Driver Setup Workflow Improvement: Property Eyedropper

This commit brings some long requested improvements to the workflow for setting up
drivers, which should make it easier and faster to set up new drivers in a more
interactive fashion.

The new workflow is as follows:
1) Hover over the property (e.g. "Lamp Energy" or "Y Location") or properties ("Rotation")
   you wish to add drivers to. We'll refer to this as the "destination"
2) Ctrl-D to active the new "Add Drivers" eyedropper
3) Click on the property you want to use as the source/target. The property under the
   mouse will be used to drive the property you invoked Ctrl-D on.

For example, to drive the X, Y, and Z location of the Cube using the Y Location of the Lamp,
hover over any of the X/Y/Z location buttons, hit Ctrl-D, then click on the Y-Location
button of the Lamp object. Drivers will be added to the X, Y, and Z Location properties
of the Cube; each driver will have a single variable, which uses the Y-Location Transform
Channel of the Lamp.


Tips:
- Transform properties will automatically create "Transform Channel" driver variables.
  Everything else will use "Single Property" ones

- Due to the way that Blender's UI Context works, you'll need two Properties Panel instances
  open (and to have pinned one of the two to show the properties for the unselected
  object). It's slightly clunky, but necessary for implementing a workflow like this,
  as the UI cannot be manipulated while using eyedroppers to pick data.

- The eyedropper operator implemented here actually has three modes of operation.
  1) The "1-N" (one to many) mode is the default used for Ctrl-D, and "Add Driver to All"
     in the RMB Menu. This is the behaviour described above.
  2) There's also a "1-1" (one to one) mode that is used for the "Add Single Driver" in the
     RMB Menu.
  3) Finally, there's the "N-N" mode (many to many), which isn't currently exposed.
     The point of this is to allow mapping XYZ to XYZ elementwise (i.e. direct copying)
     which is useful for things like locations, rotations, scaling, and colours.


Implementation Notes:
- The bulk of the driver adding logic is in editors/animation/drivers.c, where most of
  the Driver UI operators and tools are defined

- The property eyedropper code is in interface_eyedropper.c along with all the other
  eyedroppers (even though they don't share much actual code in common). However, this
  turns out to be necessary, as we can't get access to many of the low-level buttons API's
  otherwise.

Todo:
- It may be necessary to restore a way to access the old behaviour (i.e. "manual setup")
  in case it is not practical to immediately pick a property.

- Other things to investigate here include extra hotkeys (e.g. Ctrl-Shift-D for Add Single?),
  and to expose the N-N mode.

- Other things we could try include interactively applying scaling factors, picking
  multiple targets (e.g. for location difference and rotation difference drivers),
  and/or other ways of using these property picking methods.

1 files changed, 208 insertions, 19 deletions

diff --git a/source/blender/editors/animation/drivers.c b/source/blender/editors/animation/drivers.c
index 1f77ddc73b1..65a235e88f6 100644
--- a/source/blender/editors/animation/drivers.c
+++ b/source/blender/editors/animation/drivers.c
@@ -37,6 +37,7 @@
 
 #include "BLI_blenlib.h"
 #include "BLI_utildefines.h"
+#include "BLI_string.h"
 
 #include "DNA_anim_types.h"
 #include "DNA_texture_types.h"
@@ -154,6 +155,198 @@ FCurve *verify_driver_fcurve(ID *id, const char rna_path[], const int array_inde
 /* ************************************************** */
 /* Driver Management API */
 
