Fluid: Initial support for 2D fluid simulations

Initial adjustments for 2D (real-time) simulations.

Basic functionality includes:
- 2D/3D switcher in domain settings
- 2D simulation support for smoke/fire, wavelet noise, liquid
particles, secondary particles
- UI switcher to choose the axis that will be simulated on
- Planar visualization in workbench render

Some things that remain to do (non-exhaustive list):
- Eevee & Cycles support
- Liquid meshing
- Liquid viscosity solver

intern/mantaflow/extern/manta_fluid_API.h

@@ -103,6 +103,7 @@ float *manta_get_num_guide(struct MANTA *fluid);
 int manta_get_res_x(struct MANTA *fluid);
 int manta_get_res_y(struct MANTA *fluid);
 int manta_get_res_z(struct MANTA *fluid);
+void manta_get_res(struct MANTA *fluid, int* res);
 float *manta_get_phi_in(struct MANTA *fluid);
 float *manta_get_phistatic_in(struct MANTA *fluid);
 float *manta_get_phiobs_in(struct MANTA *fluid);

intern/mantaflow/intern/MANTA_main.cpp

@@ -204,6 +204,14 @@ MANTA::MANTA(int *res, FluidModifierData *fmd)
       mResXParticle = mUpresParticle * mResX;
       mResYParticle = mUpresParticle * mResY;
       mResZParticle = mUpresParticle * mResZ;
+      if (fds->solver_res == FLUID_DOMAIN_DIMENSION_2D) {
+        if (fds->slice_axis == SLICE_AXIS_X)
+          mResXParticle = 1;
+        else if (fds->slice_axis == SLICE_AXIS_Y)
+          mResYParticle = 1;
+        else if (fds->slice_axis == SLICE_AXIS_Z)
+          mResZParticle = 1;
+      }
       mTotalCellsParticles = mResXParticle * mResYParticle * mResZParticle;
 
       initSuccess &= initSndParts();
@@ -266,6 +274,14 @@ MANTA::MANTA(int *res, FluidModifierData *fmd)
       mResXNoise = amplify * mResX;
       mResYNoise = amplify * mResY;
       mResZNoise = amplify * mResZ;
+      if (fds->solver_res == FLUID_DOMAIN_DIMENSION_2D) {
+        if (fds->slice_axis == SLICE_AXIS_X)
+          mResXNoise = 1;
+        else if (fds->slice_axis == SLICE_AXIS_Y)
+          mResYNoise = 1;
+        else if (fds->slice_axis == SLICE_AXIS_Z)
+          mResZNoise = 1;
+      }
       mTotalCellsHigh = mResXNoise * mResYNoise * mResZNoise;
 
       /* Initialize Mantaflow variables in Python. */
@@ -785,8 +801,10 @@ void MANTA::initializeRNAMap(FluidModifierData *fmd)
   mRNAMap["BOUND_CONDITIONS"] = borderCollisions;
   mRNAMap["BOUNDARY_WIDTH"] = to_string(fds->boundary_width);
   mRNAMap["RES"] = to_string(mMaxRes);
-  mRNAMap["RESX"] = to_string(mResX);
+  mRNAMap["RESX"] = (is2D && fds->slice_axis == SLICE_AXIS_X) ? to_string(mResY) :
-  mRNAMap["RESY"] = (is2D) ? to_string(mResZ) : to_string(mResY);
+                                                                to_string(mResX);
+  mRNAMap["RESY"] = (is2D && fds->slice_axis != SLICE_AXIS_Z) ? to_string(mResZ) :
+                                                                to_string(mResY);
   mRNAMap["RESZ"] = (is2D) ? to_string(1) : to_string(mResZ);
   mRNAMap["TIME_SCALE"] = to_string(fds->time_scale);
   mRNAMap["FRAME_LENGTH"] = to_string(fds->frame_length);
@@ -801,14 +819,18 @@ void MANTA::initializeRNAMap(FluidModifierData *fmd)
   mRNAMap["NOISE_SCALE"] = to_string(fds->noise_scale);
   mRNAMap["MESH_SCALE"] = to_string(fds->mesh_scale);
   mRNAMap["PARTICLE_SCALE"] = to_string(fds->particle_scale);
-  mRNAMap["NOISE_RESX"] = to_string(mResXNoise);
+  mRNAMap["NOISE_RESX"] = (is2D && fds->slice_axis == SLICE_AXIS_X) ? to_string(mResYNoise) :
-  mRNAMap["NOISE_RESY"] = (is2D) ? to_string(mResZNoise) : to_string(mResYNoise);
+                                                                      to_string(mResXNoise);
+  mRNAMap["NOISE_RESY"] = (is2D && fds->slice_axis != SLICE_AXIS_Z) ? to_string(mResZNoise) :
+                                                                      to_string(mResYNoise);
   mRNAMap["NOISE_RESZ"] = (is2D) ? to_string(1) : to_string(mResZNoise);
   mRNAMap["MESH_RESX"] = to_string(mResXMesh);
   mRNAMap["MESH_RESY"] = (is2D) ? to_string(mResZMesh) : to_string(mResYMesh);
   mRNAMap["MESH_RESZ"] = (is2D) ? to_string(1) : to_string(mResZMesh);
-  mRNAMap["PARTICLE_RESX"] = to_string(mResXParticle);
+  mRNAMap["PARTICLE_RESX"] = (is2D && fds->slice_axis == SLICE_AXIS_X) ? to_string(mResYParticle) :
-  mRNAMap["PARTICLE_RESY"] = (is2D) ? to_string(mResZParticle) : to_string(mResYParticle);
+                                                                         to_string(mResXParticle);
+  mRNAMap["PARTICLE_RESY"] = (is2D && fds->slice_axis != SLICE_AXIS_Z) ? to_string(mResZParticle) :
+                                                                         to_string(mResYParticle);
   mRNAMap["PARTICLE_RESZ"] = (is2D) ? to_string(1) : to_string(mResZParticle);
   mRNAMap["GUIDING_RESX"] = to_string(mResGuiding[0]);
   mRNAMap["GUIDING_RESY"] = (is2D) ? to_string(mResGuiding[2]) : to_string(mResGuiding[1]);

