Completely refactored sph fluid particles. Only the very core of the algorithm remains

the same, but big changes have happened both on the outside and on the inside.

New UI:
* The old parameters were quite true to the underlying algorithm, but were quite obscure
  from a users point of view. Now there are only a few intuitive basic parameters that
  define the basic fluid behavior.
** By default particle size is now used to determine the interaction radius, rest
   density and spring rest lengths so that it's easy to get stable simulations by simply
   emitting particles for a few frames and adjusting the particle size (easy when the
   particle size is drawn) so that the fluid appears continuous (particles are touching
   eachother).
** Stiffness - in reality most fluids are very incompressible, but this is a very hard
   problem to solve with particle based fluid simulation so some compromises have to be
   made. So the bigger the stiffness parameter is the less the fluid will compress under
   stress, but the more substeps are needed for stable simulation.
** Viscosity - how much internal friction there is in the fluid. Large viscosities also
   smooth out instabilities, so less viscous fluids again need more substeps to remain
   stable.
** Buoancy - with high buoancy low pressure areas inside the fluid start to rise against
   gravity, and high pressure areas start to come down.

* In addition to these basic parameters there are separate advanced parameters that can
  either be tweaked relative to the basic parameters (or particle size) or defined
  independently.
** Repulsion - the stiffness parameter tries to keep the fluid density constant, but this
   can lead to small clumps of particles, so the repulsion keeps the particles better
   separated.
** Stiff viscosity - the normal viscosity only applies when particles are moving closer to 
   eachother to allow free flowing fluids. Stiff viscosity also applies smoothing to
   particles that are moving away from eachother.
** Interaction radius - by default this is 4 * particle size.
** Rest density - by default this is a density that the particles have when they're packed
   densely next to eachother.
** Spring rest length - by default this is 2 * particle size.

* There are also new options for 3d view particle coloring in the display panel to show
  particle velocity and acceleration. These make it easier to see what's happening in the
  fluid simulations, but can of course be used with other particles as well.

* Viscoelastic springs have some new options too. The plasticity can now be set to much
  higher values for instant deletion of springs as the elastic limit is exeeded. In addition
  to that there is an option to only create springs for a certain number of frames when a
  particle is born. These options give new possibilities for breaking viscoelastic fluids.

New in the code:
* Most of the fluids code is now thread safe, so when particle dynamics go threaded there
  will be a nice speed boost to fluids as well.
* Fluids now use a bvh-tree instead of a kd-tree for the neighbor lookups. The bvh-tree 
  implementation makes the code quite a bit cleaner and should also give a slight speed
  boost to the simulation too.
* Previously only force fields were calculated with the different integration methods, but
  now the fluid calculations are also done using the selected integration method, so there
  are again more choices in effecting simulation accuracy and stability. This change also
  included a nice cleanup of the whole particle integration code.

As the internals are pretty stirred up old particle fluid simulations will probably not
work correctly straight away, but with some tweaking the same level of control is still
available by not using the "relative versions" of the advanced parameters (by default these
are not used when loading old files).

1 files changed, 68 insertions, 22 deletions

diff --git a/source/blender/makesrna/intern/rna_particle.c b/source/blender/makesrna/intern/rna_particle.c
index 57d6e72a102..069f674bf4a 100644
--- a/source/blender/makesrna/intern/rna_particle.c
+++ b/source/blender/makesrna/intern/rna_particle.c
@@ -1073,10 +1073,9 @@ static void rna_def_fluid_settings(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Interaction Radius", "Fluid interaction radius");
  	RNA_def_property_update(prop, 0, "rna_Particle_reset");
 