+/* Mapping Types enum for operators */
+// XXX: These names need reviewing
+EnumPropertyItem prop_driver_create_mapping_types[] = {
+	{CREATEDRIVER_MAPPING_1_N, "SINGLE_MANY", 0, "Single Target, Multiple Properties",
+	 "Use the picked item to drive all components of this property"},
+	{CREATEDRIVER_MAPPING_1_1, "DIRECT", 0, "Single Item Only",
+	 "Use picked item to drive property under mouse"},
+	{CREATEDRIVER_MAPPING_N_N, "MATCH", 0, "Match Indices",
+	 "Create drivers for each pair of corresponding elements"},
+	{0, NULL, 0, NULL, NULL}
+};
+
+/* --------------------------------- */
+
+/* Helper for ANIM_add_driver_with_target - Adds the actual driver */
+static int add_driver_with_target(
+        ReportList *reports,
+        ID *dst_id, const char dst_path[], int dst_index,
+        ID *src_id, const char src_path[], int src_index,
+        PointerRNA *src_ptr, PropertyRNA *src_prop,
+        short flag, int driver_type)
+{
+	FCurve *fcu;
+	short add_mode = (flag & CREATEDRIVER_WITH_FMODIFIER) ? 2 : 1;
+	const char *prop_name = RNA_property_identifier(src_prop);
+	
+	/* Create F-Curve with Driver */
+	fcu = verify_driver_fcurve(dst_id, dst_path, dst_index, add_mode);
+	
+	if (fcu && fcu->driver) {
+		ChannelDriver *driver = fcu->driver;
+		DriverVar *dvar;
+		
+		/* Set the type of the driver */
+		driver->type = driver_type;
+		BLI_strncpy(driver->expression, "var", sizeof(driver->expression)); /* XXX: if we have N-1 mapping, we need to include all those here... */
+		
+		/* Create a driver variable for the target
+		 *   - For transform properties, we want to automatically use "transform channel" instead
+		 *     (The only issue is with quat rotations vs euler channels...)
+		 */
+		dvar = driver_add_new_variable(driver);
+		
+		if (ELEM(src_ptr->type, &RNA_Object, &RNA_PoseBone) &&  
+			(STREQ(prop_name, "location") || STREQ(prop_name, "scale") || strstr(prop_name, "rotation_"))) 
+		{
+			/* Transform Channel */
+			DriverTarget *dtar;
+			
+			driver_change_variable_type(dvar, DVAR_TYPE_TRANSFORM_CHAN);
+			dtar = &dvar->targets[0];
+			
+			/* Bone or Object target? */
+			dtar->id = src_id;
+			dtar->idtype = GS(src_id->name);
+			
+			if (src_ptr->type == &RNA_PoseBone) {
+				RNA_string_get(src_ptr, "name", dtar->pchan_name);
+			}
+			
+			/* Transform channel depends on type */
+			if (STREQ(prop_name, "location")) {
+				if (src_index == 2)
+					dtar->transChan = DTAR_TRANSCHAN_LOCZ;
+				else if (src_index == 1)
+					dtar->transChan = DTAR_TRANSCHAN_LOCY;
+				else
+					dtar->transChan = DTAR_TRANSCHAN_LOCX;
+			}
+			else if (STREQ(prop_name, "scale")) {
+				if (src_index == 2)
+					dtar->transChan = DTAR_TRANSCHAN_SCALEZ;
+				else if (src_index == 1)
+					dtar->transChan = DTAR_TRANSCHAN_SCALEY;
+				else
+					dtar->transChan = DTAR_TRANSCHAN_SCALEX;
+			}
+			else {
+				/* XXX: With quaternions and axis-angle, this mapping might not be correct...
+				 *      But since those have 4 elements instead, there's not much we can do
+				 */
+				if (src_index == 2)
+					dtar->transChan = DTAR_TRANSCHAN_ROTZ;
+				else if (src_index == 1)
+					dtar->transChan = DTAR_TRANSCHAN_ROTY;
+				else
+					dtar->transChan = DTAR_TRANSCHAN_ROTX;
+			}
+		}
+		else {
+			/* Single RNA Property */
+			DriverTarget *dtar = &dvar->targets[0];
+			
+			/* ID is as-is */
+			dtar->id = src_id;
+			dtar->idtype = GS(src_id->name);
+			
+			/* Need to make a copy of the path (or build one with array index built in) */
+			if (RNA_property_array_check(src_prop)) {
+				dtar->rna_path = BLI_sprintfN("%s[%d]", src_path, src_index);
+			}
+			else {
+				dtar->rna_path = BLI_strdup(src_path);
+			}
+		}
+	}
+	
+	/* set the done status */
+	return (fcu != NULL);
+}
+
+/* Main Driver Management API calls:
+ *  Add a new driver for the specified property on the given ID block,
+ *  and make it be driven by the specified target.
+ *
+ * This is intended to be used in conjunction with a modal "eyedropper"
+ * for picking the variable that is going to be used to drive this one.
+ *
+ * - flag: eCreateDriverFlags
+ * - driver_type: eDriver_Types
+ * - mapping_type: eCreateDriver_MappingTypes
+ */
+int ANIM_add_driver_with_target(
+        ReportList *reports, 
+        ID *dst_id, const char dst_path[], int dst_index,
+        ID *src_id, const char src_path[], int src_index,
+        short flag, int driver_type, short mapping_type)
+{
+	PointerRNA id_ptr, ptr;
+	PropertyRNA *prop;
+	
+	PointerRNA id_ptr2, ptr2;
+	PropertyRNA *prop2;
+	int done_tot = 0;
+	
+	/* validate pointers first - exit if failure */
+	RNA_id_pointer_create(dst_id, &id_ptr);
+	if (RNA_path_resolve_property(&id_ptr, dst_path, &ptr, &prop) == false) {
+		BKE_reportf(reports, RPT_ERROR, 
+		            "Could not add driver, as RNA path is invalid for the given ID (ID = %s, path = %s)",
+		            dst_id->name, dst_path);
+		return 0;
+	}
+	
+	RNA_id_pointer_create(src_id, &id_ptr2);
+	if (RNA_path_resolve_property(&id_ptr2, src_path, &ptr2, &prop2) == false) {
+		/* No target - So, fall back to default method for adding a "simple" driver normally */
+		return ANIM_add_driver(reports, dst_id, dst_path, dst_index, flag, driver_type);
+	}
+	
+	/* handle curve-property mappings based on mapping_type */
+	switch (mapping_type) {
+		case CREATEDRIVER_MAPPING_N_N: /* N-N - Try to match as much as possible, then use the first one */
+		{
+			/* Use the shorter of the two (to avoid out of bounds access) */
+			int dst_len = (RNA_property_array_check(prop)) ? RNA_property_array_length(&ptr, prop) : 1;
+			int src_len = (RNA_property_array_check(prop)) ? RNA_property_array_length(&ptr2, prop2) : 1;
+			
+			int len = MIN2(dst_len, src_len);
+			int i;
+			
+			for (i = 0; i < len; i++) {
+				done_tot += add_driver_with_target(reports, dst_id, dst_path, i, src_id, src_path, i, &ptr2, prop2, flag, driver_type);
+			}
+			break;
+		}
+		
+		case CREATEDRIVER_MAPPING_1_N: /* 1-N - Specified target index for all */
+		default:
+		{
+			int len = (RNA_property_array_check(prop)) ? RNA_property_array_length(&ptr, prop) : 1;
+			int i;
+			
+			for (i = 0; i < len; i++) {
+				done_tot += add_driver_with_target(reports, dst_id, dst_path, i, src_id, src_path, src_index, &ptr2, prop2, flag, driver_type);
+			}
+			break;
+		}
+		
+		case CREATEDRIVER_MAPPING_1_1: /* 1-1 - Use the specified index (unless -1) */
+		{
+			done_tot = add_driver_with_target(reports, dst_id, dst_path, dst_index, src_id, src_path, src_index, &ptr2, prop2, flag, driver_type);
+			break;
+		}
+	}
+	
+	/* done */
+	return done_tot;
+}
+
+/* --------------------------------- */
+
 /* Main Driver Management API calls:
  *  Add a new driver for the specified property on the given ID block
  */
@@ -427,35 +620,31 @@ static int add_driver_button_exec(bContext *C, wmOperator *op)
 {
 	PointerRNA ptr = {{NULL}};
 	PropertyRNA *prop = NULL;
-	int success = 0;
 	int index;
+	
 	const bool all = RNA_boolean_get(op->ptr, "all");
+	int ret = OPERATOR_CANCELLED;
 	