intern/mantaflow/intern/manta_fluid_API.cpp

@@ -279,6 +279,12 @@ int manta_get_res_z(MANTA *fluid)
 {
   return fluid->getResZ();
 }
+void manta_get_res(MANTA *smoke, int *res)
+{
+  res[0] = smoke->getResX();
+  res[1] = smoke->getResY();
+  res[2] = smoke->getResZ();
+}
 
 float *manta_get_phi_in(MANTA *fluid)
 {

intern/mantaflow/intern/strings/fluid_script.h

@@ -62,22 +62,22 @@ s$ID$ = Solver(name='solver_base$ID$', gridSize=gs_s$ID$, dim=dim_s$ID$)\n";
 const std::string fluid_solver_noise =
     "\n\
 mantaMsg('Solver noise')\n\
-sn$ID$ = Solver(name='solver_noise$ID$', gridSize=gs_sn$ID$)\n";
+sn$ID$ = Solver(name='solver_noise$ID$', gridSize=gs_sn$ID$, dim=dim_s$ID$)\n";
 
 const std::string fluid_solver_mesh =
     "\n\
 mantaMsg('Solver mesh')\n\
-sm$ID$ = Solver(name='solver_mesh$ID$', gridSize=gs_sm$ID$)\n";
+sm$ID$ = Solver(name='solver_mesh$ID$', gridSize=gs_sm$ID$, dim=dim_s$ID$)\n";
 
 const std::string fluid_solver_particles =
     "\n\
 mantaMsg('Solver particles')\n\
-sp$ID$ = Solver(name='solver_particles$ID$', gridSize=gs_sp$ID$)\n";
+sp$ID$ = Solver(name='solver_particles$ID$', gridSize=gs_sp$ID$, dim=dim_s$ID$)\n";
 
 const std::string fluid_solver_guiding =
     "\n\
 mantaMsg('Solver guiding')\n\
-sg$ID$ = Solver(name='solver_guiding$ID$', gridSize=gs_sg$ID$)\n";
+sg$ID$ = Solver(name='solver_guiding$ID$', gridSize=gs_sg$ID$, dim=dim_s$ID$)\n";
 
 const std::string fluid_solver_viscosity =
     "\n\
@@ -95,6 +95,11 @@ dim_s$ID$     = $SOLVER_DIM$\n\
 res_s$ID$     = $RES$\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\
+if dim_s$ID$ == 2:\n\
+    gs_s$ID$.z = 1\n\
+    gravity_s$ID$.y = gravity_s$ID$.z\n\
+    gravity_s$ID$.z = 0\n\
+\n\
 maxVel_s$ID$  = 0\n\
 \n\
 domainClosed_s$ID$     = $DOMAIN_CLOSED$\n\
@@ -178,24 +183,32 @@ const std::string fluid_variables_noise =
     "\n\
 mantaMsg('Fluid variables noise')\n\
 upres_sn$ID$  = $NOISE_SCALE$\n\
-gs_sn$ID$     = vec3(upres_sn$ID$*gs_s$ID$.x, upres_sn$ID$*gs_s$ID$.y, upres_sn$ID$*gs_s$ID$.z)\n";
+gs_sn$ID$     = vec3(upres_sn$ID$*gs_s$ID$.x, upres_sn$ID$*gs_s$ID$.y, upres_sn$ID$*gs_s$ID$.z)\n\
+if dim_s$ID$ == 2:\n\
+    gs_sn$ID$.z = 1\n";
 
 const std::string fluid_variables_mesh =
     "\n\
 mantaMsg('Fluid variables mesh')\n\
 upres_sm$ID$  = $MESH_SCALE$\n\
-gs_sm$ID$     = vec3(upres_sm$ID$*gs_s$ID$.x, upres_sm$ID$*gs_s$ID$.y, upres_sm$ID$*gs_s$ID$.z)\n";
+gs_sm$ID$     = vec3(upres_sm$ID$*gs_s$ID$.x, upres_sm$ID$*gs_s$ID$.y, upres_sm$ID$*gs_s$ID$.z)\n\
+if dim_s$ID$ == 2:\n\
+    gs_sm$ID$.z = 1\n";
 
 const std::string fluid_variables_particles =
     "\n\
 mantaMsg('Fluid variables particles')\n\
 upres_sp$ID$  = $PARTICLE_SCALE$\n\
-gs_sp$ID$     = vec3(upres_sp$ID$*gs_s$ID$.x, upres_sp$ID$*gs_s$ID$.y, upres_sp$ID$*gs_s$ID$.z)\n";
+gs_sp$ID$     = vec3(upres_sp$ID$*gs_s$ID$.x, upres_sp$ID$*gs_s$ID$.y, upres_sp$ID$*gs_s$ID$.z)\n\
+if dim_s$ID$ == 2:\n\
+    gs_sp$ID$.z = 1\n";
 
