Implement a new automatic handle algorithm to produce smooth F-Curves.

The legacy algorithm only considers two adjacent points when computing
the bezier handles, which cannot produce satisfactory results. Animators
are often forced to manually adjust all curves.

The new approach instead solves a system of equations to trace a cubic spline
with continuous second derivative through the whole segment of auto points,
delimited at ends by keyframes with handles set by other requirements.

This algorithm also adjusts Vector handles that face ordinary bezier keyframes
to achieve zero acceleration at the Vector keyframe, instead of simply pointing
it at the adjacent point.

Original idea and implementation by Benoit Bolsee <benoit.bolsee@online.be>;
code mostly rewritten to improve code clarity and extensibility.

Reviewers: aligorith

Differential Revision: https://developer.blender.org/D2884

1 files changed, 10 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_fcurve.c b/source/blender/makesrna/intern/rna_fcurve.c
index b23b229a27d..c8ee6e15689 100644
--- a/source/blender/makesrna/intern/rna_fcurve.c
+++ b/source/blender/makesrna/intern/rna_fcurve.c
@@ -1895,6 +1895,11 @@ static void rna_def_fcurve(BlenderRNA *brna)
 		                      "Use custom hand-picked color for F-Curve"},
 		{0, NULL, 0, NULL, NULL}
 	};
+	static EnumPropertyItem prop_mode_smoothing_items[] = {
+		{FCURVE_SMOOTH_NONE, "NONE", 0, "None", "Auto handles only take adjacent keys into account (legacy mode)"},
+		{FCURVE_SMOOTH_CONT_ACCEL, "CONT_ACCEL", 0, "Continuous Acceleration", "Auto handles are placed to avoid jumps in acceleration"},
+		{0, NULL, 0, NULL, NULL}
+	};
 
 	srna = RNA_def_struct(brna, "FCurve", NULL);
 	RNA_def_struct_ui_text(srna, "F-Curve", "F-Curve defining values of a period of time");
@@ -1968,6 +1973,11 @@ static void rna_def_fcurve(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Hide", "F-Curve and its keyframes are hidden in the Graph Editor graphs");
 	RNA_def_property_update(prop, NC_SPACE | ND_SPACE_GRAPH, NULL);
 
+	prop = RNA_def_property(srna, "auto_smoothing", PROP_ENUM, PROP_NONE);
+	RNA_def_property_enum_items(prop, prop_mode_smoothing_items);
+	RNA_def_property_ui_text(prop, "Auto Handle Smoothing", "Algorithm used to compute automatic handles");
+	RNA_def_property_update(prop, NC_ANIMATION | ND_KEYFRAME | NA_EDITED, "rna_FCurve_update_data");
+
 	/* State Info (for Debugging) */
 	prop = RNA_def_property(srna, "is_valid", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_negative_sdna(prop, NULL, "flag", FCURVE_DISABLED);