par_rot = key1->rot;
+			modifier_ctx.par_orco = par_orco;
+			modifier_ctx.parent_keys = psys->childcache ? psys->childcache[p - totpart] : NULL;
+
+			do_child_modifiers(&modifier_ctx, mat, state, t);
 
 			if (psys->lattice_deform_data)
 				calc_latt_deform(psys->lattice_deform_data, state->co, psys->lattice_strength);
diff --git a/source/blender/blenkernel/intern/particle_child.c b/source/blender/blenkernel/intern/particle_child.c
index bc4c32f5805..8cdd668b7e7 100644
--- a/source/blender/blenkernel/intern/particle_child.c
+++ b/source/blender/blenkernel/intern/particle_child.c
@@ -235,6 +235,15 @@ static void do_kink_spiral(ParticleThreadContext *ctx, ParticleTexture *ptex, co
 	kink_base[part->kink_axis] = 1.0f;
 	mul_mat3_m4_v3(ctx->sim.ob->obmat, kink_base);
 
+	/* Fill in invariant part of modifier context. */
+	ParticleChildModifierContext modifier_ctx = {NULL};
+	modifier_ctx.thread_ctx = ctx;
+	modifier_ctx.sim = &ctx->sim;
+	modifier_ctx.ptex = ptex;
+	modifier_ctx.cpa = cpa;
+	modifier_ctx.orco = orco;
+	modifier_ctx.parent_keys = parent_keys;
+
 	for (k = 0, key = keys; k < end_index; k++, key++) {
 		float par_time;
 		float *par_co, *par_vel, *par_rot;
@@ -274,8 +283,14 @@ static void do_kink_spiral(ParticleThreadContext *ctx, ParticleTexture *ptex, co
 			do_kink_spiral_deform((ParticleKey *)key, dir, kink, spiral_time, kink_freq, kink_shape, kink_amp, spiral_start);
 		}
 
-		/* apply different deformations to the child path */
-		do_child_modifiers(ctx, &ctx->sim, ptex, par_co, par_vel, par_rot, parent_orco, cpa, orco, hairmat, (ParticleKey *)key, par_time);
+		/* Fill in variant part of modifier context. */
+		modifier_ctx.par_co = par_co;
+		modifier_ctx.par_vel = par_vel;
+		modifier_ctx.par_rot = par_rot;
+		modifier_ctx.par_orco = parent_orco;
+
+		/* Apply different deformations to the child path/ */
+		do_child_modifiers(&modifier_ctx, hairmat, (ParticleKey *)key, par_time);
 	}
 
 	totlen = 0.0f;
@@ -331,19 +346,33 @@ void psys_apply_child_modifiers(ParticleThreadContext *ctx, struct ListBase *mod
 		keys->segments = totkeys - 1;
 	}
 	else {
-		ParticlePathIterator iter;
+		/* Fill in invariant part of modifier context. */
+		ParticleChildModifierContext modifier_ctx = {NULL};
+		modifier_ctx.thread_ctx = ctx;
+		modifier_ctx.sim = &ctx->sim;
+		modifier_ctx.ptex = ptex;
+		modifier_ctx.cpa = cpa;
+		modifier_ctx.orco = orco;
+		modifier_ctx.parent_keys = parent_keys;
 
 		totkeys = ctx->segments + 1;
 		max_length = ptex->length;
 
+		printf("%f\n", ptex->twist);
 		for (k = 0, key = keys; k < totkeys; k++, key++) {
-			ParticleKey *par;
-
+			ParticlePathIterator iter;
 			psys_path_iter_get(&iter, keys, totkeys, parent_keys, k);
-			par = (ParticleKey *)iter.parent_key;
 
-			/* apply different deformations to the child path */
-			do_child_modifiers(ctx, &ctx->sim, ptex, par->co, par->vel, iter.parent_rotation, parent_orco, cpa, orco, hairmat, (ParticleKey *)key, iter.time);
+			ParticleKey *par = (ParticleKey *)iter.parent_key;
+
+			/* Fill in variant part of modifier context. */
+			modifier_ctx.par_co = par->co;
+			modifier_ctx.par_vel = par->vel;
+			modifier_ctx.par_rot = iter.parent_rotation;
+			modifier_ctx.par_orco = parent_orco;
+
+			/* Apply different deformations to the child path. */
+			do_child_modifiers(&modifier_ctx, hairmat, (ParticleKey *)key, iter.time);
 		}
 	}
 