 const std::string fluid_variables_guiding =
     "\n\
 mantaMsg('Fluid variables guiding')\n\
 gs_sg$ID$   = vec3($GUIDING_RESX$, $GUIDING_RESY$, $GUIDING_RESZ$)\n\
+if dim_s$ID$ == 2:\n\
+    gs_sg$ID$.z = 1\n\
 \n\
 alpha_sg$ID$ = $GUIDING_ALPHA$\n\
 beta_sg$ID$  = $GUIDING_BETA$\n\
@@ -206,7 +219,9 @@ theta_sg$ID$ = 1.0\n";
 
 const std::string fluid_variables_viscosity =
     "\n\
-gs_sv$ID$    = vec3($RESX$*2, $RESY$*2, $RESZ$*2)\n";
+gs_sv$ID$    = vec3($RESX$*2, $RESY$*2, $RESZ$*2)\n\
+if dim_s$ID$ == 2:\n\
+    gs_sv$ID$.z = 1\n";
 
 const std::string fluid_with_obstacle =
     "\n\

release/scripts/startup/bl_ui/properties_physics_fluid.py

@@ -197,6 +197,9 @@ class PHYSICS_PT_settings(PhysicButtonsPanel, Panel):
             if PhysicButtonsPanel.poll_gas_domain(context):
                 col.prop(domain, "clipping", text="Empty Space")
             col.prop(domain, "delete_in_obstacle", text="Delete in Obstacle")
+            col.prop(domain, "solver_res", text="Dimension")
+            if domain.solver_res == '2D':
+                col.prop(domain, "slice_axis", text="Axis")
 
             if domain.cache_type == 'MODULAR':
                 col.separator()
@@ -1379,6 +1382,7 @@ class PHYSICS_PT_viewport_display_slicing(PhysicButtonsPanel, Panel):
         layout.active = domain.use_slice
 
         col = layout.column()
+        if domain.solver_res == '3D':
             col.prop(domain, "slice_axis")
         col.prop(domain, "slice_depth")
 

source/blender/blenkernel/BKE_fluid.h

@@ -89,6 +89,9 @@ void BKE_fluid_particles_set(struct FluidDomainSettings *settings, int value, bo
 void BKE_fluid_domain_type_set(struct Object *object,
                                struct FluidDomainSettings *settings,
                                int type);
+void BKE_fluid_domain_solver_res_set(struct Object *object,
+                                     struct FluidDomainSettings *settings,
+                                     int type);
 void BKE_fluid_flow_type_set(struct Object *object, struct FluidFlowSettings *settings, int type);
 void BKE_fluid_effector_type_set(struct Object *object,
                                  struct FluidEffectorSettings *settings,

source/blender/blenkernel/intern/fluid.c

@@ -126,10 +126,6 @@ bool BKE_fluid_reallocate_fluid(FluidDomainSettings *fds, int res[3], int free_o
   }
   else {
     fds->fluid = manta_init(res, fds->fmd);
-
-    fds->res_noise[0] = res[0] * fds->noise_scale;
-    fds->res_noise[1] = res[1] * fds->noise_scale;
-    fds->res_noise[2] = res[2] * fds->noise_scale;
   }
 
   return (fds->fluid != NULL);
@@ -145,7 +141,10 @@ void BKE_fluid_reallocate_copy_fluid(FluidDomainSettings *fds,
                                      int n_shift[3])
 {
   struct MANTA *fluid_old = fds->fluid;
-  const int block_size = fds->noise_scale;
+  int block_size[3] = {fds->noise_scale, fds->noise_scale, fds->noise_scale};
+  if (fds->solver_res == FLUID_DOMAIN_DIMENSION_2D) {
+    block_size[fds->slice_axis - 1] = 1;
+  }
   int new_shift[3] = {0};
   sub_v3_v3v3_int(new_shift, n_shift, o_shift);
 
@@ -210,8 +209,9 @@ void BKE_fluid_reallocate_copy_fluid(FluidDomainSettings *fds,
     float *n_wt_tcv2 = manta_noise_get_texture_v2(fds->fluid);
     float *n_wt_tcw2 = manta_noise_get_texture_w2(fds->fluid);
 
-    int wt_res_old[3];
+    int res_noise[3], res_noise_old[3];
-    manta_noise_get_res(fluid_old, wt_res_old);
+    manta_noise_get_res(fds->fluid, res_noise);
+    manta_noise_get_res(fluid_old, res_noise_old);
 
     for (int z = o_min[2]; z < o_max[2]; z++) {
       for (int y = o_min[1]; y < o_max[1]; y++) {
@@ -257,13 +257,13 @@ void BKE_fluid_reallocate_copy_fluid(FluidDomainSettings *fds,
           if (fds->flags & FLUID_DOMAIN_USE_NOISE) {
             int i, j, k;
             /* old grid index */
-            int xx_o = xo * block_size;
+            int xx_o = xo * block_size[0];
-            int yy_o = yo * block_size;
+            int yy_o = yo * block_size[1];
-            int zz_o = zo * block_size;
+            int zz_o = zo * block_size[2];
             /* new grid index */
-            int xx_n = xn * block_size;
+            int xx_n = xn * block_size[0];
-            int yy_n = yn * block_size;
+            int yy_n = yn * block_size[1];
-            int zz_n = zn * block_size;
+            int zz_n = zn * block_size[2];
 
