Cloth: Collision improvements

This commit includes several performance, stability, and reliability
improvements to cloth collisions.

Most notably:
* The implementation of a new self-collisions system.
* Multithreading of collision detection.
* Implementation of single sided collisions and normal overrides.
* Replacement of the `plNearestPoints` function from Bullet with a
dedicated solution.

Further, this also includes several bug fixes, and algorithmic
improvements.

Reviewed By: brecht

Differential Revision: http://developer.blender.org/D3712

1 files changed, 23 insertions, 79 deletions

diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp b/source/blender/physics/intern/BPH_mass_spring.cpp
index d94f2094f81..d43ce37cbfe 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -884,20 +884,13 @@ static void cloth_calc_volume_force(ClothModifierData *clmd)
 }
 #endif
 
-/* old collision stuff for cloth, use for continuity
- * until a good replacement is ready
- */
-static void cloth_collision_solve_extra(
-        Depsgraph *depsgraph, Scene *scene, Object *ob, ClothModifierData *clmd, ListBase *effectors,
-        float frame, float step, float dt)
+static void cloth_solve_collisions(Depsgraph *depsgraph, Object *ob, ClothModifierData *clmd, float step, float dt)
 {
 	Cloth *cloth = clmd->clothObject;
 	Implicit_Data *id = cloth->implicit;
 	ClothVertex *verts = cloth->verts;
 	int mvert_num = cloth->mvert_num;
-	const float spf = (float)clmd->sim_parms->stepsPerFrame / clmd->sim_parms->timescale;
-
-	bool do_extra_solve;
+	const float time_multiplier = 1.0f / (clmd->sim_parms->dt * clmd->sim_parms->timescale);
 	int i;
 
 	if (!(clmd->coll_parms->flags & (CLOTH_COLLSETTINGS_FLAG_ENABLED | CLOTH_COLLSETTINGS_FLAG_SELF)))
@@ -906,69 +899,26 @@ static void cloth_collision_solve_extra(
 	if (!clmd->clothObject->bvhtree)
 		return;
 
-	// update verts to current positions
+	BPH_mass_spring_solve_positions(id, dt);
+
+	/* Update verts to current positions. */
 	for (i = 0; i < mvert_num; i++) {
 		BPH_mass_spring_get_new_position(id, i, verts[i].tx);
 
 		sub_v3_v3v3(verts[i].tv, verts[i].tx, verts[i].txold);
-		copy_v3_v3(verts[i].v, verts[i].tv);
-	}
-
-#if 0 /* unused */
-	for (i=0, cv=cloth->verts; i<cloth->mvert_num; i++, cv++) {
-		copy_v3_v3(initial_cos[i], cv->tx);
-	}
-#endif
-
-	// call collision function
-	// TODO: check if "step" or "step+dt" is correct - dg
-	do_extra_solve = cloth_bvh_objcollision(
-	        depsgraph, ob, clmd, step / clmd->sim_parms->timescale, dt / clmd->sim_parms->timescale);
-
-	// copy corrected positions back to simulation
-	for (i = 0; i < mvert_num; i++) {
-		float curx[3];
-		BPH_mass_spring_get_position(id, i, curx);
-		// correct velocity again, just to be sure we had to change it due to adaptive collisions
-		sub_v3_v3v3(verts[i].tv, verts[i].tx, curx);
+		zero_v3(verts[i].dcvel);
 	}
 
-	if (do_extra_solve) {
-//		cloth_calc_helper_forces(ob, clmd, initial_cos, step/clmd->sim_parms->timescale, dt/clmd->sim_parms->timescale);
-
+	if (cloth_bvh_collision(depsgraph, ob, clmd, step / clmd->sim_parms->timescale, dt / clmd->sim_parms->timescale)) {
 		for (i = 0; i < mvert_num; i++) {
-
-			float newv[3];
-
-			if ((clmd->sim_parms->vgroup_mass > 0) && (verts [i].flags & CLOTH_VERT_FLAG_PINNED))
+			if ((clmd->sim_parms->vgroup_mass > 0) && (verts[i].flags & CLOTH_VERT_FLAG_PINNED))
 				continue;
 
