[Bf-blender-cvs] [4edaa796d33] blender-v2.91-release: Fluid: Revert changes from T82488

[Sebastián Barschkis]

Commit: 4edaa796d3396fcadc73596e6c6232a498a12e3c
Author: Sebastián Barschkis
Date:   Wed Nov 18 15:38:00 2020 +0100
Branches: blender-v2.91-release
https://developer.blender.org/rB4edaa796d3396fcadc73596e6c6232a498a12e3c

Fluid: Revert changes from T82488

Scaling of forces needs more work. Before making changes to them it would be nice to have a setup, that works physically correct across multiple modifiers (cloth, rigid bodies, fluid).

This will be a to do for 2.92.

===================================================================

M	intern/mantaflow/intern/strings/fluid_script.h
M	source/blender/blenkernel/intern/fluid.c

===================================================================

diff --git a/intern/mantaflow/intern/strings/fluid_script.h b/intern/mantaflow/intern/strings/fluid_script.h
index c416a84c71c..5f17c1f4b44 100644
--- a/intern/mantaflow/intern/strings/fluid_script.h
+++ b/intern/mantaflow/intern/strings/fluid_script.h
@@ -122,6 +122,7 @@ timePerFrame_s$ID$ = $TIME_PER_FRAME$\n\
 # In Blender fluid.c: frame_length = DT_DEFAULT * (25.0 / fps) * time_scale\n\
 # with DT_DEFAULT = 0.1\n\
 frameLength_s$ID$ = $FRAME_LENGTH$\n\
+frameLengthUnscaled_s$ID$ = frameLength_s$ID$ / timeScale_s$ID$\n\
 frameLengthRaw_s$ID$ = 0.1 * 25 # dt = 0.1 at 25 fps\n\
 \n\
 dt0_s$ID$          = $DT$\n\
@@ -148,9 +149,15 @@ mantaMsg('1 Blender length unit is ' + str(ratioResToBLength_s$ID$) + ' Mantaflo
 ratioBTimeToTimestep_s$ID$ = float(1) / float(frameLengthRaw_s$ID$) # the time within 1 blender time unit, see also fluid.c\n\
 mantaMsg('1 Blender time unit is ' + str(ratioBTimeToTimestep_s$ID$) + ' Mantaflow time units long.')\n\
 \n\
+ratioFrameToFramelength_s$ID$ = float(1) / float(frameLengthUnscaled_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$ID$ * (ratioBTimeToTimestep_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\
 gravity_s$ID$ *= scaleAcceleration_s$ID$ # scale from world acceleration to cell based acceleration\n\
 \n\
 # OpenVDB options\n\
@@ -380,6 +387,9 @@ def fluid_pre_step_$ID$():\n\
         interpolateMACGrid(source=guidevel_sg$ID$, target=velT_s$ID$)\n\
         velT_s$ID$.multConst(vec3(gamma_sg$ID$))\n\
     \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\
diff --git a/source/blender/blenkernel/intern/fluid.c b/source/blender/blenkernel/intern/fluid.c
index b9f201d8ada..452e01363ab 100644
--- a/source/blender/blenkernel/intern/fluid.c
+++ b/source/blender/blenkernel/intern/fluid.c
@@ -3196,6 +3196,8 @@ static void update_effectors_task_cb(void *__restrict userdata,
       mul_v3_fl(retvel, mag);
 
       /* Copy computed force to fluid solver forces. */
+      mul_v3_fl(retvel, 0.2f);     /* Factor from 0e6820cc5d62. */
+      CLAMP3(retvel, -1.0f, 1.0f); /* Restrict forces to +-1 interval. */
       data->force_x[index] = retvel[0];
       data->force_y[index] = retvel[1];
       data->force_z[index] = retvel[2];