8 files changed, 86 insertions, 3 deletions

diff --git a/release/scripts/startup/bl_ui/space_dopesheet.py b/release/scripts/startup/bl_ui/space_dopesheet.py
index 6e5eba7b734..3c90e0c96cc 100644
--- a/release/scripts/startup/bl_ui/space_dopesheet.py
+++ b/release/scripts/startup/bl_ui/space_dopesheet.py
@@ -556,6 +556,8 @@ class DopesheetActionPanelBase:
         row.prop(action, "frame_start", text="Start")
         row.prop(action, "frame_end", text="End")
 
+        col.prop(action, "use_cyclic")
+
 
 class DOPESHEET_PT_action(DopesheetActionPanelBase, Panel):
     bl_space_type = 'DOPESHEET_EDITOR'
diff --git a/source/blender/blenkernel/BKE_action.h b/source/blender/blenkernel/BKE_action.h
index 6d457ed32f0..b5e94793658 100644
--- a/source/blender/blenkernel/BKE_action.h
+++ b/source/blender/blenkernel/BKE_action.h
@@ -98,6 +98,9 @@ void BKE_action_get_frame_range(const struct bAction *act, float *r_start, float
 /* Does action have any motion data at all? */
 bool action_has_motion(const struct bAction *act);
 
+/* Is the action configured as cyclic. */
+bool BKE_action_is_cyclic(const struct bAction *act);
+
 /* Action Groups API ----------------- */
 
 /* Get the active action-group for an Action */
diff --git a/source/blender/blenkernel/intern/action.c b/source/blender/blenkernel/intern/action.c
index 47db5183e76..408a0b3065e 100644
--- a/source/blender/blenkernel/intern/action.c
+++ b/source/blender/blenkernel/intern/action.c
@@ -1591,6 +1591,12 @@ void BKE_action_get_frame_range(const struct bAction *act, float *r_start, float
   }
 }
 
+/* Is the action configured as cyclic. */
+bool BKE_action_is_cyclic(const struct bAction *act)
+{
+  return act && (act->flag & ACT_FRAME_RANGE) && (act->flag & ACT_CYCLIC);
+}
+
 /* Return flags indicating which transforms the given object/posechannel has
  * - if 'curves' is provided, a list of links to these curves are also returned
  */
diff --git a/source/blender/blenkernel/intern/nla.c b/source/blender/blenkernel/intern/nla.c
index 0666c1dfc53..8f2a60358e7 100644
--- a/source/blender/blenkernel/intern/nla.c
+++ b/source/blender/blenkernel/intern/nla.c
@@ -395,6 +395,11 @@ NlaStrip *BKE_nlastrip_new(bAction *act)
     strip->flag &= ~NLASTRIP_FLAG_SYNC_LENGTH;
   }
 
+  /* Enable cyclic time for known cyclic actions. */
+  if (BKE_action_is_cyclic(act)) {
+    strip->flag |= NLASTRIP_FLAG_USR_TIME_CYCLIC;
+  }
+
   /* assign the action reference */
   strip->act = act;
   id_us_plus(&act->id);
diff --git a/source/blender/editors/animation/keyframing.c b/source/blender/editors/animation/keyframing.c
index 0a9f1a36a28..95d1ca1e7a6 100644
--- a/source/blender/editors/animation/keyframing.c
+++ b/source/blender/editors/animation/keyframing.c
@@ -35,6 +35,7 @@
 
 #include "BLT_translation.h"
 
+#include "DNA_action_types.h"
 #include "DNA_anim_types.h"
 #include "DNA_armature_types.h"
 #include "DNA_constraint_types.h"
@@ -375,6 +376,43 @@ static eFCU_Cycle_Type remap_cyclic_keyframe_location(FCurve *fcu, float *px, fl
   return type;
 }
 
+/* Used to make curves newly added to a cyclic Action cycle with the correct period. */
+static void make_new_fcurve_cyclic(const bAction *act, FCurve *fcu)
+{
+  /* The curve must contain one (newly-added) keyframe. */
+  if (fcu->totvert != 1 || !fcu->bezt) {
+    return;
+  }
+
+  const float period = act->frame_end - act->frame_start;
+
+  if (period < 0.1f) {
+    return;
+  }
+
+  /* Move the keyframe into the range. */
+  const float frame_offset = fcu->bezt[0].vec[1][0] - act->frame_start;
+  const float fix = floorf(frame_offset / period) * period;
+
+  fcu->bezt[0].vec[0][0] -= fix;
+  fcu->bezt[0].vec[1][0] -= fix;
+  fcu->bezt[0].vec[2][0] -= fix;
+
+  /* Duplicate and offset the keyframe. */
+  fcu->bezt = MEM_reallocN(fcu->bezt, sizeof(BezTriple) * 2);
+  fcu->totvert = 2;
+
+  fcu->bezt[1] = fcu->bezt[0];
+  fcu->bezt[1].vec[0][0] += period;
+  fcu->bezt[1].vec[1][0] += period;
+  fcu->bezt[1].vec[2][0] += period;
+
+  /* Add the cycles modifier. */
+  if (!fcu->modifiers.first) {
+    add_fmodifier(&fcu->modifiers, FMODIFIER_TYPE_CYCLES, fcu);
+  }
+}
+
 /* -------------- BezTriple Insertion -------------------- */
 
