Driver Keyframing: Some tweaks to make inserting keyframes on Driver F-Curves easier

Now, when trying to insert a keyframe on a driven property (using IKEY, or with
autokeying enabled), the keyframes will get created on the Driver's F-Curve
(instead of creating a new FCurve that goes into the active action, but will never
do anything). Furthermore, the x-value of the new keyframe will be the current
result of the driver expression.

Why/Motivations:
This way, it becomes easier to create corrective drivers, as you can position all
the targets the driver depends on, then adjust the driver value until it does what
you need, and then you keyframe that value to bake it into the Driver F-Curve
(in effect, "training" the computer how to behave in that case).

Usage Notes:
* In practice, that particular workflow is still quite clunky to achieve, due to some
  quirks of how the driver system and the UI widgets interact. Specifically, you'll
  need to disable/mute the driver before trying to edit the setting (to prevent the
  driver from immediately resetting the value - before even autokey fires!). However,
  if you're using the Graph Editor to preview/monitor/manage the keying process, you'll
  then want to re-enable the driver before changing the targets, so that you can see
  how much of a change you'll want to be applying!

* The warning about editing driver values may need to be disabled or selectively
  knocked out. I had it disabled while testing this functionality, but it's actually
  harmless in its current state (if just a bit annoying).

7 files changed, 50 insertions, 6 deletions

diff --git a/source/blender/blenkernel/BKE_fcurve.h b/source/blender/blenkernel/BKE_fcurve.h
index a1176b91312..ff2880ab311 100644
--- a/source/blender/blenkernel/BKE_fcurve.h
+++ b/source/blender/blenkernel/BKE_fcurve.h
@@ -99,6 +99,7 @@ void driver_variable_name_validate(struct DriverVar *dvar);
 struct DriverVar *driver_add_new_variable(struct ChannelDriver *driver);
 
 float driver_get_variable_value(struct ChannelDriver *driver, struct DriverVar *dvar);
+float evaluate_driver(struct ChannelDriver *driver, const float evaltime);
 
 /* ************** F-Curve Modifiers *************** */
 
diff --git a/source/blender/blenkernel/intern/fcurve.c b/source/blender/blenkernel/intern/fcurve.c
index 70fdcd12cf7..891ab7999fe 100644
--- a/source/blender/blenkernel/intern/fcurve.c
+++ b/source/blender/blenkernel/intern/fcurve.c
@@ -1777,7 +1777,7 @@ float driver_get_variable_value(ChannelDriver *driver, DriverVar *dvar)
  *	- "evaltime" is the frame at which F-Curve is being evaluated
  *  - has to return a float value
  */
-static float evaluate_driver(ChannelDriver *driver, const float evaltime)
+float evaluate_driver(ChannelDriver *driver, const float evaltime)
 {
 	DriverVar *dvar;
 	
diff --git a/source/blender/editors/animation/keyframing.c b/source/blender/editors/animation/keyframing.c
index 8841a05bcd8..0b0a24a24ef 100644
--- a/source/blender/editors/animation/keyframing.c
+++ b/source/blender/editors/animation/keyframing.c
@@ -930,6 +930,12 @@ bool insert_keyframe_direct(ReportList *reports, PointerRNA ptr, PropertyRNA *pr
 	/* update F-Curve flags to ensure proper behaviour for property type */
 	update_autoflags_fcurve_direct(fcu, prop);
 	
+	/* adjust frame on which to add keyframe */
+	if ((flag & INSERTKEY_DRIVER) && (fcu->driver)) {
+		/* for making it easier to add corrective drivers... */
+		cfra = evaluate_driver(fcu->driver, cfra);
+	}
+	
 	/* obtain value to give keyframe */
 	if ( (flag & INSERTKEY_MATRIX) && 
 	     (visualkey_can_use(&ptr, prop)) )
@@ -1743,6 +1749,7 @@ static int insert_key_button_exec(bContext *C, wmOperator *op)
 	PointerRNA ptr = {{NULL}};
 	PropertyRNA *prop = NULL;
 	char *path;
+	uiBut *but;
 	float cfra = (float)CFRA;
 	short success = 0;
 	int index;
@@ -1753,6 +1760,7 @@ static int insert_key_button_exec(bContext *C, wmOperator *op)
 	flag = ANIM_get_keyframing_flags(scene, 1);
 	
 	/* try to insert keyframe using property retrieved from UI */
+	but = UI_context_active_but_get(C);
 	UI_context_active_but_prop_get(C, &ptr, &prop, &index);
 	
 	if ((ptr.id.data && ptr.data && prop) && RNA_property_animateable(&ptr, prop)) {
@@ -1766,6 +1774,17 @@ static int insert_key_button_exec(bContext *C, wmOperator *op)
 			