@@ -662,10 +691,100 @@ static void do_rough_curve(const float loc[3], float mat[4][4], float time, floa
 	madd_v3_v3fl(state->co, mat[2], fac * rough[2]);
 }
 
-void do_child_modifiers(ParticleThreadContext *ctx, ParticleSimulationData *sim, ParticleTexture *ptex,
-                        const float par_co[3], const float par_vel[3], const float par_rot[4], const float par_orco[3],
-                        ChildParticle *cpa, const float orco[3], float mat[4][4], ParticleKey *state, float t)
+static int twist_num_segments(const ParticleChildModifierContext *modifier_ctx)
+{
+	ParticleThreadContext *thread_ctx = modifier_ctx->thread_ctx;
+	return (thread_ctx != NULL) ? thread_ctx->segments
+	                            : modifier_ctx->sim->psys->part->draw_step;
+}
+
+static void twist_get_axis(const ParticleChildModifierContext *modifier_ctx,
+                           const float time, float r_axis[3])
+{
+	const int num_segments = twist_num_segments(modifier_ctx);
+	const int index = clamp_i(time * num_segments, 0, num_segments);
+	if (index > 0) {
+		sub_v3_v3v3(r_axis,
+		            modifier_ctx->parent_keys[index].co,
+		            modifier_ctx->parent_keys[index - 1].co);
+	}
+	else {
+		sub_v3_v3v3(r_axis,
+		            modifier_ctx->parent_keys[index + 1].co,
+		            modifier_ctx->parent_keys[index].co);
+	}
+}
+
+static float curvemapping_integrate_clamped(CurveMapping *curve,
+                                            float start, float end, float step)
+{
+	float integral = 0.0f;
+	float x = start;
+	while (x < end) {
+		float y = curvemapping_evaluateF(curve, 0, x);
+		y = clamp_f(y, 0.0f, 1.0f);
+		/* TODO(sergey): Clamp last step to end. */
+		integral += y * step;
+		x += step;
+	}
+	return integral;
+}
+
+static void do_twist(const ParticleChildModifierContext *modifier_ctx,
+                     ParticleKey *state, const float time)
+{
+	ParticleThreadContext *thread_ctx = modifier_ctx->thread_ctx;
+	ParticleSimulationData *sim = modifier_ctx->sim;
+	ParticleTexture *ptex = modifier_ctx->ptex;
+	ParticleSettings *part = sim->psys->part;
+	/* Early output checks. */
+	if (part->childtype != PART_CHILD_PARTICLES) {
+		/* Interpolated children behave weird with twist. */
+		return;
+	}
+	if (part->twist == 0.0f) {
+		/* No twist along the strand.  */
+		return;
+	}
+	/* Dependent on whether it's threaded update or not, curve comes
+	 * from different places.
+	 */
+	CurveMapping *twist_curve = NULL;
+	if (part->child_flag & PART_CHILD_USE_TWIST_CURVE) {
+		twist_curve = (thread_ctx != NULL) ? thread_ctx->twistcurve
+		                                   : part->twistcurve;
+	}
+	/* Axis of rotation. */
+	float axis[3];
+	twist_get_axis(modifier_ctx, time, axis);
+	/* Angle of rotation. */
+	float angle = part->twist;
+	if (ptex != NULL) {
+		angle *= (ptex->twist - 0.5f) * 2.0f;
+	}
+	if (twist_curve != NULL) {
+		const int num_segments = twist_num_segments(modifier_ctx);
+		angle *= curvemapping_integrate_clamped(twist_curve,
+		                                        0.0f, time,
+		                                        1.0f / num_segments);
+	}
+	else {
+		angle *= time;
+	}
+	/* Perform rotation around parent curve. */
+	float vec[3];
+	sub_v3_v3v3(vec, state->co, modifier_ctx->par_co);
+	rotate_v3_v3v3fl(state->co, vec, axis, angle * 2.0f * M_PI);
+	add_v3_v3(state->co, modifier_ctx->par_co);
+}
+
+void do_child_modifiers(const ParticleChildModifierContext *modifier_ctx,
+                        float mat[4][4], ParticleKey *state, float t)
 {
+	ParticleThreadContext *ctx = modifier_ctx->thread_ctx;
+	ParticleSimulationData *sim = modifier_ctx->sim;
+	ParticleTexture *ptex = modifier_ctx->ptex;
+	ChildParticle *cpa = modifier_ctx->cpa;
 	ParticleSettings *part = sim->psys->part;
 	CurveMapping *clumpcurve = NULL, *roughcurve = NULL;
 	int i = cpa - sim->psys->child;
@@ -694,6 +813,8 @@ void do_child_modifiers(ParticleThreadContext *ctx, ParticleSimulationData *sim,
 		rough_end *= ptex->roughe;
 	}
 