-	/* Hidden in ui to give a little easier user experience. */
  	prop= RNA_def_property(srna, "rest_length", PROP_FLOAT, PROP_NONE);
- 	RNA_def_property_range(prop, 0.0f, 1.0f);
-	RNA_def_property_ui_text(prop, "Rest Length", "Spring rest length (factor of interaction radius)");
+ 	RNA_def_property_range(prop, 0.0f, 2.0f);
+	RNA_def_property_ui_text(prop, "Rest Length", "Spring rest length (factor of particle radius)");
  	RNA_def_property_update(prop, 0, "rna_Particle_reset");
 
 	prop= RNA_def_property(srna, "use_viscoelastic_springs", PROP_BOOLEAN, PROP_NONE);
@@ -1086,12 +1085,12 @@ static void rna_def_fluid_settings(BlenderRNA *brna)
 
 	prop= RNA_def_property(srna, "use_initial_rest_length", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "flag", SPH_CURRENT_REST_LENGTH);
-	RNA_def_property_ui_text(prop, "Initial Rest Length", "Use the initial length as spring rest length instead of interaction radius/2");
+	RNA_def_property_ui_text(prop, "Initial Rest Length", "Use the initial length as spring rest length instead of 2 * particle size");
 	RNA_def_property_update(prop, 0, "rna_Particle_reset");
 
  	prop= RNA_def_property(srna, "plasticity", PROP_FLOAT, PROP_NONE);
  	RNA_def_property_float_sdna(prop, NULL, "plasticity_constant");
- 	RNA_def_property_range(prop, 0.0f, 1.0f);
+ 	RNA_def_property_range(prop, 0.0f, 100.0f);
  	RNA_def_property_ui_text(prop, "Plasticity", "How much the spring rest length can change after the elastic limit is crossed");
  	RNA_def_property_update(prop, 0, "rna_Particle_reset");
 
@@ -1100,6 +1099,11 @@ static void rna_def_fluid_settings(BlenderRNA *brna)
  	RNA_def_property_range(prop, 0.0f, 1.0f);
  	RNA_def_property_ui_text(prop, "Elastic Limit", "How much the spring has to be stretched/compressed in order to change it's rest length");
  	RNA_def_property_update(prop, 0, "rna_Particle_reset");
+
+ 	prop= RNA_def_property(srna, "spring_frames", PROP_INT, PROP_NONE);
+ 	RNA_def_property_range(prop, 0.0f, 100.0f);
+ 	RNA_def_property_ui_text(prop, "Spring Frames", "Create springs for this number of frames since particles birth (0 is always)");
+ 	RNA_def_property_update(prop, 0, "rna_Particle_reset");
  
  	/* Viscosity */
  	prop= RNA_def_property(srna, "linear_viscosity", PROP_FLOAT, PROP_NONE);
@@ -1109,42 +1113,69 @@ static void rna_def_fluid_settings(BlenderRNA *brna)
  	RNA_def_property_ui_text(prop, "Viscosity", "Linear viscosity");
 	RNA_def_property_update(prop, 0, "rna_Particle_reset");
   
- 	prop= RNA_def_property(srna, "square_viscosity", PROP_FLOAT, PROP_NONE);
+ 	prop= RNA_def_property(srna, "stiff_viscosity", PROP_FLOAT, PROP_NONE);
 	RNA_def_property_float_sdna(prop, NULL, "viscosity_beta");
 	RNA_def_property_range(prop, 0.0f, 100.0f);
-	RNA_def_property_ui_range(prop, 0.0f, 10.0f, 1, 3);
- 	RNA_def_property_ui_text(prop, "Square viscosity", "Square viscosity");
+	RNA_def_property_ui_range(prop, 0.0f, 2.0f, 1, 3);
+ 	RNA_def_property_ui_text(prop, "Stiff viscosity", "Creates viscosity for expanding fluid)");
  	RNA_def_property_update(prop, 0, "rna_Particle_reset");
 
