Fluid: Refactored fluid gravity settings

Refactored setup that converts from Blender to Mantaflow units.

6 files changed, 53 insertions, 55 deletions

diff --git a/intern/mantaflow/intern/MANTA_main.cpp b/intern/mantaflow/intern/MANTA_main.cpp
index a56ce4c1f60..9e5d9bf4656 100644
--- a/intern/mantaflow/intern/MANTA_main.cpp
+++ b/intern/mantaflow/intern/MANTA_main.cpp
@@ -711,6 +711,8 @@ std::string MANTA::getRealValue(const std::string &varName, FluidModifierData *m
       ss << mResZ;
     }
   }
+  else if (varName == "TIME_SCALE")
+    ss << mmd->domain->time_scale;
   else if (varName == "FRAME_LENGTH")
     ss << mmd->domain->frame_length;
   else if (varName == "CFL")
diff --git a/intern/mantaflow/intern/strings/fluid_script.h b/intern/mantaflow/intern/strings/fluid_script.h
index dd2111db7d7..c0a23f77d7a 100644
--- a/intern/mantaflow/intern/strings/fluid_script.h
+++ b/intern/mantaflow/intern/strings/fluid_script.h
@@ -92,7 +92,7 @@ const std::string fluid_variables =
 mantaMsg('Fluid variables')\n\
 dim_s$ID$     = $SOLVER_DIM$\n\
 res_s$ID$     = $RES$\n\
-gravity_s$ID$ = vec3($GRAVITY_X$, $GRAVITY_Y$, $GRAVITY_Z$)\n\
+gravity_s$ID$ = vec3($GRAVITY_X$, $GRAVITY_Y$, $GRAVITY_Z$) # in SI unit (e.g. m/s^2)\n\
 gs_s$ID$      = vec3($RESX$, $RESY$, $RESZ$)\n\
 maxVel_s$ID$  = 0\n\
 \n\
@@ -115,6 +115,7 @@ using_speedvectors_s$ID$ = $USING_SPEEDVECTORS$\n\
 using_diffusion_s$ID$    = $USING_DIFFUSION$\n\
 \n\
 # Fluid time params\n\
+timeScale_s$ID$    = $TIME_SCALE$\n\
 timeTotal_s$ID$    = $TIME_TOTAL$\n\
 timePerFrame_s$ID$ = $TIME_PER_FRAME$\n\
 frameLength_s$ID$  = $FRAME_LENGTH$\n\
@@ -132,8 +133,29 @@ end_frame_s$ID$     = $END_FRAME$\n\
 domainSize_s$ID$ = $FLUID_DOMAIN_SIZE$ # longest domain side in meters\n\
 viscosity_s$ID$ = $FLUID_VISCOSITY$ / (domainSize_s$ID$*domainSize_s$ID$) # kinematic viscosity in m^2/s\n\
 \n\
-# Factor to convert blender velocities to manta velocities\n\
-toMantaUnitsFac_s$ID$ = (1.0 / (1.0 / res_s$ID$))\n # = dt/dx * 1/dt ";
+# Factors to convert Blender units to Manta units\n\
+ratioMetersToRes_s$ID$ = float(domainSize_s$ID$) / float(res_s$ID$) # [meters / cells]\n\
+mantaMsg('1 Mantaflow cell is ' + str(ratioMetersToRes_s$ID$) + ' Blender length units long.')\n\
+\n\
+ratioResToBLength_s$ID$ = float(res_s$ID$) / float(domainSize_s$ID$) # [cells / blength] (blength: cm, m, or km, ... )\n\
+mantaMsg('1 Blender length unit is ' + str(ratioResToBLength_s$ID$) + ' Mantaflow cells long.')\n\
+\n\
+ratioBTimeToTimstep_s$ID$ = float(1) / float(0.1 * 25 * timeScale_s$ID$) # the time within 1 blender time unit, see also fluid.c\n\
+mantaMsg('1 Blender time unit is ' + str(ratioBTimeToTimstep_s$ID$) + ' Mantaflow time units long.')\n\
+\n\
+ratioFrameToFramelength_s$ID$ = float(1) / float(frameLength_s$ID$) # the time within 1 frame\n\
