scripts/startup/bl_ui/space_graph.py

@@ -299,6 +299,7 @@ class GRAPH_MT_key_blending(Menu):
         layout.operator("graph.blend_to_neighbor", text="Blend to Neighbor")
         layout.operator("graph.blend_to_default", text="Blend to Default Value")
         layout.operator("graph.ease", text="Ease")
+        layout.operator("graph.blend_offset", text="Blend Offset")
 
 
 class GRAPH_MT_key_smoothing(Menu):

source/blender/editors/animation/keyframes_general.cc

@@ -679,6 +679,31 @@ void ease_fcurve_segment(FCurve *fcu, FCurveSegment *segment, const float factor
 
 /* ---------------- */
 
+void blend_offset_fcurve_segment(FCurve *fcu, FCurveSegment *segment, const float factor)
+{
+  const BezTriple *left_key = fcurve_segment_start_get(fcu, segment->start_index);
+  const BezTriple *right_key = fcurve_segment_end_get(fcu, segment->start_index + segment->length);
+
+  float y_delta;
+
+  if (factor > 0) {
+    const BezTriple segment_last_key = fcu->bezt[segment->start_index + segment->length - 1];
+    y_delta = right_key->vec[1][1] - segment_last_key.vec[1][1];
+  }
+  else {
+    const BezTriple segment_first_key = fcu->bezt[segment->start_index];
+    y_delta = left_key->vec[1][1] - segment_first_key.vec[1][1];
+  }
+
+  const float offset_value = y_delta * fabs(factor);
+  for (int i = segment->start_index; i < segment->start_index + segment->length; i++) {
+    const float key_y_value = fcu->bezt[i].vec[1][1] + offset_value;
+    BKE_fcurve_keyframe_move_value_with_handles(&fcu->bezt[i], key_y_value);
+  }
+}
+
+/* ---------------- */
+
 void breakdown_fcurve_segment(FCurve *fcu, FCurveSegment *segment, const float factor)
 {
   const BezTriple *left_bezt = fcurve_segment_start_get(fcu, segment->start_index);

source/blender/editors/include/ED_keyframes_edit.hh

@@ -458,6 +458,14 @@ void smooth_fcurve_segment(FCurve *fcu,
                            int kernel_size,
                            double *kernel);
 void ease_fcurve_segment(FCurve *fcu, FCurveSegment *segment, float factor);
+/**
+ * Shift the FCurve segment up/down so that it aligns with the key before/after
+ * the segment.
+ *
+ * \param factor blend factor from -1.0 to 1.0. The sign determines whether the
+ * segment is aligned with the key before or after the segment.
+ */
+void blend_offset_fcurve_segment(FCurve *fcu, FCurveSegment *segment, float factor);
 bool decimate_fcurve(bAnimListElem *ale, float remove_ratio, float error_sq_max);
 
 /**

source/blender/editors/space_graph/graph_intern.h

@@ -119,6 +119,7 @@ void GRAPH_OT_clean(struct wmOperatorType *ot);
 void GRAPH_OT_blend_to_neighbor(struct wmOperatorType *ot);
 void GRAPH_OT_breakdown(struct wmOperatorType *ot);
 void GRAPH_OT_ease(struct wmOperatorType *ot);
+void GRAPH_OT_blend_offset(struct wmOperatorType *ot);
 void GRAPH_OT_decimate(struct wmOperatorType *ot);
 void GRAPH_OT_blend_to_default(struct wmOperatorType *ot);
 void GRAPH_OT_butterworth_smooth(struct wmOperatorType *ot);

source/blender/editors/space_graph/graph_ops.cc

@@ -469,6 +469,7 @@ void graphedit_operatortypes()
   WM_operatortype_append(GRAPH_OT_blend_to_neighbor);
   WM_operatortype_append(GRAPH_OT_breakdown);
   WM_operatortype_append(GRAPH_OT_ease);
+  WM_operatortype_append(GRAPH_OT_blend_offset);
   WM_operatortype_append(GRAPH_OT_blend_to_default);
   WM_operatortype_append(GRAPH_OT_gaussian_smooth);
   WM_operatortype_append(GRAPH_OT_butterworth_smooth);

source/blender/editors/space_graph/graph_slider_ops.cc

@@ -983,6 +983,97 @@ void GRAPH_OT_ease(wmOperatorType *ot)
                        1.0f);
 }
 
+/* -------------------------------------------------------------------- */
+/** \name Blend Offset Operator
+ * \{ */
+
+static void blend_offset_graph_keys(bAnimContext *ac, const float factor)
+{
+  apply_fcu_segment_function(ac, factor, blend_offset_fcurve_segment);
+}
+
+static void blend_offset_draw_status_header(bContext *C, tGraphSliderOp *gso)
+{
+  common_draw_status_header(C, gso, "Blend Offset Keys");
+}
+
+static void blend_offset_modal_update(bContext *C, wmOperator *op)
+{
+  tGraphSliderOp *gso = static_cast<tGraphSliderOp *>(op->customdata);
+
+  blend_offset_draw_status_header(C, gso);
+
+  /* Reset keyframes to the state at invoke. */
+  reset_bezts(gso);
+  const float factor = slider_factor_get_and_remember(op);
+  blend_offset_graph_keys(&gso->ac, factor);
+  WM_event_add_notifier(C, NC_ANIMATION | ND_KEYFRAME | NA_EDITED, NULL);
+}
+
+static int blend_offset_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+  const int invoke_result = graph_slider_invoke(C, op, event);
+
+  if (invoke_result == OPERATOR_CANCELLED) {
+    return invoke_result;
+  }
+
+  tGraphSliderOp *gso = static_cast<tGraphSliderOp *>(op->customdata);
+  gso->modal_update = blend_offset_modal_update;
+  gso->factor_prop = RNA_struct_find_property(op->ptr, "factor");
+  blend_offset_draw_status_header(C, gso);
+  ED_slider_factor_bounds_set(gso->slider, -1, 1);
+  ED_slider_factor_set(gso->slider, 0.0f);
+
+  return invoke_result;
+}
+
+static int blend_offset_exec(bContext *C, wmOperator *op)
+{
+  bAnimContext ac;
+
+  /* Get editor data. */
+  if (ANIM_animdata_get_context(C, &ac) == 0) {
+    return OPERATOR_CANCELLED;
+  }
+
+  const float factor = RNA_float_get(op->ptr, "factor");
+
+  blend_offset_graph_keys(&ac, factor);
+
+  /* Set notifier that keyframes have changed. */
+  WM_event_add_notifier(C, NC_ANIMATION | ND_KEYFRAME | NA_EDITED, NULL);
+
+  return OPERATOR_FINISHED;
+}
+
+void GRAPH_OT_blend_offset(wmOperatorType *ot)
+{
+  /* Identifiers. */
+  ot->name = "Blend Offset Keyframes";
+  ot->idname = "GRAPH_OT_blend_offset";
+  ot->description = "Shift selected keys to the value of the neighboring keys as a block";
+
+  /* API callbacks. */
+  ot->invoke = blend_offset_invoke;
+  ot->modal = graph_slider_modal;
+  ot->exec = blend_offset_exec;
+  ot->poll = graphop_editable_keyframes_poll;
+
+  /* Flags. */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
+
+  RNA_def_float_factor(ot->srna,
+                       "factor",
+                       0.0f,
+                       -FLT_MAX,
+                       FLT_MAX,
+                       "Curve Bend",
+                       "Control the bend of the curve",
+                       -1.0f,
+                       1.0f);
+}
+
 /** \} */
 /* -------------------------------------------------------------------- */
 /** \name Gauss Smooth Operator