 	/* Double density relaxation */
- 	prop= RNA_def_property(srna, "density_force", PROP_FLOAT, PROP_NONE);
+ 	prop= RNA_def_property(srna, "stiffness", PROP_FLOAT, PROP_NONE);
  	RNA_def_property_float_sdna(prop, NULL, "stiffness_k");
  	RNA_def_property_range(prop, 0.0f, 100.0f);
 	RNA_def_property_ui_range(prop, 0.0f, 10.0f, 1, 3);
- 	RNA_def_property_ui_text(prop, "Density Force", "How strongly the fluid tends to rest density");
+ 	RNA_def_property_ui_text(prop, "Stiffness", "How incompressible the fluid is");
 	RNA_def_property_update(prop, 0, "rna_Particle_reset");
   
- 	prop= RNA_def_property(srna, "repulsion_force", PROP_FLOAT, PROP_NONE);
+ 	prop= RNA_def_property(srna, "repulsion", PROP_FLOAT, PROP_NONE);
  	RNA_def_property_float_sdna(prop, NULL, "stiffness_knear");
 	RNA_def_property_range(prop, 0.0f, 100.0f);
-	RNA_def_property_ui_range(prop, 0.0f, 10.0f, 1, 3);
- 	RNA_def_property_ui_text(prop, "Repulsion", "How strongly the fluid tries to keep from clustering");
+	RNA_def_property_ui_range(prop, 0.0f, 2.0f, 1, 3);
+ 	RNA_def_property_ui_text(prop, "Repulsion Factor", "How strongly the fluid tries to keep from clustering (factor of stiffness)");
  	RNA_def_property_update(prop, 0, "rna_Particle_reset");
   
  	prop= RNA_def_property(srna, "rest_density", PROP_FLOAT, PROP_NONE);
 	RNA_def_property_float_sdna(prop, NULL, "rest_density");
- 	RNA_def_property_range(prop, 0.0f, 1000.0f);
-	RNA_def_property_ui_range(prop, 0.0f, 100.0f, 1, 3);
- 	RNA_def_property_ui_text(prop, "Rest Density", "Rest density of the fluid");
+ 	RNA_def_property_range(prop, 0.0f, 100.0f);
+	RNA_def_property_ui_range(prop, 0.0f, 2.0f, 1, 3);
+ 	RNA_def_property_ui_text(prop, "Rest Density", "Fluid rest density");
  	RNA_def_property_update(prop, 0, "rna_Particle_reset");
 	
 	/* Buoyancy */
 	prop= RNA_def_property(srna, "buoyancy", PROP_FLOAT, PROP_NONE);
  	RNA_def_property_float_sdna(prop, NULL, "buoyancy");
- 	RNA_def_property_range(prop, 0.0f, 1.0f);
+ 	RNA_def_property_range(prop, 0.0f, 10.0f);
+	RNA_def_property_ui_range(prop, 0.0f, 1.0f, 1, 3);
  	RNA_def_property_ui_text(prop, "Buoyancy", "Artificial buoyancy force in negative gravity direction based on pressure differences inside the fluid");
  	RNA_def_property_update(prop, 0, "rna_Particle_reset");
+
+	/* Factor flags */
 	
+	prop= RNA_def_property(srna, "factor_repulsion", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "flag", SPH_FAC_REPULSION);
+	RNA_def_property_ui_text(prop, "Factor Repulsion", "Repulsion is a factor of stiffness");
+	RNA_def_property_update(prop, 0, "rna_Particle_reset");
+
+	prop= RNA_def_property(srna, "factor_density", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "flag", SPH_FAC_DENSITY);
+	RNA_def_property_ui_text(prop, "Factor Density", "Density is calculated as a factor of default density (depends on particle size)");
+	RNA_def_property_update(prop, 0, "rna_Particle_reset");
+
+	prop= RNA_def_property(srna, "factor_radius", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "flag", SPH_FAC_RADIUS);
+	RNA_def_property_ui_text(prop, "Factor Radius", "Interaction radius is a factor of 4 * particle size");
+	RNA_def_property_update(prop, 0, "rna_Particle_reset");
+
+	prop= RNA_def_property(srna, "factor_stiff_viscosity", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "flag", SPH_FAC_VISCOSITY);
+	RNA_def_property_ui_text(prop, "Factor Stiff Viscosity", "Stiff viscosity is a factor of normal viscosity");
+	RNA_def_property_update(prop, 0, "rna_Particle_reset");
+
+	prop= RNA_def_property(srna, "factor_rest_length", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "flag", SPH_FAC_REST_LENGTH);
+	RNA_def_property_ui_text(prop, "Factor Rest Length", "Spring rest length is a factor of 2 * particle size");
+	RNA_def_property_update(prop, 0, "rna_Particle_reset");
 }
 