+mantaMsg('frame / frameLength is ' + str(ratioFrameToFramelength_s$ID$) + ' Mantaflow time units long.')\n\
+\n\
+scaleAcceleration_s$ID$ = ratioResToBLength_s$ID$ * (ratioBTimeToTimstep_s$ID$**2)# [meters/btime^2] to [cells/timestep^2] (btime: sec, min, or h, ...)\n\
+mantaMsg('scaleAcceleration is ' + str(scaleAcceleration_s$ID$))\n\
+\n\
+scaleSpeedFrames_s$ID$ = ratioResToBLength_s$ID$ * ratioFrameToFramelength_s$ID$ # [blength/frame] to [cells/frameLength]\n\
+mantaMsg('scaleSpeed is ' + str(scaleSpeedFrames_s$ID$))\n\
+\n\
+scaleSpeedTime_s$ID$ = ratioResToBLength_s$ID$ * ratioBTimeToTimstep_s$ID$ # [blength/btime] to [cells/frameLength]\n\
+mantaMsg('scaleSpeedTime is ' + str(scaleSpeedTime_s$ID$))\n\
+\n\
+gravity_s$ID$ *= scaleAcceleration_s$ID$ # scale from world acceleration to cell based acceleration\n";
 
 const std::string fluid_variables_noise =
     "\n\
@@ -342,17 +364,16 @@ def fluid_pre_step_$ID$():\n\
         y_obvel_s$ID$.safeDivide(numObs_s$ID$)\n\
         z_obvel_s$ID$.safeDivide(numObs_s$ID$)\n\
         \n\
-        x_obvel_s$ID$.multConst(toMantaUnitsFac_s$ID$)\n\
-        y_obvel_s$ID$.multConst(toMantaUnitsFac_s$ID$)\n\
-        z_obvel_s$ID$.multConst(toMantaUnitsFac_s$ID$)\n\
-        \n\
+        x_obvel_s$ID$.multConst(scaleSpeedFrames_s$ID$)\n\
+        y_obvel_s$ID$.multConst(scaleSpeedFrames_s$ID$)\n\
+        z_obvel_s$ID$.multConst(scaleSpeedFrames_s$ID$)\n\
         copyRealToVec3(sourceX=x_obvel_s$ID$, sourceY=y_obvel_s$ID$, sourceZ=z_obvel_s$ID$, target=obvelC_s$ID$)\n\
     \n\
     # translate invels (world space) to grid space\n\
     if using_invel_s$ID$:\n\
-        x_invel_s$ID$.multConst(toMantaUnitsFac_s$ID$)\n\
-        y_invel_s$ID$.multConst(toMantaUnitsFac_s$ID$)\n\
-        z_invel_s$ID$.multConst(toMantaUnitsFac_s$ID$)\n\
+        x_invel_s$ID$.multConst(scaleSpeedTime_s$ID$)\n\
+        y_invel_s$ID$.multConst(scaleSpeedTime_s$ID$)\n\
+        z_invel_s$ID$.multConst(scaleSpeedTime_s$ID$)\n\
         copyRealToVec3(sourceX=x_invel_s$ID$, sourceY=y_invel_s$ID$, sourceZ=z_invel_s$ID$, target=invelC_s$ID$)\n\
     \n\
     if using_guiding_s$ID$:\n\
@@ -362,9 +383,9 @@ def fluid_pre_step_$ID$():\n\
         velT_s$ID$.multConst(vec3(gamma_sg$ID$))\n\
     \n\
     # translate external forces (world space) to grid space\n\
-    x_force_s$ID$.multConst(toMantaUnitsFac_s$ID$)\n\
-    y_force_s$ID$.multConst(toMantaUnitsFac_s$ID$)\n\
-    z_force_s$ID$.multConst(toMantaUnitsFac_s$ID$)\n\
+    x_force_s$ID$.multConst(scaleSpeedFrames_s$ID$)\n\
+    y_force_s$ID$.multConst(scaleSpeedFrames_s$ID$)\n\
+    z_force_s$ID$.multConst(scaleSpeedFrames_s$ID$)\n\
     copyRealToVec3(sourceX=x_force_s$ID$, sourceY=y_force_s$ID$, sourceZ=z_force_s$ID$, target=forces_s$ID$)\n\
     \n\