-			BPH_mass_spring_set_new_position(id, i, verts[i].tx);
-			mul_v3_v3fl(newv, verts[i].tv, spf);
-			BPH_mass_spring_set_new_velocity(id, i, newv);
+			BPH_mass_spring_get_new_velocity(id, i, verts[i].tv);
+			madd_v3_v3fl(verts[i].tv, verts[i].dcvel, time_multiplier);
+			BPH_mass_spring_set_new_velocity(id, i, verts[i].tv);
 		}
 	}
-
-	// X = Xnew;
-	BPH_mass_spring_apply_result(id);
-
-	if (do_extra_solve) {
-		ImplicitSolverResult result;
-
-		/* initialize forces to zero */
-		BPH_mass_spring_clear_forces(id);
-
-		// calculate forces
-		cloth_calc_force(scene, clmd, frame, effectors, step);
-
-		// calculate new velocity and position
-		BPH_mass_spring_solve_velocities(id, dt, &result);
-//		cloth_record_result(clmd, &result, clmd->sim_parms->stepsPerFrame);
-
-		/* note: positions are advanced only once in the main solver step! */
-
-		BPH_mass_spring_apply_result(id);
-	}
 }
 
 static void cloth_clear_result(ClothModifierData *clmd)
@@ -981,7 +931,7 @@ static void cloth_clear_result(ClothModifierData *clmd)
 	sres->avg_iterations = 0.0f;
 }
 
-static void cloth_record_result(ClothModifierData *clmd, ImplicitSolverResult *result, int steps)
+static void cloth_record_result(ClothModifierData *clmd, ImplicitSolverResult *result, float dt)
 {
 	ClothSolverResult *sres = clmd->solver_result;
 
@@ -990,22 +940,22 @@ static void cloth_record_result(ClothModifierData *clmd, ImplicitSolverResult *r
 		if (result->status == BPH_SOLVER_SUCCESS) {
 			sres->min_error = min_ff(sres->min_error, result->error);
 			sres->max_error = max_ff(sres->max_error, result->error);
-			sres->avg_error += result->error / (float)steps;
+			sres->avg_error += result->error * dt;
 		}
 
 		sres->min_iterations = min_ii(sres->min_iterations, result->iterations);
 		sres->max_iterations = max_ii(sres->max_iterations, result->iterations);
-		sres->avg_iterations += (float)result->iterations / (float)steps;
+		sres->avg_iterations += (float)result->iterations * dt;
 	}
 	else {
 		/* error only makes sense for successful iterations */
 		if (result->status == BPH_SOLVER_SUCCESS) {
 			sres->min_error = sres->max_error = result->error;
-			sres->avg_error += result->error / (float)steps;
+			sres->avg_error += result->error * dt;
 		}
 
 		sres->min_iterations = sres->max_iterations  = result->iterations;
-		sres->avg_iterations += (float)result->iterations / (float)steps;
+		sres->avg_iterations += (float)result->iterations * dt;
 	}
 
 	sres->status |= result->status;
@@ -1025,7 +975,7 @@ int BPH_cloth_solve(Depsgraph *depsgraph, Object *ob, float frame, ClothModifier
 	Cloth *cloth = clmd->clothObject;
 	ClothVertex *verts = cloth->verts/*, *cv*/;
 	unsigned int mvert_num = cloth->mvert_num;
-	float dt = clmd->sim_parms->timescale / clmd->sim_parms->stepsPerFrame;
+	float dt = clmd->sim_parms->dt * clmd->sim_parms->timescale;
 	Implicit_Data *id = cloth->implicit;
 	ColliderContacts *contacts = NULL;
 	int totcolliders = 0;
@@ -1053,12 +1003,6 @@ int BPH_cloth_solve(Depsgraph *depsgraph, Object *ob, float frame, ClothModifier
 	while (step < tf) {
 		ImplicitSolverResult result;
 
-		/* copy velocities for collision */
-		for (i = 0; i < mvert_num; i++) {
-			BPH_mass_spring_get_motion_state(id, i, NULL, verts[i].tv);
-			copy_v3_v3(verts[i].v, verts[i].tv);
-		}
-
 		if (is_hair) {
 			/* determine contact points */
 			if (clmd->coll_parms->flags & CLOTH_COLLSETTINGS_FLAG_ENABLED) {
@@ -1081,18 +1025,18 @@ int BPH_cloth_solve(Depsgraph *depsgraph, Object *ob, float frame, ClothModifier
 
 		// calculate new velocity and position
 		BPH_mass_spring_solve_velocities(id, dt, &result);
-		cloth_record_result(clmd, &result, clmd->sim_parms->stepsPerFrame);
+		cloth_record_result(clmd, &result, dt);
+
+		/* Calculate collision impulses. */
+		if (!is_hair) {
+			cloth_solve_collisions(depsgraph, ob, clmd, step, dt);
+		}
 
 		if (is_hair) {
 			cloth_continuum_step(clmd, dt);
 		}
 
 		BPH_mass_spring_solve_positions(id, dt);
-
-		if (!is_hair) {
-			cloth_collision_solve_extra(depsgraph, scene, ob, clmd, effectors, frame, step, dt);
-		}
-
 		BPH_mass_spring_apply_result(id);
 
 		/* move pinned verts to correct position */