+	do_twist(modifier_ctx, state, t);
+
 	if (part->flag & PART_CHILD_EFFECT)
 		/* state is safe to cast, since only co and vel are used */
 		guided = do_guides(sim->eval_ctx, sim->psys->part, sim->psys->effectors, (ParticleKey *)state, cpa->parent, t);
@@ -702,25 +823,43 @@ void do_child_modifiers(ParticleThreadContext *ctx, ParticleSimulationData *sim,
 		float orco_offset[3];
 		float clump;
 
-		sub_v3_v3v3(orco_offset, orco, par_orco);
-		clump = do_clump(state, par_co, t, orco_offset, part->clumpfac, part->clumppow, ptex ? ptex->clump : 1.f,
-		                 part->child_flag & PART_CHILD_USE_CLUMP_NOISE, part->clump_noise_size, clumpcurve);
+		sub_v3_v3v3(orco_offset, modifier_ctx->orco, modifier_ctx->par_orco);
+		clump = do_clump(state,
+		                 modifier_ctx->par_co,
+		                 t,
+		                 orco_offset,
+		                 part->clumpfac,
+		                 part->clumppow,
+		                 ptex ? ptex->clump : 1.0f,
+		                 part->child_flag & PART_CHILD_USE_CLUMP_NOISE,
+		                 part->clump_noise_size,
+		                 clumpcurve);
 
 		if (kink_freq != 0.f) {
 			kink_amp *= (1.f - kink_amp_clump * clump);
 
-			do_kink(state, par_co, par_vel, par_rot, t, kink_freq, part->kink_shape,
-			        kink_amp, part->kink_flat, part->kink, part->kink_axis,
-			        sim->ob->obmat, smooth_start);
+			do_kink(state,
+			        modifier_ctx->par_co,
+			        modifier_ctx->par_vel,
+			        modifier_ctx->par_rot,
+			        t,
+			        kink_freq,
+			        part->kink_shape,
+			        kink_amp,
+			        part->kink_flat,
+			        part->kink,
+			        part->kink_axis,
+			        sim->ob->obmat,
+			        smooth_start);
 		}
 	}
 
 	if (roughcurve) {
-		do_rough_curve(orco, mat, t, rough1, part->rough1_size, roughcurve, state);
+		do_rough_curve(modifier_ctx->orco, mat, t, rough1, part->rough1_size, roughcurve, state);
 	}
 	else {
 		if (rough1 > 0.f)
-			do_rough(orco, mat, t, rough1, part->rough1_size, 0.0, state);
+			do_rough(modifier_ctx->orco, mat, t, rough1, part->rough1_size, 0.0, state);
 
 		if (rough2 > 0.f) {
 			float vec[3];
diff --git a/source/blender/blenkernel/intern/particle_system.c b/source/blender/blenkernel/intern/particle_system.c
index 0fcc918a069..8171f3e7812 100644
--- a/source/blender/blenkernel/intern/particle_system.c
+++ b/source/blender/blenkernel/intern/particle_system.c
@@ -499,6 +499,8 @@ void psys_thread_context_free(ParticleThreadContext *ctx)
 		MEM_freeN(ctx->vg_rough2);
 	if (ctx->vg_roughe)
 		MEM_freeN(ctx->vg_roughe);
+	if (ctx->vg_twist)
+		MEM_freeN(ctx->vg_twist);
 
 	if (ctx->sim.psys->lattice_deform_data) {
 		end_latt_deform(ctx->sim.psys->lattice_deform_data);
@@ -521,6 +523,9 @@ void psys_thread_context_free(ParticleThreadContext *ctx)
 	if (ctx->roughcurve != NULL) {
 		curvemapping_free(ctx->roughcurve);
 	}
+	if (ctx->twistcurve != NULL) {
+		curvemapping_free(ctx->twistcurve);
+	}
 }
 