 			success = insert_keyframe_direct(op->reports, ptr, prop, fcu, cfra, ts->keyframe_type, 0);
 		}
+		else if (UI_but_flag_is_set(but, UI_BUT_DRIVEN)) {
+			/* Driven property - Find driver */
+			FCurve *fcu;
+			int driven, special;
+			
+			fcu = rna_get_fcurve_context_ui(C, &ptr, prop, index, NULL, NULL, &driven, &special);
+			
+			if (fcu && driven) {
+				success = insert_keyframe_direct(op->reports, ptr, prop, fcu, cfra, ts->keyframe_type, INSERTKEY_DRIVER);
+			}
+		}
 		else {
 			/* standard properties */
 			path = RNA_path_from_ID_to_property(&ptr, prop);
diff --git a/source/blender/editors/include/UI_interface.h b/source/blender/editors/include/UI_interface.h
index a2408812643..9aad340d2fb 100644
--- a/source/blender/editors/include/UI_interface.h
+++ b/source/blender/editors/include/UI_interface.h
@@ -495,6 +495,7 @@ bool    UI_but_active_drop_color(struct bContext *C);
 
 void    UI_but_flag_enable(uiBut *but, int flag);
 void    UI_but_flag_disable(uiBut *but, int flag);
+bool    UI_but_flag_is_set(uiBut *but, int flag);
 
 void    UI_but_drawflag_enable(uiBut *but, int flag);
 void    UI_but_drawflag_disable(uiBut *but, int flag);
diff --git a/source/blender/editors/interface/interface.c b/source/blender/editors/interface/interface.c
index daef84c311f..fac1267cc62 100644
--- a/source/blender/editors/interface/interface.c
+++ b/source/blender/editors/interface/interface.c
@@ -3984,6 +3984,11 @@ void UI_but_flag_disable(uiBut *but, int flag)
 	but->flag &= ~flag;
 }
 
+bool UI_but_flag_is_set(uiBut *but, int flag)
+{
+	return (but->flag & flag) != 0;
+}
+
 void UI_but_drawflag_enable(uiBut *but, int flag)
 {
 	but->drawflag |= flag;
diff --git a/source/blender/editors/interface/interface_anim.c b/source/blender/editors/interface/interface_anim.c
index 178fda043b6..46967742652 100644
--- a/source/blender/editors/interface/interface_anim.c
+++ b/source/blender/editors/interface/interface_anim.c
@@ -242,24 +242,41 @@ void ui_but_anim_autokey(bContext *C, uiBut *but, Scene *scene, float cfra)
 			WM_event_add_notifier(C, NC_ANIMATION | ND_KEYFRAME | NA_EDITED, NULL);
 		}
 	}
-	else if (!driven) {
+	else if (driven) {
+		/* Driver - Try to insert keyframe using the driver's input as the frame,
+		 * making it easier to set up corrective drivers
+		 */
+		if (IS_AUTOKEY_ON(scene)) {
+			ReportList *reports = CTX_wm_reports(C);
+			ToolSettings *ts = scene->toolsettings;
+			PointerRNA ptr = {{NULL}};
+			PropertyRNA *prop = NULL;
+			int index;
+			
+			UI_context_active_but_prop_get(C, &ptr, &prop, &index);
+			
+			insert_keyframe_direct(reports, ptr, prop, fcu, cfra, ts->keyframe_type, INSERTKEY_DRIVER);
+			WM_event_add_notifier(C, NC_ANIMATION | ND_KEYFRAME | NA_EDITED, NULL);
+		}
+	}
+	else  {
 		id = but->rnapoin.id.data;
-
+		
 		/* TODO: this should probably respect the keyingset only option for anim */
 		if (autokeyframe_cfra_can_key(scene, id)) {
 			ReportList *reports = CTX_wm_reports(C);
 			ToolSettings *ts = scene->toolsettings;
 			short flag = ANIM_get_keyframing_flags(scene, 1);
-
+			
 			fcu->flag &= ~FCURVE_SELECTED;
-
+			
 			/* Note: We use but->rnaindex instead of fcu->array_index,
 			 *       because a button may control all items of an array at once.
 			 *       E.g., color wheels (see T42567). */
 			BLI_assert((fcu->array_index == but->rnaindex) || (but->rnaindex == -1));
 			insert_keyframe(reports, id, action, ((fcu->grp) ? (fcu->grp->name) : (NULL)),
 			                fcu->rna_path, but->rnaindex, cfra, ts->keyframe_type, flag);
-
+			
 			WM_event_add_notifier(C, NC_ANIMATION | ND_KEYFRAME | NA_EDITED, NULL);
 		}
 	}
diff --git a/source/blender/makesdna/DNA_anim_types.h b/source/blender/makesdna/DNA_anim_types.h
index fc32bbd1e99..c8ba61db87e 100644
--- a/source/blender/makesdna/DNA_anim_types.h
+++ b/source/blender/makesdna/DNA_anim_types.h
@@ -834,6 +834,7 @@ typedef enum eInsertKeyFlags {
 	/* Allow to make a full copy of new key into existing one, if any, instead of 'reusing' existing handles.
 	 * Used by copy/paste code. */
 	INSERTKEY_OVERWRITE_FULL = (1<<7),
+	INSERTKEY_DRIVER    = (1<<8),	/* for driver FCurves, use driver's "input" value - for easier corrective driver setup */
 } eInsertKeyFlags;
 
 /* ************************************************ */