             /* insert old texture values into new texture grids */
             n_wt_tcu[index_new] = o_wt_tcu[index_old];
@@ -274,13 +274,13 @@ void BKE_fluid_reallocate_copy_fluid(FluidDomainSettings *fds,
             n_wt_tcv2[index_new] = o_wt_tcv2[index_old];
             n_wt_tcw2[index_new] = o_wt_tcw2[index_old];
 
-            for (i = 0; i < block_size; i++) {
+            for (i = 0; i < block_size[0]; i++) {
-              for (j = 0; j < block_size; j++) {
+              for (j = 0; j < block_size[1]; j++) {
-                for (k = 0; k < block_size; k++) {
+                for (k = 0; k < block_size[2]; k++) {
                   int big_index_old = manta_get_index(
-                      xx_o + i, wt_res_old[0], yy_o + j, wt_res_old[1], zz_o + k);
+                      xx_o + i, res_noise_old[0], yy_o + j, res_noise_old[1], zz_o + k);
                   int big_index_new = manta_get_index(
-                      xx_n + i, fds->res_noise[0], yy_n + j, fds->res_noise[1], zz_n + k);
+                      xx_n + i, res_noise[0], yy_n + j, res_noise[1], zz_n + k);
                   /* copy data */
                   n_wt_dens[big_index_new] = o_wt_dens[big_index_old];
                   if (n_wt_flame && o_wt_flame) {
@@ -455,27 +455,32 @@ static void manta_set_domain_from_mesh(FluidDomainSettings *fds,
     return;
   }
 
+  const bool is_2D = (fds->solver_res == FLUID_DOMAIN_DIMENSION_2D);
+  const bool is_axis_X = (fds->slice_axis == SLICE_AXIS_X);
+  const bool is_axis_Y = (fds->slice_axis == SLICE_AXIS_Y);
+  const bool is_axis_Z = (fds->slice_axis == SLICE_AXIS_Z);
+
   /* Define grid resolutions from longest domain side. */
   if (size[0] >= MAX2(size[1], size[2])) {
     scale = res / size[0];
     fds->scale = size[0] / fabsf(ob->scale[0]);
-    fds->base_res[0] = res;
+    fds->base_res[0] = (is_2D && is_axis_X) ? 1 : res;
-    fds->base_res[1] = max_ii((int)(size[1] * scale + 0.5f), 4);
+    fds->base_res[1] = (is_2D && is_axis_Y) ? 1 : max_ii((int)(size[1] * scale + 0.5f), 4);
-    fds->base_res[2] = max_ii((int)(size[2] * scale + 0.5f), 4);
+    fds->base_res[2] = (is_2D && is_axis_Z) ? 1 : max_ii((int)(size[2] * scale + 0.5f), 4);
   }
   else if (size[1] >= MAX2(size[0], size[2])) {
     scale = res / size[1];
     fds->scale = size[1] / fabsf(ob->scale[1]);
-    fds->base_res[0] = max_ii((int)(size[0] * scale + 0.5f), 4);
+    fds->base_res[0] = (is_2D && is_axis_X) ? 1 : max_ii((int)(size[0] * scale + 0.5f), 4);
-    fds->base_res[1] = res;
+    fds->base_res[1] = (is_2D && is_axis_Y) ? 1 : res;
-    fds->base_res[2] = max_ii((int)(size[2] * scale + 0.5f), 4);
+    fds->base_res[2] = (is_2D && is_axis_Z) ? 1 : max_ii((int)(size[2] * scale + 0.5f), 4);
   }
   else {
     scale = res / size[2];
     fds->scale = size[2] / fabsf(ob->scale[2]);
-    fds->base_res[0] = max_ii((int)(size[0] * scale + 0.5f), 4);
+    fds->base_res[0] = (is_2D && is_axis_X) ? 1 : max_ii((int)(size[0] * scale + 0.5f), 4);
-    fds->base_res[1] = max_ii((int)(size[1] * scale + 0.5f), 4);
+    fds->base_res[1] = (is_2D && is_axis_Y) ? 1 : max_ii((int)(size[1] * scale + 0.5f), 4);
-    fds->base_res[2] = res;
+    fds->base_res[2] = (is_2D && is_axis_Z) ? 1 : res;
   }
 
   /* Set cell size. */
@@ -2270,7 +2275,10 @@ static void adaptive_domain_adjust(
   fds->p1[2] = fds->p0[2] + fds->cell_size[2] * fds->base_res[2];
 
   /* adjust domain resolution */
-  const int block_size = fds->noise_scale;
+  int block_size[3] = {fds->noise_scale, fds->noise_scale, fds->noise_scale};
+  if (fds->solver_res == FLUID_DOMAIN_DIMENSION_2D) {
+    block_size[fds->slice_axis - 1] = 1;
+  }
   int min[3] = {32767, 32767, 32767}, max[3] = {-32767, -32767, -32767}, res[3];
   int total_cells = 1, res_changed = 0, shift_changed = 0;
   float min_vel[3], max_vel[3];
@@ -2282,10 +2290,10 @@ static void adaptive_domain_adjust(
   float *vx = manta_get_velocity_x(fds->fluid);
   float *vy = manta_get_velocity_y(fds->fluid);
   float *vz = manta_get_velocity_z(fds->fluid);
-  int wt_res[3];
 