     # If obstacle has velocity, i.e. is a moving obstacle, switch to dynamic preconditioner\n\
@@ -598,10 +619,9 @@ def bake_guiding_process_$ID$(framenr, format_guiding, path_guiding, resumable):
     y_guidevel_s$ID$.safeDivide(numGuides_s$ID$)\n\
     z_guidevel_s$ID$.safeDivide(numGuides_s$ID$)\n\
     \n\
-    x_guidevel_s$ID$.multConst(Real(toMantaUnitsFac_s$ID$))\n\
-    y_guidevel_s$ID$.multConst(Real(toMantaUnitsFac_s$ID$))\n\
-    z_guidevel_s$ID$.multConst(Real(toMantaUnitsFac_s$ID$))\n\
-    \n\
+    x_guidevel_s$ID$.multConst(scaleSpeedFrames_s$ID$)\n\
+    y_guidevel_s$ID$.multConst(scaleSpeedFrames_s$ID$)\n\
+    z_guidevel_s$ID$.multConst(scaleSpeedFrames_s$ID$)\n\
     copyRealToVec3(sourceX=x_guidevel_s$ID$, sourceY=y_guidevel_s$ID$, sourceZ=z_guidevel_s$ID$, target=guidevelC_s$ID$)\n\
     \n\
     mantaMsg('Extrapolating guiding velocity')\n\
diff --git a/intern/mantaflow/intern/strings/liquid_script.h b/intern/mantaflow/intern/strings/liquid_script.h
index f20b218427c..3aedde6753f 100644
--- a/intern/mantaflow/intern/strings/liquid_script.h
+++ b/intern/mantaflow/intern/strings/liquid_script.h
@@ -67,8 +67,7 @@ lMax_sp$ID$ = $SNDPARTICLE_L_MAX$\n\
 c_s_sp$ID$ = 0.4   # classification constant for snd parts\n\
 c_b_sp$ID$ = 0.77  # classification constant for snd parts\n\
 pot_radius_sp$ID$ = $SNDPARTICLE_POTENTIAL_RADIUS$\n\
-update_radius_sp$ID$ = $SNDPARTICLE_UPDATE_RADIUS$\n\
-scaleFromManta_sp$ID$ = $FLUID_DOMAIN_SIZE$ / float(res_s$ID$) # resize factor for snd parts\n";
+update_radius_sp$ID$ = $SNDPARTICLE_UPDATE_RADIUS$\n";
 
 //////////////////////////////////////////////////////////////////////
 // GRIDS & MESH & PARTICLESYSTEM
@@ -263,7 +262,7 @@ def liquid_step_$ID$():\n\
     velOld_s$ID$.copyFrom(vel_s$ID$)\n\
     \n\
     # forces & pressure solve\n\
-    addGravity(flags=flags_s$ID$, vel=vel_s$ID$, gravity=gravity_s$ID$)\n\
+    addGravity(flags=flags_s$ID$, vel=vel_s$ID$, gravity=gravity_s$ID$, scale=False)\n\
     \n\
     mantaMsg('Adding external forces')\n\
     addForceField(flags=flags_s$ID$, vel=vel_s$ID$, force=forces_s$ID$)\n\
@@ -371,7 +370,7 @@ def liquid_step_particles_$ID$():\n\
     flags_sp$ID$.updateFromLevelset(levelset=phi_sp$ID$)\n\
     \n\
     # Actual secondary particle simulation\n\
-    flipComputeSecondaryParticlePotentials(potTA=trappedAir_sp$ID$, potWC=waveCrest_sp$ID$, potKE=kineticEnergy_sp$ID$, neighborRatio=neighborRatio_sp$ID$, flags=flags_sp$ID$, v=vel_sp$ID$, normal=normal_sp$ID$, phi=phi_sp$ID$, radius=pot_radius_sp$ID$, tauMinTA=tauMin_ta_sp$ID$, tauMaxTA=tauMax_ta_sp$ID$, tauMinWC=tauMin_wc_sp$ID$, tauMaxWC=tauMax_wc_sp$ID$, tauMinKE=tauMin_k_sp$ID$, tauMaxKE=tauMax_k_sp$ID$, scaleFromManta=scaleFromManta_sp$ID$)\n\