 static void initialize_particle_texture(ParticleSimulationData *sim, ParticleData *pa, int p)
diff --git a/source/blender/blenkernel/intern/smoke.c b/source/blender/blenkernel/intern/smoke.c
index 9f9818127bc..4ab7b76aaab 100644
--- a/source/blender/blenkernel/intern/smoke.c
+++ b/source/blender/blenkernel/intern/smoke.c
@@ -1287,6 +1287,8 @@ static void emit_from_particles(
 			curvemapping_changed_all(psys->part->clumpcurve);
 		if ((psys->part->child_flag & PART_CHILD_USE_ROUGH_CURVE) && psys->part->roughcurve)
 			curvemapping_changed_all(psys->part->roughcurve);
+		if ((psys->part->child_flag & PART_CHILD_USE_TWIST_CURVE) && psys->part->twistcurve)
+			curvemapping_changed_all(psys->part->twistcurve);
 
 		/* initialize particle cache */
 		if (psys->part->type == PART_HAIR) {
diff --git a/source/blender/blenkernel/intern/texture.c b/source/blender/blenkernel/intern/texture.c
index fcedd880615..71b90641e02 100644
--- a/source/blender/blenkernel/intern/texture.c
+++ b/source/blender/blenkernel/intern/texture.c
@@ -412,6 +412,7 @@ void BKE_texture_mtex_default(MTex *mtex)
 	mtex->kinkfac = 1.0f;
 	mtex->kinkampfac = 1.0f;
 	mtex->roughfac = 1.0f;
+	mtex->twistfac = 1.0f;
 	mtex->padensfac = 1.0f;
 	mtex->lifefac = 1.0f;
 	mtex->sizefac = 1.0f;
diff --git a/source/blender/blenkernel/particle_private.h b/source/blender/blenkernel/particle_private.h
index b4878807df7..2189527118b 100644
--- a/source/blender/blenkernel/particle_private.h
+++ b/source/blender/blenkernel/particle_private.h
@@ -31,12 +31,24 @@
 #ifndef __PARTICLE_PRIVATE_H__
 #define __PARTICLE_PRIVATE_H__
 
+typedef struct ParticleChildModifierContext {
+	ParticleThreadContext *thread_ctx;
+	ParticleSimulationData *sim;
+	ParticleTexture *ptex;
+	ChildParticle *cpa;
+	const float *par_co;    /* float3 */
+	const float *par_vel;   /* float3 */
+	const float *par_rot;   /* float4 */
+	const float *par_orco;  /* float3 */
+	const float *orco;      /* float3 */
+	ParticleCacheKey *parent_keys;
+} ParticleChildModifierContext;
+
 void do_kink(ParticleKey *state, const float par_co[3], const float par_vel[3], const float par_rot[4], float time, float freq, float shape, float amplitude, float flat,
              short type, short axis, float obmat[4][4], int smooth_start);
 float do_clump(ParticleKey *state, const float par_co[3], float time, const float orco_offset[3], float clumpfac, float clumppow, float pa_clump,
                bool use_clump_noise, float clump_noise_size, CurveMapping *clumpcurve);
-void do_child_modifiers(ParticleThreadContext *ctx, ParticleSimulationData *sim,
-                        ParticleTexture *ptex, const float par_co[3], const float par_vel[3], const float par_rot[4], const float par_orco[3],
-                        ChildParticle *cpa, const float orco[3], float mat[4][4], ParticleKey *state, float t);
+void do_child_modifiers(const ParticleChildModifierContext *modifier_ctx,
+                        float mat[4][4], ParticleKey *state, float t);
 
