Fix T76814: [Mantaflow] Surface Tension always works

Initialize the curvature grid and compute the laplacian only if the diffusion flag is set.

intern/mantaflow/intern/MANTA_main.cpp

@@ -71,6 +71,7 @@ MANTA::MANTA(int *res, FluidModifierData *mmd) : mCurrentID(++solverID)
   mUsingNoise = (mmd->domain->flags & FLUID_DOMAIN_USE_NOISE) && mUsingSmoke;
   mUsingFractions = (mmd->domain->flags & FLUID_DOMAIN_USE_FRACTIONS) && mUsingLiquid;
   mUsingMesh = (mmd->domain->flags & FLUID_DOMAIN_USE_MESH) && mUsingLiquid;
+  mUsingDiffusion = (mmd->domain->flags & FLUID_DOMAIN_USE_DIFFUSION) && mUsingLiquid;
   mUsingMVel = (mmd->domain->flags & FLUID_DOMAIN_USE_SPEED_VECTORS) && mUsingLiquid;
   mUsingGuiding = (mmd->domain->flags & FLUID_DOMAIN_USE_GUIDE);
   mUsingDrops = (mmd->domain->particle_type & FLUID_DOMAIN_PARTICLE_SPRAY) && mUsingLiquid;
@@ -219,6 +220,10 @@ MANTA::MANTA(int *res, FluidModifierData *mmd) : mCurrentID(++solverID)
       initLiquidMesh(mmd);
     }
 
+    if (mUsingDiffusion) {
+      initCurvature(mmd);
+    }
+
     if (mUsingGuiding) {
       mResGuiding = (mmd->domain->guide_parent) ? mmd->domain->guide_res : mmd->domain->res;
       initGuiding(mmd);
@@ -427,6 +432,16 @@ void MANTA::initLiquidMesh(FluidModifierData *mmd)
   mUsingMesh = true;
 }
 
+void MANTA::initCurvature(FluidModifierData *mmd)
+{
+  std::vector<std::string> pythonCommands;
+  std::string finalString = parseScript(liquid_alloc_curvature, mmd);
+  pythonCommands.push_back(finalString);
+
+  runPythonString(pythonCommands);
+  mUsingDiffusion = true;
+}
+
 void MANTA::initObstacle(FluidModifierData *mmd)
 {
   if (!mPhiObsIn) {

intern/mantaflow/intern/MANTA_main.h

@@ -66,6 +66,7 @@ struct MANTA {
   void initLiquid(FluidModifierData *mmd);
   void initLiquidMesh(FluidModifierData *mmd);
   void initObstacle(FluidModifierData *mmd);
+  void initCurvature(FluidModifierData *mmd);
   void initGuiding(FluidModifierData *mmd);
   void initFractions(FluidModifierData *mmd);
   void initInVelocity(FluidModifierData *mmd);
@@ -753,6 +754,7 @@ struct MANTA {
   bool mUsingOutflow;
   bool mUsingNoise;
   bool mUsingMesh;
+  bool mUsingDiffusion;
   bool mUsingMVel;
   bool mUsingLiquid;
   bool mUsingSmoke;

intern/mantaflow/intern/strings/liquid_script.h

@@ -80,11 +80,11 @@ mantaMsg('Liquid alloc')\n\
 phiParts_s$ID$   = s$ID$.create(LevelsetGrid)\n\
 phi_s$ID$        = s$ID$.create(LevelsetGrid)\n\
 phiTmp_s$ID$     = s$ID$.create(LevelsetGrid)\n\
-curvature_s$ID$  = s$ID$.create(RealGrid)\n\
 velOld_s$ID$     = s$ID$.create(MACGrid)\n\
 velParts_s$ID$   = s$ID$.create(MACGrid)\n\
 mapWeights_s$ID$ = s$ID$.create(MACGrid)\n\
 fractions_s$ID$  = None # allocated dynamically\n\
+curvature_s$ID$  = None\n\
 \n\
 pp_s$ID$         = s$ID$.create(BasicParticleSystem)\n\
 pVel_pp$ID$      = pp_s$ID$.create(PdataVec3)\n\
@@ -124,6 +124,11 @@ liquid_mesh_dict_s$ID$ = dict(lMesh=mesh_sm$ID$)\n\
 if using_speedvectors_s$ID$:\n\
     liquid_meshvel_dict_s$ID$ = dict(lVelMesh=mVel_mesh$ID$)\n";
 
+const std::string liquid_alloc_curvature =
+    "\n\
+mantaMsg('Liquid alloc curvature')\n\
+curvature_s$ID$  = s$ID$.create(RealGrid)\n";
+
 const std::string liquid_alloc_particles =
     "\n\
 ppSnd_sp$ID$         = sp$ID$.create(BasicParticleSystem)\n\
@@ -284,12 +289,13 @@ def liquid_step_$ID$():\n\
         alphaV = viscosity_s$ID$ * s$ID$.timestep * float(res_s$ID$*res_s$ID$)\n\
         setWallBcs(flags=flags_s$ID$, vel=vel_s$ID$, obvel=None if using_fractions_s$ID$ else obvel_s$ID$, phiObs=phiObs_s$ID$, fractions=fractions_s$ID$)\n\
         cgSolveDiffusion(flags_s$ID$, vel_s$ID$, alphaV)\n\
+        \n\
+        mantaMsg('Curvature')\n\
+        getLaplacian(laplacian=curvature_s$ID$, grid=phi_s$ID$)\n\
+        curvature_s$ID$.clamp(-1.0, 1.0)\n\
     \n\
     setWallBcs(flags=flags_s$ID$, vel=vel_s$ID$, obvel=None if using_fractions_s$ID$ else obvel_s$ID$, phiObs=phiObs_s$ID$, fractions=fractions_s$ID$)\n\
     \n\
-    mantaMsg('Calculating curvature')\n\
-    getLaplacian(laplacian=curvature_s$ID$, grid=phi_s$ID$)\n\
-    \n\
     if using_guiding_s$ID$:\n\
         mantaMsg('Guiding and pressure')\n\
         PD_fluid_guiding(vel=vel_s$ID$, velT=velT_s$ID$, flags=flags_s$ID$, phi=phi_s$ID$, curv=curvature_s$ID$, surfTens=surfaceTension_s$ID$, fractions=fractions_s$ID$, weight=weightGuide_s$ID$, blurRadius=beta_sg$ID$, pressure=pressure_s$ID$, tau=tau_sg$ID$, sigma=sigma_sg$ID$, theta=theta_sg$ID$, zeroPressureFixing=not doOpen_s$ID$)\n\