+  int res_noise[3];
   if (fds->flags & FLUID_DOMAIN_USE_NOISE && fds->fluid) {
-    manta_noise_get_res(fds->fluid, wt_res);
+    manta_noise_get_res(fds->fluid, res_noise);
   }
 
   INIT_MINMAX(min_vel, max_vel);
@@ -2317,14 +2325,15 @@ static void adaptive_domain_adjust(
         if (max_den < fds->adapt_threshold && fds->flags & FLUID_DOMAIN_USE_NOISE && fds->fluid) {
           int i, j, k;
           /* high res grid index */
-          int xx = (x - fds->res_min[0]) * block_size;
+          int xx = (x - fds->res_min[0]) * block_size[0];
-          int yy = (y - fds->res_min[1]) * block_size;
+          int yy = (y - fds->res_min[1]) * block_size[1];
-          int zz = (z - fds->res_min[2]) * block_size;
+          int zz = (z - fds->res_min[2]) * block_size[2];
 
-          for (i = 0; i < block_size; i++) {
+          for (i = 0; i < block_size[0]; i++) {
-            for (j = 0; j < block_size; j++) {
+            for (j = 0; j < block_size[1]; j++) {
-              for (k = 0; k < block_size; k++) {
+              for (k = 0; k < block_size[2]; k++) {
-                int big_index = manta_get_index(xx + i, wt_res[0], yy + j, wt_res[1], zz + k);
+                int big_index = manta_get_index(
+                    xx + i, res_noise[0], yy + j, res_noise[1], zz + k);
                 float den = (bigfuel) ? MAX2(bigdensity[big_index], bigfuel[big_index]) :
                                         bigdensity[big_index];
                 if (den > max_den) {
@@ -4708,6 +4717,16 @@ void BKE_fluid_effector_type_set(Object *UNUSED(object), FluidEffectorSettings *
   settings->type = type;
 }
 
+void BKE_fluid_domain_solver_res_set(Object *UNUSED(object),
+                                     FluidDomainSettings *settings,
+                                     int res)
+{
+  if (res == FLUID_DOMAIN_DIMENSION_2D && settings->slice_axis == SLICE_AXIS_AUTO) {
+    settings->slice_axis = SLICE_AXIS_X;
+  }
+  settings->solver_res = res;
+}
+
 void BKE_fluid_fields_sanitize(FluidDomainSettings *settings)
 {
   /* Based on the domain type, certain fields are defaulted accordingly if the selected field

source/blender/blenkernel/intern/particle_system.c

@@ -4379,6 +4379,21 @@ static void particles_fluid_step(ParticleSimulationData *sim,
           const float posParticle[3] = {posX, posY, posZ};
           copy_v3_v3(pa->state.co, posParticle);
 
+          /* Adjust particle position for 2d representation. */
+          if (fds->solver_res == FLUID_DOMAIN_DIMENSION_2D) {
+            if (fds->slice_axis == SLICE_AXIS_X) {
+              float tmp = pa->state.co[1];
+              pa->state.co[1] = pa->state.co[0];
+              pa->state.co[0] = pa->state.co[2];
+              pa->state.co[2] = tmp;
+            }
+            if (fds->slice_axis == SLICE_AXIS_Y) {
+              float tmp = pa->state.co[1];
+              pa->state.co[1] = pa->state.co[2];
+              pa->state.co[2] = tmp;
+            }
+          }
+
           /* Normalize to unit cube around 0. */
           float resDomain[3] = {resX, resY, resZ};
           mul_v3_fl(resDomain, 0.5f);
@@ -4412,6 +4427,21 @@ static void particles_fluid_step(ParticleSimulationData *sim,
           const float velParticle[3] = {velX, velY, velZ};
           copy_v3_v3(pa->state.vel, velParticle);
           mul_v3_fl(pa->state.vel, fds->dx);
+
+          /* Adjust particle velocity for 2d representation. */
+          if (fds->solver_res == FLUID_DOMAIN_DIMENSION_2D) {
+            if (fds->slice_axis == SLICE_AXIS_X) {
+              float tmp = pa->state.vel[1];
+              pa->state.vel[0] = pa->state.vel[2];
+              pa->state.vel[1] = pa->state.vel[0];
+              pa->state.vel[2] = tmp;
+            }
+            else if (fds->slice_axis == SLICE_AXIS_Y) {
+              float tmp = pa->state.vel[1];
+              pa->state.vel[1] = pa->state.vel[2];
+              pa->state.vel[2] = tmp;
+            }
+          }
 #  if 0
           /* Debugging: Print particle velocity. */
           printf("pa->state.vel[0]: %f, pa->state.vel[1]: %f, pa->state.vel[2]: %f\n",

source/blender/draw/engines/overlay/overlay_extra.c

@@ -1392,15 +1392,20 @@ static void OVERLAY_volume_extra(OVERLAY_ExtraCallBuffers *cb,
   const bool color_range = (fds->gridlines_color_field == FLUID_GRIDLINE_COLOR_TYPE_RANGE &&
                             fds->use_coba && fds->coba_field != FLUID_DOMAIN_FIELD_FLAGS);
 