+    flipComputeSecondaryParticlePotentials(potTA=trappedAir_sp$ID$, potWC=waveCrest_sp$ID$, potKE=kineticEnergy_sp$ID$, neighborRatio=neighborRatio_sp$ID$, flags=flags_sp$ID$, v=vel_sp$ID$, normal=normal_sp$ID$, phi=phi_sp$ID$, radius=pot_radius_sp$ID$, tauMinTA=tauMin_ta_sp$ID$, tauMaxTA=tauMax_ta_sp$ID$, tauMinWC=tauMin_wc_sp$ID$, tauMaxWC=tauMax_wc_sp$ID$, tauMinKE=tauMin_k_sp$ID$, tauMaxKE=tauMax_k_sp$ID$, scaleFromManta=ratioMetersToRes_s$ID$)\n\
     flipSampleSecondaryParticles(mode='single', flags=flags_sp$ID$, v=vel_sp$ID$, pts_sec=ppSnd_sp$ID$, v_sec=pVelSnd_pp$ID$, l_sec=pLifeSnd_pp$ID$, lMin=lMin_sp$ID$, lMax=lMax_sp$ID$, potTA=trappedAir_sp$ID$, potWC=waveCrest_sp$ID$, potKE=kineticEnergy_sp$ID$, neighborRatio=neighborRatio_sp$ID$, c_s=c_s_sp$ID$, c_b=c_b_sp$ID$, k_ta=k_ta_sp$ID$, k_wc=k_wc_sp$ID$, dt=sp$ID$.timestep)\n\
     flipUpdateSecondaryParticles(mode='linear', pts_sec=ppSnd_sp$ID$, v_sec=pVelSnd_pp$ID$, l_sec=pLifeSnd_pp$ID$, f_sec=pForceSnd_pp$ID$, flags=flags_sp$ID$, v=vel_sp$ID$, neighborRatio=neighborRatio_sp$ID$, radius=update_radius_sp$ID$, gravity=gravity_s$ID$, k_b=k_b_sp$ID$, k_d=k_d_sp$ID$, c_s=c_s_sp$ID$, c_b=c_b_sp$ID$, dt=sp$ID$.timestep)\n\
     if $SNDPARTICLE_BOUNDARY_PUSHOUT$:\n\
diff --git a/intern/mantaflow/intern/strings/smoke_script.h b/intern/mantaflow/intern/strings/smoke_script.h
index fdb58543cec..ea2b1e9d848 100644
--- a/intern/mantaflow/intern/strings/smoke_script.h
+++ b/intern/mantaflow/intern/strings/smoke_script.h
@@ -376,9 +376,9 @@ def smoke_step_$ID$():\n\
     \n\
     if using_heat_s$ID$:\n\
         mantaMsg('Adding heat buoyancy')\n\
-        addBuoyancy(flags=flags_s$ID$, density=heat_s$ID$, vel=vel_s$ID$, gravity=gravity_s$ID$, coefficient=buoyancy_heat_s$ID$)\n\
+        addBuoyancy(flags=flags_s$ID$, density=heat_s$ID$, vel=vel_s$ID$, gravity=gravity_s$ID$, coefficient=buoyancy_heat_s$ID$, scale=False)\n\
     mantaMsg('Adding buoyancy')\n\
-    addBuoyancy(flags=flags_s$ID$, density=density_s$ID$, vel=vel_s$ID$, gravity=gravity_s$ID$, coefficient=buoyancy_dens_s$ID$)\n\
+    addBuoyancy(flags=flags_s$ID$, density=density_s$ID$, vel=vel_s$ID$, gravity=gravity_s$ID$, coefficient=buoyancy_dens_s$ID$, scale=False)\n\
     \n\
     mantaMsg('Adding forces')\n\
     addForceField(flags=flags_s$ID$, vel=vel_s$ID$, force=forces_s$ID$)\n\
diff --git a/source/blender/blenkernel/intern/fluid.c b/source/blender/blenkernel/intern/fluid.c
index 1da6d9e3769..2b99133fe97 100644
--- a/source/blender/blenkernel/intern/fluid.c
+++ b/source/blender/blenkernel/intern/fluid.c
@@ -491,32 +491,6 @@ static void manta_set_domain_from_mesh(FluidDomainSettings *mds,
   mds->cell_size[2] /= (float)mds->base_res[2];
 }
 
-static void manta_set_domain_gravity(Scene *scene, FluidDomainSettings *mds)
-{
-  const float normalization_factor = 1.0f / 9.81f;
-
-  /* Use global gravity if enabled. */
