Fix: allow curve of driver to be evaluated individually

This is necessary when adding a new keyframe to a fcurve
that also has a driver.

Reviewers: brecht, campbellbarton

Differential Revision: https://developer.blender.org/D4278

source/blender/blenkernel/BKE_fcurve.h

@@ -297,6 +297,7 @@ void correct_bezpart(float v1[2], float v2[2], float v3[2], float v4[2]);
 
 /* evaluate fcurve */
 float evaluate_fcurve(struct FCurve *fcu, float evaltime);
+float evaluate_fcurve_only_curve(struct FCurve *fcu, float evaltime);
 float evaluate_fcurve_driver(struct PathResolvedRNA *anim_rna, struct FCurve *fcu,
                              struct ChannelDriver *driver_orig, float evaltime);
 /* evaluate fcurve and store value */

source/blender/blenkernel/intern/fcurve.c

@@ -2799,6 +2799,14 @@ float evaluate_fcurve(FCurve *fcu, float evaltime)
 	return evaluate_fcurve_ex(fcu, evaltime, 0.0);
 }
 
+float evaluate_fcurve_only_curve(FCurve *fcu, float evaltime)
+{
+	/* Can be used to evaluate the (keyframed) fcurve only.
+	 * Also works for driver-fcurves when the driver itself is not relevant.
+	 * E.g. when inserting a keyframe in a driver fcurve. */
+	return evaluate_fcurve_ex(fcu, evaltime, 0.0);
+}
+
 float evaluate_fcurve_driver(PathResolvedRNA *anim_rna, FCurve *fcu, ChannelDriver *driver_orig, float evaltime)
 {
 	BLI_assert(fcu->driver != NULL);

source/blender/editors/space_graph/graph_edit.c

@@ -616,7 +616,7 @@ static void insert_graph_keys(bAnimContext *ac, eGraphKeys_InsertKey_Types mode)
 				else if (adt)
 					cfra = BKE_nla_tweakedit_remap(adt, (float)CFRA, NLATIME_CONVERT_UNMAP);
 
-				const float curval = evaluate_fcurve(fcu, cfra);
+				const float curval = evaluate_fcurve_only_curve(fcu, cfra);
 				insert_vert_fcurve(fcu, cfra, curval, ts->keyframe_type, 0);
 			}