Fluids: improve subframe handling

Reviewers: sebbas

Differential Revision: https://developer.blender.org/D7256

1 files changed, 15 insertions, 58 deletions

diff --git a/source/blender/blenkernel/intern/fluid.c b/source/blender/blenkernel/intern/fluid.c
index 75e1dce9958..e8da4385fb9 100644
--- a/source/blender/blenkernel/intern/fluid.c
+++ b/source/blender/blenkernel/intern/fluid.c
@@ -1232,52 +1232,31 @@ static void update_obstacles(Depsgraph *depsgraph,
         continue;
       }
 
-      /* Length of one adaptive frame. If using adaptive stepping, length is smaller than actual
-       * frame length */
-      float adaptframe_length = time_per_frame / frame_length;
-      /* Adaptive frame length as percentage */
-      CLAMP(adaptframe_length, 0.0f, 1.0f);
-
-      /* More splitting because of emission subframe: If no subframes present, sample_size is 1. */
-      float sample_size = 1.0f / (float)(subframes + 1);
-
       /* First frame cannot have any subframes because there is (obviously) no previous frame from
        * where subframes could come from. */
       if (is_first_frame) {
         subframes = 0;
       }
 
-      int subframe;
+      /* More splitting because of emission subframe: If no subframes present, sample_size is 1. */
+      float sample_size = 1.0f / (float)(subframes + 1);
       float subframe_dt = dt * sample_size;
 
       /* Emission loop. When not using subframes this will loop only once. */
-      for (subframe = subframes; subframe >= 0; subframe--) {
+      for (int subframe = 0; subframe <= subframes; subframe++) {
 
         /* Temporary emission map used when subframes are enabled, i.e. at least one subframe. */
         FluidObjectBB bb_temp = {NULL};
 
         /* Set scene time */
         /* Handle emission subframe */
-        if (subframe > 0 && !is_first_frame) {
-          scene->r.subframe = adaptframe_length -
-                              sample_size * (float)(subframe) * (dt / frame_length);
+        if (subframe < subframes || time_per_frame + dt + FLT_EPSILON < frame_length) {
+          scene->r.subframe = (time_per_frame + (subframe + 1.0f) * subframe_dt) / frame_length;
           scene->r.cfra = frame - 1;
         }
-        /* Last frame in this loop (subframe == suframes). Can be real end frame or in between
-         * frames (adaptive frame). */
         else {
-          /* Handle adaptive subframe (ie has subframe fraction). Need to set according scene
-           * subframe parameter. */
-          if (time_per_frame < frame_length) {
-            scene->r.subframe = adaptframe_length;
-            scene->r.cfra = frame - 1;
-          }
-          /* Handle absolute endframe (ie no subframe fraction). Need to set the scene subframe
-           * parameter to 0 and advance current scene frame. */
-          else {
-            scene->r.subframe = 0.0f;
-            scene->r.cfra = frame;
-          }
+          scene->r.subframe = 0.0f;
+          scene->r.cfra = frame;
         }
         /* Sanity check: subframe portion must be between 0 and 1. */
         CLAMP(scene->r.subframe, 0.0f, 1.0f);
@@ -2768,53 +2747,31 @@ static void update_flowsfluids(struct Depsgraph *depsgraph,
         continue;
       }
 
-      /* Length of one adaptive frame. If using adaptive stepping, length is smaller than actual
-       * frame length */
-      float adaptframe_length = time_per_frame / frame_length;
-      /* Adaptive frame length as percentage */
-      CLAMP(adaptframe_length, 0.0f, 1.0f);
-
-      /* More splitting because of emission subframe: If no subframes present, sample_size is 1. */
-      float sample_size = 1.0f / (float)(subframes + 1);
-
       /* First frame cannot have any subframes because there is (obviously) no previous frame from
        * where subframes could come from. */
       if (is_first_frame) {
         subframes = 0;
       }
 
-      int subframe;
+      /* More splitting because of emission subframe: If no subframes present, sample_size is 1. */
+      float sample_size = 1.0f / (float)(subframes + 1);
       float subframe_dt = dt * sample_size;
 
       /* Emission loop. When not using subframes this will loop only once. */
-      for (subframe = subframes; subframe >= 0; subframe--) {
-
+      for (int subframe = 0; subframe <= subframes; subframe++) {
         /* Temporary emission map used when subframes are enabled, i.e. at least one subframe. */
         FluidObjectBB bb_temp = {NULL};
 
         /* Set scene time */
-        /* Handle emission subframe */
-        if (subframe > 0 && !is_first_frame) {
-          scene->r.subframe = adaptframe_length -
-                              sample_size * (float)(subframe) * (dt / frame_length);
+        if (subframe < subframes || time_per_frame + dt + FLT_EPSILON < frame_length) {
+          scene->r.subframe = (time_per_frame + (subframe + 1.0f) * subframe_dt) / frame_length;
           scene->r.cfra = frame - 1;
         }
-        /* Last frame in this loop (subframe == suframes). Can be real end frame or in between
-         * frames (adaptive frame). */
         else {
-          /* Handle adaptive subframe (ie has subframe fraction). Need to set according scene
-           * subframe parameter. */
-          if (time_per_frame < frame_length) {
-            scene->r.subframe = adaptframe_length;
-            scene->r.cfra = frame - 1;
-          }
-          /* Handle absolute endframe (ie no subframe fraction). Need to set the scene subframe
-           * parameter to 0 and advance current scene frame. */
-          else {
-            scene->r.subframe = 0.0f;
-            scene->r.cfra = frame;
-          }
+          scene->r.subframe = 0.0f;
+          scene->r.cfra = frame;
         }
+
         /* Sanity check: subframe portion must be between 0 and 1. */
         CLAMP(scene->r.subframe, 0.0f, 1.0f);
 #  ifdef DEBUG_PRINT