+  const bool is_2D = (fds->solver_res == FLUID_DOMAIN_DIMENSION_2D);
+  const bool is_axis_X = (fds->slice_axis == SLICE_AXIS_X);
+  const bool is_axis_Y = (fds->slice_axis == SLICE_AXIS_Y);
+  const bool is_axis_Z = (fds->slice_axis == SLICE_AXIS_Z);
+
   /* Small cube showing voxel size. */
   {
     float min[3];
     madd_v3fl_v3fl_v3fl_v3i(min, fds->p0, fds->cell_size, fds->res_min);
     float voxel_cubemat[4][4] = {{0.0f}};
     /* scale small cube to voxel size */
-    voxel_cubemat[0][0] = fds->cell_size[0] / 2.0f;
+    voxel_cubemat[0][0] = (is_2D && is_axis_X) ? 0.0f : (fds->cell_size[0] / 2.0f);
-    voxel_cubemat[1][1] = fds->cell_size[1] / 2.0f;
+    voxel_cubemat[1][1] = (is_2D && is_axis_Y) ? 0.0f : (fds->cell_size[1] / 2.0f);
-    voxel_cubemat[2][2] = fds->cell_size[2] / 2.0f;
+    voxel_cubemat[2][2] = (is_2D && is_axis_Z) ? 0.0f : (fds->cell_size[2] / 2.0f);
     voxel_cubemat[3][3] = 1.0f;
     /* translate small cube to corner */
     copy_v3_v3(voxel_cubemat[3], min);

source/blender/draw/engines/workbench/workbench_volume.c

@@ -92,7 +92,8 @@ static void workbench_volume_modifier_cache_populate(WORKBENCH_Data *vedata,
     return;
   }
 
-  const bool use_slice = (fds->axis_slice_method == AXIS_SLICE_SINGLE);
+  const bool use_slice = (fds->axis_slice_method == AXIS_SLICE_SINGLE) ||
+                         (fds->solver_res == FLUID_DOMAIN_DIMENSION_2D);
   const bool show_phi = ELEM(fds->coba_field,
                              FLUID_DOMAIN_FIELD_PHI,
                              FLUID_DOMAIN_FIELD_PHI_IN,

source/blender/draw/intern/draw_fluid.c

@@ -327,7 +327,13 @@ static GPUTexture *create_field_texture(FluidDomainSettings *fds, bool single_pr
 
 static GPUTexture *create_density_texture(FluidDomainSettings *fds, int highres)
 {
-  int *dim = (highres) ? fds->res_noise : fds->res;
+  int res[3];
+  if (highres) {
+    manta_noise_get_res(fds->fluid, res);
+  }
+  else {
+    manta_get_res(fds->fluid, res);
+  }
 
   float *data;
   if (highres) {
@@ -341,7 +347,7 @@ static GPUTexture *create_density_texture(FluidDomainSettings *fds, int highres)
     return NULL;
   }
 
-  GPUTexture *tex = create_volume_texture(dim, GPU_R8, GPU_DATA_FLOAT, data);
+  GPUTexture *tex = create_volume_texture(res, GPU_R8, GPU_DATA_FLOAT, data);
   swizzle_texture_channel_single(tex);
   return tex;
 }
@@ -356,7 +362,15 @@ static GPUTexture *create_color_texture(FluidDomainSettings *fds, int highres)
   }
 
   int cell_count = (highres) ? manta_noise_get_cells(fds->fluid) : fds->total_cells;
-  int *dim = (highres) ? fds->res_noise : fds->res;
+
+  int res[3];
+  if (highres) {
+    manta_noise_get_res(fds->fluid, res);
+  }
+  else {
+    manta_get_res(fds->fluid, res);
+  }
+
   float *data = (float *)MEM_callocN(sizeof(float) * cell_count * 4, "smokeColorTexture");
 
   if (data == NULL) {
@@ -370,7 +384,7 @@ static GPUTexture *create_color_texture(FluidDomainSettings *fds, int highres)
     manta_smoke_get_rgba(fds->fluid, data, 0);
   }
 
-  GPUTexture *tex = create_volume_texture(dim, GPU_RGBA8, GPU_DATA_FLOAT, data);
+  GPUTexture *tex = create_volume_texture(res, GPU_RGBA8, GPU_DATA_FLOAT, data);
 
   MEM_freeN(data);
 
@@ -382,7 +396,14 @@ static GPUTexture *create_flame_texture(FluidDomainSettings *fds, int highres)
   float *source = NULL;
   const bool has_fuel = (highres) ? manta_noise_has_fuel(fds->fluid) :
                                     manta_smoke_has_fuel(fds->fluid);
-  int *dim = (highres) ? fds->res_noise : fds->res;
+
+  int res[3];
+  if (highres) {
+    manta_noise_get_res(fds->fluid, res);
+  }
+  else {
+    manta_get_res(fds->fluid, res);
+  }
 
   if (!has_fuel) {
     return NULL;
@@ -395,7 +416,7 @@ static GPUTexture *create_flame_texture(FluidDomainSettings *fds, int highres)
     source = manta_smoke_get_flame(fds->fluid);
   }
 
-  GPUTexture *tex = create_volume_texture(dim, GPU_R8, GPU_DATA_FLOAT, source);
+  GPUTexture *tex = create_volume_texture(res, GPU_R8, GPU_DATA_FLOAT, source);
   swizzle_texture_channel_single(tex);
   return tex;
 }

source/blender/makesdna/DNA_fluid_defaults.h

@@ -99,7 +99,6 @@
     .noise_strength = 1.0f, \
     .noise_pos_scale = 2.0f, \
     .noise_time_anim = 0.1f, \
-    .res_noise = {0, 0, 0}, \
     .noise_scale = 2, \
     .particle_randomness = 0.1f, \
     .particle_number = 2, \

source/blender/makesdna/DNA_fluid_types.h

@@ -198,6 +198,12 @@ enum {
   FLUID_DOMAIN_TYPE_LIQUID = 1,
 };
 
