Cloth Simulation: add time scale property

This setting can also be animated, to create a "time warp" effect.

D2122 by @LucaRood

release/scripts/startup/bl_ui/properties_physics_cloth.py

@@ -75,6 +75,11 @@ class PHYSICS_PT_cloth(PhysicButtonsPanel, Panel):
         split.label(text="Quality:")
         split.prop(cloth, "quality", text="Steps")
 
+        split = layout.split(percentage=0.25)
+
+        split.label(text="Speed:")
+        split.prop(cloth, "time_scale", text="Multiplier")
+
         split = layout.split()
 
         col = split.column()

source/blender/blenkernel/intern/cloth.c

@@ -97,6 +97,7 @@ void cloth_init(ClothModifierData *clmd )
 	clmd->sim_parms->avg_spring_len = 0.0;
 	clmd->sim_parms->presets = 2; /* cotton as start setting */
 	clmd->sim_parms->timescale = 1.0f; /* speed factor, describes how fast cloth moves */
+	clmd->sim_parms->time_scale = 1.0f; /* multiplies cloth speed */
 	clmd->sim_parms->reset = 0;
 	clmd->sim_parms->vel_damping = 1.0f; /* 1.0 = no damping, 0.0 = fully dampened */
 	
@@ -411,7 +412,7 @@ void clothModifier_do(ClothModifierData *clmd, Scene *scene, Object *ob, Derived
 
 	BKE_ptcache_id_from_cloth(&pid, ob, clmd);
 	BKE_ptcache_id_time(&pid, scene, framenr, &startframe, &endframe, &timescale);
-	clmd->sim_parms->timescale= timescale;
+	clmd->sim_parms->timescale= timescale * clmd->sim_parms->time_scale;
 
 	if (clmd->sim_parms->reset || (clmd->clothObject && dm->getNumVerts(dm) != clmd->clothObject->mvert_num)) {
 		clmd->sim_parms->reset = 0;

source/blender/blenloader/intern/versioning_270.c

@@ -1231,5 +1231,24 @@ void blo_do_versions_270(FileData *fd, Library *UNUSED(lib), Main *main)
 				br->flag |= BRUSH_ACCUMULATE;
 			}
 		}
+
+		if (!DNA_struct_elem_find(fd->filesdna, "ClothSimSettings", "float", "time_scale")) {
+			Object *ob;
+			ModifierData *md;
+			for (ob = main->object.first; ob; ob = ob->id.next) {
+				for (md = ob->modifiers.first; md; md = md->next) {
+					if (md->type == eModifierType_Cloth) {
+						ClothModifierData *clmd = (ClothModifierData *)md;
+						clmd->sim_parms->time_scale = 1.0f;
+					}
+					else if (md->type == eModifierType_ParticleSystem) {
+						ParticleSystemModifierData *pmd = (ParticleSystemModifierData *)md;
+						if (pmd->psys->clmd) {
+							pmd->psys->clmd->sim_parms->time_scale = 1.0f;
+						}
+					}
+				}
+			}
+		}
 	}
 }

source/blender/makesdna/DNA_cloth_types.h

@@ -63,6 +63,7 @@ typedef struct ClothSimSettings {
 	float	max_sewing; 	/* max sewing force */
 	float 	avg_spring_len; /* used for normalized springs */
 	float 	timescale; /* parameter how fast cloth runs */
+	float	time_scale; /* multiplies cloth speed */
 	float	maxgoal; 	/* see SB */
 	float	eff_force_scale;/* Scaling of effector forces (see softbody_calc_forces).*/
 	float	eff_wind_scale;	/* Scaling of effector wind (see softbody_calc_forces).	*/
@@ -98,6 +99,7 @@ typedef struct ClothSimSettings {
 	short	presets; /* used for presets on GUI */
 	short 	reset;
 
+	char pad0[4];
 	struct EffectorWeights *effector_weights;
 } ClothSimSettings;
 

source/blender/makesrna/intern/rna_cloth.c

@@ -442,6 +442,13 @@ static void rna_def_cloth_sim_settings(BlenderRNA *brna)
 	                         "Quality of the simulation in steps per frame (higher is better quality but slower)");
 	RNA_def_property_update(prop, 0, "rna_cloth_update");
 
+	prop = RNA_def_property(srna, "time_scale", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_float_sdna(prop, NULL, "time_scale");
+	RNA_def_property_range(prop, 0.0f, FLT_MAX);
+	RNA_def_property_ui_range(prop, 0.0f, 10.0f, 10, 3);
+	RNA_def_property_ui_text(prop, "Speed", "Cloth speed is multiplied by this value");
+	RNA_def_property_update(prop, 0, "rna_cloth_update");
+
 	prop = RNA_def_property(srna, "vertex_group_shrink", PROP_STRING, PROP_NONE);
 	RNA_def_property_string_funcs(prop, "rna_ClothSettings_shrink_vgroup_get", "rna_ClothSettings_shrink_vgroup_length",
 	                              "rna_ClothSettings_shrink_vgroup_set");

source/blender/physics/intern/BPH_mass_spring.cpp

@@ -376,7 +376,8 @@ BLI_INLINE void cloth_calc_spring_force(ClothModifierData *clmd, ClothSpring *s,
 		s->flags |= CLOTH_SPRING_FLAG_NEEDED;
 		
 		// current_position = xold + t * (newposition - xold)
-		interp_v3_v3v3(goal_x, verts[s->ij].xold, verts[s->ij].xconst, time);
+		/* divide by time_scale to prevent goal vertices' delta locations from being multiplied */
+		interp_v3_v3v3(goal_x, verts[s->ij].xold, verts[s->ij].xconst, time / parms->time_scale);
 		sub_v3_v3v3(goal_v, verts[s->ij].xconst, verts[s->ij].xold); // distance covered over dt==1
 		
 		scaling = parms->goalspring + s->stiffness * fabsf(parms->max_struct - parms->goalspring);
@@ -1004,6 +1005,8 @@ int BPH_cloth_solve(Object *ob, float frame, ClothModifierData *clmd, ListBase *
 				float v[3];
 				sub_v3_v3v3(v, verts[i].xconst, verts[i].xold);
 				// mul_v3_fl(v, clmd->sim_parms->stepsPerFrame);
+				/* divide by time_scale to prevent constrained velocities from being multiplied */
+				mul_v3_fl(v, 1.0f / clmd->sim_parms->time_scale);
 				BPH_mass_spring_set_velocity(id, i, v);
 			}
 		}
@@ -1070,7 +1073,8 @@ int BPH_cloth_solve(Object *ob, float frame, ClothModifierData *clmd, ListBase *
 			if (clmd->sim_parms->flags & CLOTH_SIMSETTINGS_FLAG_GOAL) {
 				if (verts[i].flags & CLOTH_VERT_FLAG_PINNED) {
 					float x[3];
-					interp_v3_v3v3(x, verts[i].xold, verts[i].xconst, step + dt);
+					/* divide by time_scale to prevent pinned vertices' delta locations from being multiplied */
+					interp_v3_v3v3(x, verts[i].xold, verts[i].xconst, (step + dt) / clmd->sim_parms->time_scale);
 					BPH_mass_spring_set_position(id, i, x);
 				}
 			}