 /* Change the Y position of a keyframe to match the input, adjusting handles. */
@@ -1352,8 +1390,10 @@ static bool insert_keyframe_fcurve_value(Main *bmain,
 
   /* we may not have a F-Curve when we're replacing only... */
   if (fcu) {
+    const bool is_new_curve = (fcu->totvert == 0);
+
     /* set color mode if the F-Curve is new (i.e. without any keyframes) */
-    if ((fcu->totvert == 0) && (flag & INSERTKEY_XYZ2RGB)) {
+    if (is_new_curve && (flag & INSERTKEY_XYZ2RGB)) {
       /* for Loc/Rot/Scale and also Color F-Curves, the color of the F-Curve in the Graph Editor,
        * is determined by the array index for the F-Curve
        */
@@ -1366,12 +1406,26 @@ static bool insert_keyframe_fcurve_value(Main *bmain,
       }
     }
 
+    /* If the curve has only one key, make it cyclic if appropriate. */
+    const bool is_cyclic_action = (flag & INSERTKEY_CYCLE_AWARE) && BKE_action_is_cyclic(act);
+
+    if (is_cyclic_action && fcu->totvert == 1) {
+      make_new_fcurve_cyclic(act, fcu);
+    }
+
     /* update F-Curve flags to ensure proper behavior for property type */
     update_autoflags_fcurve_direct(fcu, prop);
 
     /* insert keyframe */
-    return insert_keyframe_value(
+    const bool success = insert_keyframe_value(
         reports, ptr, prop, fcu, anim_eval_context, curval, keytype, flag);
+
+    /* If the curve is new, make it cyclic if appropriate. */
+    if (is_cyclic_action && is_new_curve) {
+      make_new_fcurve_cyclic(act, fcu);
+    }
+
+    return success;
   }
 
   return false;
diff --git a/source/blender/makesdna/DNA_action_types.h b/source/blender/makesdna/DNA_action_types.h
index 9d1de4c0c36..8e7551e1703 100644
--- a/source/blender/makesdna/DNA_action_types.h
+++ b/source/blender/makesdna/DNA_action_types.h
@@ -701,6 +701,8 @@ typedef enum eAction_Flags {
   /* ACT_DISABLED = (1 << 11), */  /* UNUSED */
   /** The action has a manually set intended playback frame range. */
   ACT_FRAME_RANGE = (1 << 12),
+  /** The action is intended to be a cycle (requires ACT_FRAME_RANGE). */
+  ACT_CYCLIC = (1 << 13),
 } eAction_Flags;
 
 /* ************************************************ */
diff --git a/source/blender/makesrna/intern/rna_action.c b/source/blender/makesrna/intern/rna_action.c
index db2c415c918..96e37dfebbb 100644
--- a/source/blender/makesrna/intern/rna_action.c
+++ b/source/blender/makesrna/intern/rna_action.c
@@ -893,6 +893,16 @@ static void rna_def_action(BlenderRNA *brna)
       "(this range is used by some tools, but does not affect animation evaluation)");
   RNA_def_property_update(prop, NC_ANIMATION | ND_ANIMCHAN | NA_EDITED, NULL);
 
+  prop = RNA_def_property(srna, "use_cyclic", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", ACT_CYCLIC);
+  RNA_def_property_ui_text(
+      prop,
+      "Cyclic Animation",
+      "The action is intended to be used as a cycle looping over its manually set "
+      "playback frame range (enabling this doesn't automatically make it loop)");
+  RNA_def_property_update(prop, NC_ANIMATION | ND_ANIMCHAN | NA_EDITED, NULL);
+
   prop = RNA_def_property(srna, "frame_start", PROP_FLOAT, PROP_TIME);
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
   RNA_def_property_float_sdna(prop, NULL, "frame_start");
diff --git a/source/blender/makesrna/intern/rna_scene.c b/source/blender/makesrna/intern/rna_scene.c
index c69a69290f9..d05f2a13c4b 100644
--- a/source/blender/makesrna/intern/rna_scene.c
+++ b/source/blender/makesrna/intern/rna_scene.c
@@ -3425,7 +3425,8 @@ static void rna_def_tool_settings(BlenderRNA *brna)
       prop,
       "Cycle-Aware Keying",
       "For channels with cyclic extrapolation, keyframe insertion is automatically "
-      "remapped inside the cycle time range, and keeps ends in sync");
+      "remapped inside the cycle time range, and keeps ends in sync. Curves newly added to "
+      "actions with a Manual Frame Range and Cyclic Animation are automatically made cyclic");
 
   /* Keyframing */
   prop = RNA_def_property(srna, "keyframe_type", PROP_ENUM, PROP_NONE);