 #endif /* __PARTICLE_PRIVATE_H__ */
diff --git a/source/blender/blenlib/intern/math_vector.c b/source/blender/blenlib/intern/math_vector.c
index 05562502278..d6e48fa59e7 100644
--- a/source/blender/blenlib/intern/math_vector.c
+++ b/source/blender/blenlib/intern/math_vector.c
@@ -890,6 +890,8 @@ void rotate_normalized_v3_v3v3fl(float out[3], const float p[3], const float axi
 
 void rotate_v3_v3v3fl(float r[3], const float p[3], const float axis[3], const float angle)
 {
+	BLI_assert(r != p);
+
 	float axis_n[3];
 
 	normalize_v3_v3(axis_n, axis);
diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index b75a2de935a..c20246bcbfb 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -4406,6 +4406,9 @@ static void direct_link_particlesettings(FileData *fd, ParticleSettings *part)
 	part->roughcurve = newdataadr(fd, part->roughcurve);
 	if (part->roughcurve)
 		direct_link_curvemapping(fd, part->roughcurve);
+	part->twistcurve = newdataadr(fd, part->twistcurve);
+	if (part->twistcurve)
+		direct_link_curvemapping(fd, part->twistcurve);
 
 	part->effector_weights = newdataadr(fd, part->effector_weights);
 	if (!part->effector_weights)
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index 712ce334002..d566058f4a7 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -1337,6 +1337,9 @@ static void write_particlesettings(WriteData *wd, ParticleSettings *part)
 		if (part->roughcurve) {
 			write_curvemapping(wd, part->roughcurve);
 		}
+		if (part->twistcurve) {
+			write_curvemapping(wd, part->twistcurve);
+		}
 
 		for (ParticleDupliWeight *dw = part->dupliweights.first; dw; dw = dw->next) {
 			/* update indices, but only if dw->ob is set (can be NULL after loading e.g.) */
diff --git a/source/blender/editors/space_view3d/drawobject.c b/source/blender/editors/space_view3d/drawobject.c
index 240eda4bf8e..75c217c4f0c 100644
--- a/source/blender/editors/space_view3d/drawobject.c
+++ b/source/blender/editors/space_view3d/drawobject.c
@@ -5978,6 +5978,8 @@ static void draw_new_particle_system(
 		curvemapping_changed_all(psys->part->clumpcurve);
 	if ((psys->part->child_flag & PART_CHILD_USE_ROUGH_CURVE) && psys->part->roughcurve)
 		curvemapping_changed_all(psys->part->roughcurve);
+	if ((psys->part->child_flag & PART_CHILD_USE_TWIST_CURVE) && psys->part->twistcurve)
+		curvemapping_changed_all(psys->part->twistcurve);
 
 /* 2. */
 	sim.eval_ctx = eval_ctx;
diff --git a/source/blender/makesdna/DNA_particle_types.h b/source/blender/makesdna/DNA_particle_types.h
index ea7905eb2ad..a7be2e37c4b 100644
--- a/source/blender/makesdna/DNA_particle_types.h
+++ b/source/blender/makesdna/DNA_particle_types.h
@@ -263,6 +263,11 @@ typedef struct ParticleSettings {
 
 	short pad5;
 	int recalc;
+
+	float twist;
+	float pad6;
+	struct CurveMapping *twistcurve;
+	void *pad7;
 } ParticleSettings;
 
 typedef struct ParticleSystem {
@@ -305,7 +310,8 @@ typedef struct ParticleSystem {
 	char bb_uvname[3][64];					/* billboard uv name, MAX_CUSTOMDATA_LAYER_NAME */
 
 	/* if you change these remember to update array lengths to PSYS_TOT_VG! */
-	short vgroup[12], vg_neg, rt3;			/* vertex groups, 0==disable, 1==starting index */
+	short vgroup[13], vg_neg, rt3;			/* vertex groups, 0==disable, 1==starting index */
+	char pad[6];
 
 	/* temporary storage during render */
 	struct ParticleRenderData *renderdata;
@@ -439,6 +445,7 @@ typedef enum eParticleChildFlag {
 	PART_CHILD_USE_CLUMP_NOISE  = (1<<0),
 	PART_CHILD_USE_CLUMP_CURVE  = (1<<1),
 	PART_CHILD_USE_ROUGH_CURVE  = (1<<2),
+	PART_CHILD_USE_TWIST_CURVE  = (1<<3),
 } eParticleChildFlag;
 
 /* part->draw_col */
@@ -566,7 +573,7 @@ typedef enum eParticleChildFlag {
 #define PART_DUPLIW_CURRENT	1
 
 /* psys->vg */
-#define PSYS_TOT_VG			12
+#define PSYS_TOT_VG			13
 
 #define PSYS_VG_DENSITY		0
 #define PSYS_VG_VEL			1
@@ -580,6 +587,7 @@ typedef enum eParticleChildFlag {
 #define PSYS_VG_TAN			9
 #define PSYS_VG_ROT			10
 #define PSYS_VG_EFFECTOR	11
+#define PSYS_VG_TWIST	12
 