+/* Fluid domain dimension. */
+enum {
+  FLUID_DOMAIN_DIMENSION_2D = 2,
+  FLUID_DOMAIN_DIMENSION_3D = 3,
+};
+
 /* Mesh levelset generator types. */
 enum {
   FLUID_DOMAIN_MESH_IMPROVED = 0,
@@ -573,9 +579,7 @@ typedef struct FluidDomainSettings {
   float noise_strength;
   float noise_pos_scale;
   float noise_time_anim;
-  int res_noise[3];
   int noise_scale;
-  char _pad3[4]; /* Unused. */
 
   /* Liquid domain options. */
   float particle_randomness;
@@ -589,11 +593,11 @@ typedef struct FluidDomainSettings {
   float flip_ratio;
   int sys_particle_maximum;
   short simulation_method;
-  char _pad4[6];
+  char _pad3[6];
 
   /* Viscosity options. */
   float viscosity_value;
-  char _pad5[4];
+  char _pad4[4];
 
   /* Diffusion options. */
   float surface_tension;
@@ -609,7 +613,7 @@ typedef struct FluidDomainSettings {
   int mesh_scale;
   int totvert;
   short mesh_generator;
-  char _pad6[6]; /* Unused. */
+  char _pad5[6]; /* Unused. */
 
   /* Secondary particle options. */
   int particle_type;
@@ -630,7 +634,7 @@ typedef struct FluidDomainSettings {
   int sndparticle_update_radius;
   char sndparticle_boundary;
   char sndparticle_combined_export;
-  char _pad7[6]; /* Unused. */
+  char _pad6[6]; /* Unused. */
 
   /* Fluid guiding options. */
   float guide_alpha;      /* Guiding weight scalar (determines strength). */
@@ -638,7 +642,7 @@ typedef struct FluidDomainSettings {
   float guide_vel_factor; /* Multiply guiding velocity by this factor. */
   int guide_res[3];       /* Res for velocity guide grids - independent from base res. */
   short guide_source;
-  char _pad8[2]; /* Unused. */
+  char _pad7[2]; /* Unused. */
 
   /* Cache options. */
   int cache_frame_start;
@@ -658,7 +662,7 @@ typedef struct FluidDomainSettings {
   char error[64]; /* Bake error description. */
   short cache_type;
   char cache_id[4]; /* Run-time only */
-  char _pad9[2];    /* Unused. */
+  char _pad8[2];    /* Unused. */
 
   /* Time options. */
   float dt;
@@ -693,19 +697,19 @@ typedef struct FluidDomainSettings {
   char interp_method;
   char gridlines_color_field; /* Simulation field used to color map onto gridlines. */
   char gridlines_cell_filter;
-  char _pad10[7]; /* Unused. */
+  char _pad9[7]; /* Unused. */
 
   /* OpenVDB cache options. */
   int openvdb_compression;
   float clipping;
   char openvdb_data_depth;
-  char _pad11[7]; /* Unused. */
+  char _pad10[7]; /* Unused. */
 
   /* -- Deprecated / unsed options (below). -- */
 
   /* View options. */
   int viewsettings;
-  char _pad12[4]; /* Unused. */
+  char _pad11[4]; /* Unused. */
 
   /* Pointcache options. */
   /* Smoke uses only one cache from now on (index [0]), but keeping the array for now for reading
@@ -715,7 +719,7 @@ typedef struct FluidDomainSettings {
   int cache_comp;
   int cache_high_comp;
   char cache_file_format;
-  char _pad13[7]; /* Unused. */
+  char _pad12[7]; /* Unused. */
 
 } FluidDomainSettings;
 

source/blender/makesrna/intern/rna_fluid.c

@@ -220,6 +220,16 @@ static void rna_Fluid_reset_dependency(Main *bmain, Scene *scene, PointerRNA *pt
   rna_Fluid_dependency_update(bmain, scene, ptr);
 }
 
+static void rna_Fluid_slice_axis_reset(Main *bmain, Scene *scene, PointerRNA *ptr)
+{
+#  ifdef WITH_FLUID
+  FluidDomainSettings *settings = (FluidDomainSettings *)ptr->data;
+  if (settings->solver_res == FLUID_DOMAIN_DIMENSION_2D) {
+    rna_Fluid_domain_data_reset(bmain, scene, ptr);
+  }
+#  endif
+}
+
 static void rna_Fluid_parts_create(Main *bmain,
                                    PointerRNA *ptr,
                                    const char *pset_name,
@@ -863,6 +873,60 @@ static const EnumPropertyItem *rna_Fluid_data_depth_itemf(bContext *UNUSED(C),
   return item;
 }
 