 	/* try to create driver using property retrieved from UI */
 	UI_context_active_but_prop_get(C, &ptr, &prop, &index);
 	
-	if (all)
-		index = -1;
-	
 	if (ptr.id.data && ptr.data && prop && RNA_property_animateable(&ptr, prop)) {
-		char *path = BKE_animdata_driver_path_hack(C, &ptr, prop, NULL);
-		short flags = CREATEDRIVER_WITH_DEFAULT_DVAR;
+		wmOperatorType *ot = WM_operatortype_find("UI_OT_eyedropper_driver", true);
+		PointerRNA op_ptr;
 		
-		if (path) {
-			success += ANIM_add_driver(op->reports, ptr.id.data, path, index, flags, DRIVER_TYPE_PYTHON);
-			
-			MEM_freeN(path);
-		}
-	}
-	
-	if (success) {
-		/* send updates */
-		UI_context_update_anim_flag(C);
-		DAG_relations_tag_update(CTX_data_main(C));
-		WM_event_add_notifier(C, NC_ANIMATION | ND_FCURVES_ORDER, NULL); // XXX
+		WM_operator_properties_create_ptr(&op_ptr, ot);
+		
+		if (all)
+			RNA_enum_set(&op_ptr, "mapping_type", CREATEDRIVER_MAPPING_1_N);
+		else
+			RNA_enum_set(&op_ptr, "mapping_type", CREATEDRIVER_MAPPING_1_1);
+		
+		ret = WM_operator_name_call_ptr(C, ot, WM_OP_INVOKE_DEFAULT, &op_ptr);
+		
+		WM_operator_properties_free(&op_ptr);
 	}
 	
-	return (success) ? OPERATOR_FINISHED : OPERATOR_CANCELLED;
+	return ret;
 }
 
 void ANIM_OT_driver_button_add(wmOperatorType *ot)