 /* ParticleTarget->flag */
 #define PTARGET_CURRENT		1
@@ -611,7 +619,8 @@ typedef enum eParticleTextureInfluence {
 	PAMAP_KINK_AMP	= (1<<12),
 	PAMAP_ROUGH		= (1<<9),
 	PAMAP_LENGTH	= (1<<4),
-	PAMAP_CHILD		= (PAMAP_CLUMP | PAMAP_KINK_FREQ | PAMAP_KINK_AMP | PAMAP_ROUGH | PAMAP_LENGTH),
+	PAMAP_TWIST	= (1<<13),
+	PAMAP_CHILD		= (PAMAP_CLUMP | PAMAP_KINK_FREQ | PAMAP_KINK_AMP | PAMAP_ROUGH | PAMAP_LENGTH | PAMAP_TWIST),
 } eParticleTextureInfluence;
 
 #endif
diff --git a/source/blender/makesdna/DNA_texture_types.h b/source/blender/makesdna/DNA_texture_types.h
index 995d7645dc0..0eb54a9b5b3 100644
--- a/source/blender/makesdna/DNA_texture_types.h
+++ b/source/blender/makesdna/DNA_texture_types.h
@@ -86,7 +86,7 @@ typedef struct MTex {
 	float timefac, lengthfac, clumpfac, dampfac;
 	float kinkfac, kinkampfac, roughfac, padensfac, gravityfac;
 	float lifefac, sizefac, ivelfac, fieldfac;
-	int pad2;
+	float twistfac;
 
 	/* lamp */
 	float shadowfac;
diff --git a/source/blender/makesrna/intern/rna_particle.c b/source/blender/makesrna/intern/rna_particle.c
index 1a819c3bcdb..14bf612f467 100644
--- a/source/blender/makesrna/intern/rna_particle.c
+++ b/source/blender/makesrna/intern/rna_particle.c
@@ -953,6 +953,19 @@ static void rna_ParticleSettings_use_roughness_curve_update(Main *bmain, Scene *
 	rna_Particle_redo_child(bmain, scene, ptr);
 }
 
+static void rna_ParticleSettings_use_twist_curve_update(Main *bmain, Scene *scene, PointerRNA *ptr)
+{
+	ParticleSettings *part = ptr->data;
+
+	if (part->child_flag & PART_CHILD_USE_TWIST_CURVE) {
+		if (!part->twistcurve) {
+			BKE_particlesettings_twist_curve_init(part);
+		}
+	}
+
+	rna_Particle_redo_child(bmain, scene, ptr);
+}
+
 static void rna_ParticleSystem_name_set(PointerRNA *ptr, const char *value)
 {
 	Object *ob = ptr->id.data;
@@ -1309,6 +1322,7 @@ static void rna_ParticleVGroup_name_get_8(PointerRNA *ptr, char *value) { psys_v
 static void rna_ParticleVGroup_name_get_9(PointerRNA *ptr, char *value) { psys_vg_name_get__internal(ptr, value, 9); }
 static void rna_ParticleVGroup_name_get_10(PointerRNA *ptr, char *value) { psys_vg_name_get__internal(ptr, value, 10); }
 static void rna_ParticleVGroup_name_get_11(PointerRNA *ptr, char *value) { psys_vg_name_get__internal(ptr, value, 11); }
+static void rna_ParticleVGroup_name_get_12(PointerRNA *ptr, char *value) { psys_vg_name_get__internal(ptr, value, 12); }
 
 static int rna_ParticleVGroup_name_len_0(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 0); }
 static int rna_ParticleVGroup_name_len_1(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 1); }
@@ -1322,6 +1336,7 @@ static int rna_ParticleVGroup_name_len_8(PointerRNA *ptr) { return psys_vg_name_
 static int rna_ParticleVGroup_name_len_9(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 9); }
 static int rna_ParticleVGroup_name_len_10(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 10); }
 static int rna_ParticleVGroup_name_len_11(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 11); }
+static int rna_ParticleVGroup_name_len_12(PointerRNA *ptr) { return psys_vg_name_len__internal(ptr, 12); }
 
 static void rna_ParticleVGroup_name_set_0(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 0); }
 static void rna_ParticleVGroup_name_set_1(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 1); }
@@ -1335,6 +1350,7 @@ static void rna_ParticleVGroup_name_set_8(PointerRNA *ptr, const char *value) {
 static void rna_ParticleVGroup_name_set_9(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 9); }
 static void rna_ParticleVGroup_name_set_10(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 10); }
 static void rna_ParticleVGroup_name_set_11(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 11); }
+static void rna_ParticleVGroup_name_set_12(PointerRNA *ptr, const char *value) { psys_vg_name_set__internal(ptr, value, 12); }
 
