GP Interpolate Sequence: Tool settings for controlling the shape of interpolation

This commit introduces the ability to use the Robert Penner easing equations
or a Custom Curve to control the way that the "Interpolate Sequence" operator
interpolates between keyframes. Previously, it was only possible to get linear
interpolation between the gp frames.

Workflow:
1) Place current frame between a pair of GP keyframes
2) Open the "Interpolate" panel in the Toolshelf
3) Choose the interpolation type (under "Sequence Options")
4) Adjust settings (e.g. if you're using "Custom Curve", use the curvemap widget
   to define the way that the interpolation proceeds)
5) Click "Sequence" to interpolate
6) Play back/scrub the animation to see if you've got the result you want
7) If you need to make some tweaks, undo, or delete the generated keyframes,
   then repeat the process again from step 4 until you've got the desired result.

1 files changed, 29 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 4d09457b3cc..8ee15ef21a3 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1218,6 +1218,14 @@ typedef enum eGP_BrushEdit_SettingsFlag {
 /* Settings for GP Interpolation Operators */
 typedef struct GP_Interpolate_Settings {
 	short flag;                        /* eGP_Interpolate_SettingsFlag */
+	
+	char type;                         /* eGP_Interpolate_Type - Interpolation Mode */ 
+	char easing;                       /* eBezTriple_Easing - Easing mode (if easing equation used) */
+	
+	float back;                        /* BEZT_IPO_BACK */
+	float amplitude, period;           /* BEZT_IPO_ELASTIC */
+	
+	struct CurveMapping *custom_ipo;   /* custom interpolation curve (for use with GP_IPO_CURVEMAP) */
 } GP_Interpolate_Settings;
 
 /* GP_Interpolate_Settings.flag */
@@ -1228,6 +1236,27 @@ typedef enum eGP_Interpolate_SettingsFlag {
 	GP_TOOLFLAG_INTERPOLATE_ONLY_SELECTED = (1 << 1),
 } eGP_Interpolate_SettingsFlag;
 
+/* GP_Interpolate_Settings.type */
+typedef enum eGP_Interpolate_Type {
+	/* Traditional Linear Interpolation */
+	GP_IPO_LINEAR   = 0,
+	
+	/* CurveMap Defined Interpolation */
+	GP_IPO_CURVEMAP = 1,
+	
+	/* Easing Equations */
+	GP_IPO_BACK = 3,
+	GP_IPO_BOUNCE = 4,
+	GP_IPO_CIRC = 5,
+	GP_IPO_CUBIC = 6,
+	GP_IPO_ELASTIC = 7,
+	GP_IPO_EXPO = 8,
+	GP_IPO_QUAD = 9,
+	GP_IPO_QUART = 10,
+	GP_IPO_QUINT = 11,
+	GP_IPO_SINE = 12,
+} eGP_Interpolate_Type;
+
 
 /* *************************************************************** */
 /* Transform Orientations */