 static void rna_def_particle_settings_mtex(BlenderRNA *brna)
@@ -1483,6 +1514,14 @@ static void rna_def_particle_settings(BlenderRNA *brna)
 		{0, NULL, 0, NULL, NULL}
 	};
 
+	static EnumPropertyItem draw_col_items[] = {
+		{PART_DRAW_COL_NONE, "NONE", 0, "None", ""},
+		{PART_DRAW_COL_MAT, "MATERIAL", 0, "Material", ""},
+		{PART_DRAW_COL_VEL, "VELOCITY", 0, "Velocity", ""},
+		{PART_DRAW_COL_ACC, "ACCELERATION", 0, "Acceleration", ""},
+		{0, NULL, 0, NULL, NULL}
+	};
+
 	srna= RNA_def_struct(brna, "ParticleSettings", "ID");
 	RNA_def_struct_ui_text(srna, "Particle Settings", "Particle settings, reusable by multiple particle systems");
 	RNA_def_struct_ui_icon(srna, ICON_PARTICLE_DATA);
@@ -1725,11 +1764,6 @@ static void rna_def_particle_settings(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Speed", "Multiply line length by particle speed");
 	RNA_def_property_update(prop, 0, "rna_Particle_redo");
 
-	prop= RNA_def_property(srna, "show_material_color", PROP_BOOLEAN, PROP_NONE);
-	RNA_def_property_boolean_sdna(prop, NULL, "draw", PART_DRAW_MAT_COL);
-	RNA_def_property_ui_text(prop, "Material Color", "Draw particles using material's diffuse color");
-	RNA_def_property_update(prop, 0, "rna_Particle_redo");
-
 	prop= RNA_def_property(srna, "use_whole_group", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "draw", PART_DRAW_WHOLE_GR);
 	RNA_def_property_ui_text(prop, "Whole Group", "Use whole group at once");
@@ -1754,6 +1788,12 @@ static void rna_def_particle_settings(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Particle Rendering", "How particles are rendered");
 	RNA_def_property_update(prop, 0, "rna_Particle_redo");
 
+	prop= RNA_def_property(srna, "draw_color", PROP_ENUM, PROP_NONE);
+	RNA_def_property_enum_sdna(prop, NULL, "draw_col");
+	RNA_def_property_enum_items(prop, draw_col_items);
+	RNA_def_property_ui_text(prop, "Draw Color", "Draw additional particle data as a color");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo");
+
 	prop= RNA_def_property(srna, "draw_size", PROP_INT, PROP_NONE);
 	RNA_def_property_range(prop, 0, 1000);
 	RNA_def_property_ui_range(prop, 0, 100, 1, 0);
@@ -1865,6 +1905,12 @@ static void rna_def_particle_settings(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Tilt", "Tilt of the billboards");
 	RNA_def_property_update(prop, 0, "rna_Particle_redo");
 
+	prop= RNA_def_property(srna, "color_maximum", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_float_sdna(prop, NULL, "color_vec_max");
+	RNA_def_property_range(prop, 0.01f, 100.0f);
+	RNA_def_property_ui_text(prop, "Color Maximum", "Maximum length of the particle color vector");
+	RNA_def_property_update(prop, 0, "rna_Particle_redo");
+
 	prop= RNA_def_property(srna, "billboard_tilt_random", PROP_FLOAT, PROP_NONE);
 	RNA_def_property_float_sdna(prop, NULL, "bb_rand_tilt");
 	RNA_def_property_range(prop, 0.0f, 1.0f);