 
 #else
@@ -1887,6 +1903,10 @@ static void rna_def_particle_settings_mtex(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Length", "Affect the child hair length");
 	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
 
+	prop = RNA_def_property(srna, "use_map_twist", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "mapto", PAMAP_TWIST);
+	RNA_def_property_ui_text(prop, "Twist", "Affect the child twist");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
 
 	/* influence factors */
 	prop = RNA_def_property(srna, "time_factor", PROP_FLOAT, PROP_NONE);
@@ -1968,6 +1988,12 @@ static void rna_def_particle_settings_mtex(BlenderRNA *brna)
 	RNA_def_property_ui_range(prop, 0, 1, 10, 3);
 	RNA_def_property_ui_text(prop, "Rough Factor", "Amount texture affects child roughness");
 	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
+
+	prop = RNA_def_property(srna, "twist_factor", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_float_sdna(prop, NULL, "twistfac");
+	RNA_def_property_ui_range(prop, 0, 1, 10, 3);
+	RNA_def_property_ui_text(prop, "Twist Factor", "Amount texture affects child twist");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
 }
 
 static void rna_def_particle_settings(BlenderRNA *brna)
@@ -3174,6 +3200,25 @@ static void rna_def_particle_settings(BlenderRNA *brna)
 	RNA_def_property_struct_type(prop, "FieldSettings");
 	RNA_def_property_pointer_funcs(prop, "rna_Particle_field2_get", NULL, NULL, NULL);
 	RNA_def_property_ui_text(prop, "Force Field 2", "");
+
+	/* twist */
+	prop = RNA_def_property(srna, "twist", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_range(prop, -100000.0f, 100000.0f);
+	RNA_def_property_ui_range(prop, -10.0f, 10.0f, 0.1, 3);
+	RNA_def_property_ui_text(prop, "Twist", "Number of turns around parent allong the strand");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
+
+	prop = RNA_def_property(srna, "use_twist_curve", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "child_flag", PART_CHILD_USE_TWIST_CURVE);
+	RNA_def_property_ui_text(prop, "Use Twist Curve", "Use a curve to define twist");
+	RNA_def_property_update(prop, 0, "rna_ParticleSettings_use_twist_curve_update");
+
+	prop = RNA_def_property(srna, "twist_curve", PROP_POINTER, PROP_NONE);
+	RNA_def_property_pointer_sdna(prop, NULL, "twistcurve");
+	RNA_def_property_struct_type(prop, "CurveMapping");
+	RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+	RNA_def_property_ui_text(prop, "Twist Curve", "Curve defining twist");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
 }
 
 static void rna_def_particle_target(BlenderRNA *brna)
@@ -3507,6 +3552,18 @@ static void rna_def_particle_system(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Vertex Group Field Negate", "Negate the effect of the field vertex group");
 	RNA_def_property_update(prop, 0, "rna_Particle_reset");
 
+	prop = RNA_def_property(srna, "vertex_group_twist", PROP_STRING, PROP_NONE);
+	RNA_def_property_string_funcs(prop, "rna_ParticleVGroup_name_get_12", "rna_ParticleVGroup_name_len_12",
+	                              "rna_ParticleVGroup_name_set_12");
+	RNA_def_property_ui_text(prop, "Vertex Group Twist", "Vertex group to control twist");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
+
+	prop = RNA_def_property(srna, "invert_vertex_group_twist", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "vg_neg", (1 << PSYS_VG_TWIST));
+	RNA_def_property_ui_text(prop, "Vertex Group Twist Negate",
+	                         "Negate the effect of the twist vertex group");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo_child");
+
 	/* pointcache */
 	prop = RNA_def_property(srna, "point_cache", PROP_POINTER, PROP_NONE);
 	RNA_def_property_flag(prop, PROP_NEVER_NULL);