+static const EnumPropertyItem *rna_Fluid_slice_axis_itemf(bContext *UNUSED(C),
+                                                          PointerRNA *ptr,
+                                                          PropertyRNA *UNUSED(prop),
+                                                          bool *r_free)
+{
+  FluidDomainSettings *settings = (FluidDomainSettings *)ptr->data;
+
+  EnumPropertyItem *item = NULL;
+  EnumPropertyItem tmp = {0, "", 0, "", ""};
+  int totitem = 0;
+
+  if (settings->solver_res == FLUID_DOMAIN_DIMENSION_3D) {
+    tmp.value = SLICE_AXIS_AUTO;
+    tmp.identifier = "AUTO";
+    tmp.icon = 0;
+    tmp.name = "Auto";
+    tmp.description = "Adjust slice direction according to the view direction";
+    RNA_enum_item_add(&item, &totitem, &tmp);
+  }
+
+  tmp.value = SLICE_AXIS_X;
+  tmp.identifier = "X";
+  tmp.icon = 0;
+  tmp.name = "X";
+  tmp.description = "Slice along the X axis";
+  RNA_enum_item_add(&item, &totitem, &tmp);
+
+  tmp.value = SLICE_AXIS_Y;
+  tmp.identifier = "Y";
+  tmp.icon = 0;
+  tmp.name = "Y";
+  tmp.description = "Slice along the Y axis";
+  RNA_enum_item_add(&item, &totitem, &tmp);
+
+  tmp.value = SLICE_AXIS_Z;
+  tmp.identifier = "Z";
+  tmp.icon = 0;
+  tmp.name = "Z";
+  tmp.description = "Slice along the Z axis";
+  RNA_enum_item_add(&item, &totitem, &tmp);
+
+  RNA_enum_item_end(&item, &totitem);
+  *r_free = true;
+
+  return item;
+}
+
+static void rna_Fluid_solver_res_set(struct PointerRNA *ptr, int value)
+{
+  FluidDomainSettings *settings = (FluidDomainSettings *)ptr->data;
+  Object *ob = (Object *)ptr->owner_id;
+  BKE_fluid_domain_solver_res_set(ob, settings, value);
+}
+
 static void rna_Fluid_domaintype_set(struct PointerRNA *ptr, int value)
 {
   FluidDomainSettings *settings = (FluidDomainSettings *)ptr->data;
@@ -1268,6 +1332,12 @@ static void rna_def_fluid_domain_settings(BlenderRNA *brna)
       {FLUID_DOMAIN_TYPE_LIQUID, "LIQUID", 0, "Liquid", "Create domain for liquids"},
       {0, NULL, 0, NULL, NULL}};
 
+  static EnumPropertyItem solver_res_items[] = {
+      {FLUID_DOMAIN_DIMENSION_2D, "2D", 0, "2D", "Create 2D domain"},
+      {FLUID_DOMAIN_DIMENSION_3D, "3D", 0, "3D", "Create 3D domain"},
+      {0, NULL, 0, NULL, NULL},
+  };
+
   static const EnumPropertyItem prop_compression_items[] = {
       {VDB_COMPRESSION_ZIP, "ZIP", 0, "Zip", "Effective but slow compression"},
 #  ifdef WITH_OPENVDB_BLOSC
@@ -1351,15 +1421,9 @@ static void rna_def_fluid_domain_settings(BlenderRNA *brna)
       {0, NULL, 0, NULL, NULL},
   };
 
+  /* Axis options are generated dynamically based on domain dimension (2D or 3D). */
   static const EnumPropertyItem axis_slice_position_items[] = {
-      {SLICE_AXIS_AUTO,
+      {0, "NONE", 0, "", ""},
-       "AUTO",
-       0,
-       "Auto",
-       "Adjust slice direction according to the view direction"},
-      {SLICE_AXIS_X, "X", 0, "X", "Slice along the X axis"},
-      {SLICE_AXIS_Y, "Y", 0, "Y", "Slice along the Y axis"},
-      {SLICE_AXIS_Z, "Z", 0, "Z", "Slice along the Z axis"},
       {0, NULL, 0, NULL, NULL},
   };
 
@@ -1670,6 +1734,13 @@ static void rna_def_fluid_domain_settings(BlenderRNA *brna)
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
   RNA_def_property_update(prop, NC_OBJECT | ND_DRAW, "rna_Fluid_flip_parts_update");
 
+  prop = RNA_def_property(srna, "solver_res", PROP_ENUM, PROP_NONE);
+  RNA_def_property_enum_items(prop, solver_res_items);
+  RNA_def_property_enum_funcs(prop, NULL, "rna_Fluid_solver_res_set", NULL);
+  RNA_def_property_ui_text(prop, "Dimension", "Change the solver resolution");
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_update(prop, NC_OBJECT | ND_DRAW, "rna_Fluid_datacache_reset");
+
   prop = RNA_def_property(srna, "delete_in_obstacle", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, NULL, "flags", FLUID_DOMAIN_DELETE_IN_OBSTACLE);
   RNA_def_property_ui_text(prop, "Clear In Obstacle", "Delete fluid inside obstacles");
@@ -2518,8 +2589,9 @@ static void rna_def_fluid_domain_settings(BlenderRNA *brna)
   prop = RNA_def_property(srna, "slice_axis", PROP_ENUM, PROP_NONE);
   RNA_def_property_enum_sdna(prop, NULL, "slice_axis");
   RNA_def_property_enum_items(prop, axis_slice_position_items);
+  RNA_def_property_enum_funcs(prop, NULL, NULL, "rna_Fluid_slice_axis_itemf");
   RNA_def_property_ui_text(prop, "Axis", "");
-  RNA_def_property_update(prop, NC_OBJECT | ND_DRAW, NULL);
+  RNA_def_property_update(prop, NC_OBJECT | ND_DRAW, "rna_Fluid_slice_axis_reset");
 
   prop = RNA_def_property(srna, "slice_per_voxel", PROP_FLOAT, PROP_NONE);
   RNA_def_property_float_sdna(prop, NULL, "slice_per_voxel");