Animation: Scale Average slider for Graph Editor

This patch has been originally authored by Ares Deveaux #106526

Scale the selected key segments to their average
Unlike just scaling using the transform tools, this scales to the average of each individual F-Curve segment.

Co-authored-by: Ares Deveaux <aresdevo@gmail.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/111744

scripts/startup/bl_ui/space_graph.py

@@ -325,6 +325,7 @@ class GRAPH_MT_key_blending(Menu):
         layout.operator("graph.blend_to_ease", text="Blend to Ease")
         layout.operator("graph.match_slope", text="Match Slope")
         layout.operator("graph.shear", text="Shear Keys")
+        layout.operator("graph.scale_average", text="Scale Average")
 
 
 class GRAPH_MT_key_smoothing(Menu):

source/blender/editors/animation/keyframes_general.cc

@@ -390,6 +390,25 @@ void blend_to_default_fcurve(PointerRNA *id_ptr, FCurve *fcu, const float factor
 
 /* ---------------- */
 
+void scale_average_fcurve_segment(FCurve *fcu, FCurveSegment *segment, const float factor)
+{
+  float y = 0;
+
+  /* Find first the average of the y values to then use it in the final calculation. */
+  for (int i = segment->start_index; i < segment->start_index + segment->length; i++) {
+    y += fcu->bezt[i].vec[1][1];
+  }
+
+  const float y_average = y / segment->length;
+
+  for (int i = segment->start_index; i < segment->start_index + segment->length; i++) {
+    const float key_y_value = interpf(y_average, fcu->bezt[i].vec[1][1], 1 - factor);
+    BKE_fcurve_keyframe_move_value_with_handles(&fcu->bezt[i], key_y_value);
+  }
+}
+
+/* ---------------- */
+
 struct ButterworthCoefficients {
   double *A, *d1, *d2;
   int filter_order;

source/blender/editors/include/ED_keyframes_edit.hh

@@ -430,6 +430,7 @@ ListBase find_fcurve_segments(FCurve *fcu);
 void clean_fcurve(bAnimContext *ac, bAnimListElem *ale, float thresh, bool cleardefault);
 void blend_to_neighbor_fcurve_segment(FCurve *fcu, FCurveSegment *segment, float factor);
 void breakdown_fcurve_segment(FCurve *fcu, FCurveSegment *segment, float factor);
+void scale_average_fcurve_segment(struct FCurve *fcu, struct FCurveSegment *segment, float factor);
 
 /**
  * Get a 1D gauss kernel. Since the kernel is symmetrical, only calculates the positive side.

source/blender/editors/space_graph/graph_intern.h

@@ -123,6 +123,7 @@ 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_shear(struct wmOperatorType *ot);
+void GRAPH_OT_scale_average(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

@@ -470,6 +470,7 @@ void graphedit_operatortypes()
   WM_operatortype_append(GRAPH_OT_breakdown);
   WM_operatortype_append(GRAPH_OT_ease);
   WM_operatortype_append(GRAPH_OT_shear);
+  WM_operatortype_append(GRAPH_OT_scale_average);
   WM_operatortype_append(GRAPH_OT_blend_offset);
   WM_operatortype_append(GRAPH_OT_blend_to_ease);
   WM_operatortype_append(GRAPH_OT_match_slope);

source/blender/editors/space_graph/graph_slider_ops.cc

@@ -1457,6 +1457,94 @@ void GRAPH_OT_shear(wmOperatorType *ot)
                "Which end of the segment to use as a reference to shear from");
 }
 
+/* -------------------------------------------------------------------- */
+/** \name Scale Average Operator
+ * \{ */
+
+static void scale_average_graph_keys(bAnimContext *ac, const float factor)
+{
+  apply_fcu_segment_function(ac, factor, scale_average_fcurve_segment);
+}
+
+static void scale_average_modal_update(bContext *C, wmOperator *op)
+{
+  tGraphSliderOp *gso = static_cast<tGraphSliderOp *>(op->customdata);
+
+  common_draw_status_header(C, gso, "Scale to Average");
+
+  /* Reset keyframes to the state at invoke. */
+  reset_bezts(gso);
+  const float factor = slider_factor_get_and_remember(op);
+  scale_average_graph_keys(&gso->ac, factor);
+  WM_event_add_notifier(C, NC_ANIMATION | ND_KEYFRAME | NA_EDITED, NULL);
+}
+
+static int scale_average_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 = scale_average_modal_update;
+  gso->factor_prop = RNA_struct_find_property(op->ptr, "factor");
+  common_draw_status_header(C, gso, "Scale to Average");
+  ED_slider_factor_bounds_set(gso->slider, 0, 2);
+  ED_slider_factor_set(gso->slider, 1.0f);
+
+  return invoke_result;
+}
+
+static int scale_average_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");
+
+  scale_average_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_scale_average(wmOperatorType *ot)
+{
+  /* Identifiers. */
+  ot->name = "Scale Average Keyframes";
+  ot->idname = "GRAPH_OT_scale_average";
+  ot->description =
+      "Increase or decrease the value of selected keys \n\
+  in relationship to their average";
+
+  /* API callbacks. */
+  ot->invoke = scale_average_invoke;
+  ot->modal = graph_slider_modal;
+  ot->exec = scale_average_exec;
+  ot->poll = graphop_editable_keyframes_poll;
+
+  /* Flags. */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_BLOCKING | OPTYPE_GRAB_CURSOR_X;
+
+  RNA_def_float_factor(ot->srna,
+                       "factor",
+                       1.0f,
+                       -FLT_MAX,
+                       FLT_MAX,
+                       "Scale Factor",
+                       "The scale factor applied to the curve segments",
+                       0.0f,
+                       2.0f);
+}
+
 /** \} */
 /* -------------------------------------------------------------------- */
 /** \name Gauss Smooth Operator