-  if (scene->physics_settings.flag & PHYS_GLOBAL_GRAVITY) {
-    float gravity[3];
-    copy_v3_v3(gravity, scene->physics_settings.gravity);
-    /* Map default value to 1.0. */
-    mul_v3_fl(gravity, normalization_factor);
-
-    /* Convert gravity to domain space. */
-    float gravity_mag = len_v3(gravity);
-    mul_mat3_m4_v3(mds->imat, gravity);
-    normalize_v3(gravity);
-    mul_v3_fl(gravity, gravity_mag);
-
-    copy_v3_v3(mds->gravity, gravity);
-  }
-  else {
-    mul_v3_fl(mds->gravity, normalization_factor);
-  }
-
-  mul_v3_fl(mds->gravity, mds->effector_weights->global_gravity);
-}
-
 static bool BKE_fluid_modifier_init(
     FluidModifierData *mmd, Depsgraph *depsgraph, Object *ob, Scene *scene, Mesh *me)
 {
@@ -527,8 +501,11 @@ static bool BKE_fluid_modifier_init(
     int res[3];
     /* Set domain dimensions from mesh. */
     manta_set_domain_from_mesh(mds, ob, me, true);
-    /* Set domain gravity. */
-    manta_set_domain_gravity(scene, mds);
+    /* Set domain gravity, use global gravity if enabled. */
+    if (scene->physics_settings.flag & PHYS_GLOBAL_GRAVITY) {
+      copy_v3_v3(mds->gravity, scene->physics_settings.gravity);
+    }
+    mul_v3_fl(mds->gravity, mds->effector_weights->global_gravity);
     /* Reset domain values. */
     zero_v3_int(mds->shift);
     zero_v3(mds->shift_f);
@@ -1996,9 +1973,9 @@ static void sample_mesh(FluidFlowSettings *mfs,
         normalize_v3(hit_normal);
 
         /* Apply normal directional velocity. */
-        velocity_map[index * 3] += hit_normal[0] * mfs->vel_normal * 0.25f;
-        velocity_map[index * 3 + 1] += hit_normal[1] * mfs->vel_normal * 0.25f;
-        velocity_map[index * 3 + 2] += hit_normal[2] * mfs->vel_normal * 0.25f;
+        velocity_map[index * 3] += hit_normal[0] * mfs->vel_normal;
+        velocity_map[index * 3 + 1] += hit_normal[1] * mfs->vel_normal;
+        velocity_map[index * 3 + 2] += hit_normal[2] * mfs->vel_normal;
       }
       /* Apply object velocity. */
       if (has_velocity && mfs->vel_multi) {
diff --git a/source/blender/makesrna/intern/rna_fluid.c b/source/blender/makesrna/intern/rna_fluid.c
index 0a6554a1cea..86860e5e14b 100644
--- a/source/blender/makesrna/intern/rna_fluid.c
+++ b/source/blender/makesrna/intern/rna_fluid.c
@@ -2467,7 +2467,7 @@ static void rna_def_fluid_flow_settings(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Random", "Amount of random velocity");
   RNA_def_property_update(prop, NC_OBJECT | ND_MODIFIER, "rna_Fluid_flow_reset");
 
-  prop = RNA_def_property(srna, "velocity_coord", PROP_FLOAT, PROP_XYZ);
+  prop = RNA_def_property(srna, "velocity_coord", PROP_FLOAT, PROP_VELOCITY);
   RNA_def_property_float_sdna(prop, NULL, "vel_coord");
   RNA_def_property_array(prop, 3);
   RNA_def_property_range(prop, -1000.1, 1000.1);