scripts/startup/bl_ui/space_graph.py

@@ -301,6 +301,7 @@ class GRAPH_MT_key_blending(Menu):
         layout.operator("graph.ease", text="Ease")
         layout.operator("graph.blend_offset", text="Blend Offset")
         layout.operator("graph.blend_to_ease", text="Blend to Ease")
+        layout.operator("graph.match_slope", text="Match Slope")
 
 
 class GRAPH_MT_key_smoothing(Menu):

source/blender/editors/animation/keyframes_general.cc

@@ -773,6 +773,58 @@ void blend_to_ease_fcurve_segment(FCurve *fcu, FCurveSegment *segment, const flo
 
 /* ---------------- */
 
+bool match_slope_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);
+
+  BezTriple beyond_key;
+  const BezTriple *reference_key;
+
+  if (factor >= 0) {
+    /* Stop the function if there is no key beyond the the right neighboring one. */
+    if (segment->start_index + segment->length >= fcu->totvert - 1) {
+      return false;
+    }
+    reference_key = right_key;
+    beyond_key = fcu->bezt[segment->start_index + segment->length + 1];
+  }
+  else {
+    /* Stop the function if there is no key beyond the left neighboring one. */
+    if (segment->start_index <= 1) {
+      return false;
+    }
+    reference_key = left_key;
+    beyond_key = fcu->bezt[segment->start_index - 2];
+  }
+
+  /* This delta values are used to get the relationship between the bookend keys and the
+   * reference keys beyong those. */
+  const float y_delta = beyond_key.vec[1][1] - reference_key->vec[1][1];
+  const float x_delta = beyond_key.vec[1][0] - reference_key->vec[1][0];
+
+  /* Avoids dividing by 0. */
+  if (x_delta == 0) {
+    return false;
+  }
+
+  for (int i = segment->start_index; i < segment->start_index + segment->length; i++) {
+
+    /* These new deltas are used to determine the relationship between the current key and the
+     * bookend ones. */
+    const float new_x_delta = fcu->bezt[i].vec[1][0] - reference_key->vec[1][0];
+    const float new_y_delta = new_x_delta * y_delta / x_delta;
+
+    const float delta = reference_key->vec[1][1] + new_y_delta - fcu->bezt[i].vec[1][1];
+
+    const float key_y_value = fcu->bezt[i].vec[1][1] + delta * fabs(factor);
+    BKE_fcurve_keyframe_move_value_with_handles(&fcu->bezt[i], key_y_value);
+  }
+  return true;
+}
+
+/* ---------------- */
+
 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

@@ -468,6 +468,7 @@ void ease_fcurve_segment(FCurve *fcu, FCurveSegment *segment, float factor);
 void blend_offset_fcurve_segment(FCurve *fcu, FCurveSegment *segment, float factor);
 void blend_to_ease_fcurve_segment(FCurve *fcu, FCurveSegment *segment, float factor);
 bool decimate_fcurve(bAnimListElem *ale, float remove_ratio, float error_sq_max);
+bool match_slope_fcurve_segment(FCurve *fcu, FCurveSegment *segment, float factor);
 
 /**
  * Blends the selected keyframes to the default value of the property the F-curve drives.

source/blender/editors/space_graph/graph_intern.h

@@ -121,6 +121,7 @@ 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_blend_to_ease(struct wmOperatorType *ot);
+void GRAPH_OT_match_slope(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

@@ -471,6 +471,7 @@ void graphedit_operatortypes()
   WM_operatortype_append(GRAPH_OT_ease);
   WM_operatortype_append(GRAPH_OT_blend_offset);
   WM_operatortype_append(GRAPH_OT_blend_to_ease);
+  WM_operatortype_append(GRAPH_OT_match_slope);
   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

@@ -1166,6 +1166,126 @@ void GRAPH_OT_blend_to_ease(wmOperatorType *ot)
                        1.0f);
 }
 
+/* -------------------------------------------------------------------- */
+/** \name Match Slope
+ * \{ */
+
+static void match_slope_graph_keys(bAnimContext *ac, const float factor)
+{
+  ListBase anim_data = {NULL, NULL};
+
+  bool all_segments_valid = true;
+
+  ANIM_animdata_filter(
+      ac, &anim_data, OPERATOR_DATA_FILTER, ac->data, eAnimCont_Types(ac->datatype));
+  LISTBASE_FOREACH (bAnimListElem *, ale, &anim_data) {
+    FCurve *fcu = (FCurve *)ale->key_data;
+    ListBase segments = find_fcurve_segments(fcu);
+
+    LISTBASE_FOREACH (FCurveSegment *, segment, &segments) {
+      all_segments_valid = match_slope_fcurve_segment(fcu, segment, factor);
+    }
+
+    ale->update |= ANIM_UPDATE_DEFAULT;
+    BLI_freelistN(&segments);
+  }
+
+  if(!all_segments_valid) {
+    if (factor >= 0){
+      WM_report(RPT_WARNING, "You need at least 2 keys to the right side of the selection.");
+    }
+    else {
+      WM_report(RPT_WARNING, "You need at least 2 keys to the left side of the selection.");
+    }
+  }
+  
+  ANIM_animdata_update(ac, &anim_data);
+  ANIM_animdata_freelist(&anim_data);
+}
+
+static void match_slope_draw_status_header(bContext *C, tGraphSliderOp *gso)
+{
+  common_draw_status_header(C, gso, "Match Slope");
+}
+
+static void match_slope_modal_update(bContext *C, wmOperator *op)
+{
+  tGraphSliderOp *gso = static_cast<tGraphSliderOp *>(op->customdata);
+
+  match_slope_draw_status_header(C, gso);
+
+  /* Reset keyframes to the state at invoke. */
+  reset_bezts(gso);
+  const float factor = slider_factor_get_and_remember(op);
+  match_slope_graph_keys(&gso->ac, factor);
+  WM_event_add_notifier(C, NC_ANIMATION | ND_KEYFRAME | NA_EDITED, NULL);
+}
+
+static int match_slope_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 = match_slope_modal_update;
+  gso->factor_prop = RNA_struct_find_property(op->ptr, "factor");
+  match_slope_draw_status_header(C, gso);
+  ED_slider_allow_overshoot_set(gso->slider, false, false);
+  ED_slider_factor_bounds_set(gso->slider, -1, 1);
+  ED_slider_factor_set(gso->slider, 0.0f);
+
+  return invoke_result;
+}
+
+static int match_slope_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");
+
+  match_slope_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_match_slope(wmOperatorType *ot)
+{
+  /* Identifiers. */
+  ot->name = "Match Slope";
+  ot->idname = "GRAPH_OT_match_slope";
+  ot->description = "Blend selected keys to the slope of neighboring ones";
+
+  /* API callbacks. */
+  ot->invoke = match_slope_invoke;
+  ot->modal = graph_slider_modal;
+  ot->exec = match_slope_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,
+                       "Factor",
+                       "Defines which keys to use as slope and how much to blend towards them",
+                       -1.0f,
+                       1.0f);
+}
+
 /** \} */
 /* -------------------------------------------------------------------- */
 /** \name Gauss Smooth Operator