Fluid: Refactored fluid gravity settings

Refactored setup that converts from Blender to Mantaflow units.

1 files changed, 37 insertions, 17 deletions

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\