Two in one:

- Bugfix #25937
  Child-of constraint now behaves like regular parent-child
  relationship when all options are set. This prevents the 
  errors that can happen when decomposing non-uniform matrices.

- Todo item
  The area corner hotspots for splitting/merging were far too
  narrow. Now it uses a circular distance to detect whether
  the hotspot is active. Also cleaned up drawing code for it.

source/blender/blenkernel/intern/constraint.c

@@ -834,7 +834,23 @@ static void childof_evaluate (bConstraint *con, bConstraintOb *cob, ListBase *ta
 	
 	/* only evaluate if there is a target */
 	if (VALID_CONS_TARGET(ct)) {
-		float parmat[4][4], invmat[4][4], tempmat[4][4];
+		float parmat[4][4];
+		
+		/* simple matrix parenting */
+		if(data->flag == CHILDOF_ALL) {
+			
+			/* multiply target (parent matrix) by offset (parent inverse) to get 
+			 * the effect of the parent that will be exherted on the owner
+			 */
+			mul_m4_m4m4(parmat, data->invmat, ct->matrix);
+			
+			/* now multiply the parent matrix by the owner matrix to get the 
+			 * the effect of this constraint (i.e.  owner is 'parented' to parent)
+			 */
+			mul_m4_m4m4(cob->matrix, cob->matrix, parmat);
+		}
+		else {
+			float invmat[4][4], tempmat[4][4];
 			float loc[3], eul[3], size[3];
 			float loco[3], eulo[3], sizo[3];
 			
@@ -883,6 +899,7 @@ static void childof_evaluate (bConstraint *con, bConstraintOb *cob, ListBase *ta
 			if (!(data->flag & CHILDOF_LOCY)) cob->matrix[3][1]= tempmat[3][1];
 			if (!(data->flag & CHILDOF_LOCZ)) cob->matrix[3][2]= tempmat[3][2];	
 		}
+	}
 }
 
 /* XXX note, con->flag should be CONSTRAINT_SPACEONCE for bone-childof, patched in readfile.c */

source/blender/editors/screen/area.c

@@ -164,27 +164,22 @@ void ED_area_overdraw_flush(ScrArea *sa, ARegion *ar)
 
 static void area_draw_azone(short x1, short y1, short x2, short y2)
 {
-	float xmin = x1;
+	int dx= floor(0.3f*(x2-x1));
-	float xmax = x2-2;
+	int dy= floor(0.3f*(y2-y1));
-	float ymin = y1-1;
-	float ymax = y2-3;
-	
-	float dx= 0.3f*(xmax-xmin);
-	float dy= 0.3f*(ymax-ymin);
 	
 	glColor4ub(255, 255, 255, 180);
-	fdrawline(xmin, ymax, xmax, ymin);
+	fdrawline(x1, y2, x2, y1);
 	glColor4ub(255, 255, 255, 130);
-	fdrawline(xmin, ymax-dy, xmax-dx, ymin);
+	fdrawline(x1, y2-dy, x2-dx, y1);
 	glColor4ub(255, 255, 255, 80);
-	fdrawline(xmin, ymax-2*dy, xmax-2*dx, ymin);
+	fdrawline(x1, y2-2*dy, x2-2*dx, y1);
 	
 	glColor4ub(0, 0, 0, 210);
-	fdrawline(xmin, ymax+1, xmax+1, ymin);
+	fdrawline(x1, y2+1, x2+1, y1);
 	glColor4ub(0, 0, 0, 180);
-	fdrawline(xmin, ymax-dy+1, xmax-dx+1, ymin);
+	fdrawline(x1, y2-dy+1, x2-dx+1, y1);
 	glColor4ub(0, 0, 0, 150);
-	fdrawline(xmin, ymax-2*dy+1, xmax-2*dx+1, ymin);
+	fdrawline(x1, y2-2*dy+1, x2-2*dx+1, y1);
 }
 
 
@@ -451,7 +446,6 @@ void ED_area_headerprint(ScrArea *sa, const char *str)
 /* ************************************************************ */
 
 
-#define AZONESPOT		12
 static void area_azone_initialize(ScrArea *sa) 
 {
 	AZone *az;
@@ -465,8 +459,8 @@ static void area_azone_initialize(ScrArea *sa)
 	az->type= AZONE_AREA;
 	az->x1= sa->totrct.xmin;
 	az->y1= sa->totrct.ymin;
-	az->x2= sa->totrct.xmin + AZONESPOT-1;
+	az->x2= sa->totrct.xmin + AZONESPOT;
-	az->y2= sa->totrct.ymin + AZONESPOT-1;
+	az->y2= sa->totrct.ymin + AZONESPOT;
 	BLI_init_rcti(&az->rect, az->x1, az->x2, az->y1, az->y2);
 	
 	az= (AZone *)MEM_callocN(sizeof(AZone), "actionzone");
@@ -474,13 +468,13 @@ static void area_azone_initialize(ScrArea *sa)
 	az->type= AZONE_AREA;
 	az->x1= sa->totrct.xmax+1;
 	az->y1= sa->totrct.ymax+1;
-	az->x2= sa->totrct.xmax-AZONESPOT+1;
+	az->x2= sa->totrct.xmax-AZONESPOT;
-	az->y2= sa->totrct.ymax-AZONESPOT+1;
+	az->y2= sa->totrct.ymax-AZONESPOT;
 	BLI_init_rcti(&az->rect, az->x1, az->x2, az->y1, az->y2);
 }
 
 #define AZONEPAD_EDGE	4
-#define AZONEPAD_ICON	8
+#define AZONEPAD_ICON	9
 static void region_azone_edge(AZone *az, ARegion *ar)
 {
 	switch(az->edge) {

source/blender/editors/screen/screen_intern.h

@@ -32,6 +32,8 @@
 struct wmWindow;
 struct Scene;
 
+#define AZONESPOT		12
+
 /* area.c */
 void		area_copy_data	(ScrArea *sa1, ScrArea *sa2, int swap_space);
 

source/blender/editors/screen/screen_ops.c

@@ -474,7 +474,10 @@ AZone *is_in_area_actionzone(ScrArea *sa, int x, int y)
 	for(az= sa->actionzones.first; az; az= az->next) {
 		if(BLI_in_rcti(&az->rect, x, y)) {
 			if(az->type == AZONE_AREA) {
-				if(isect_point_tri_v2_int(az->x1, az->y1, az->x2, az->y2, x, y)) 
+				/* no triangle intersect but a hotspot circle based on corner */
+				int radius= (x-az->x1)*(x-az->x1) + (y-az->y1)*(y-az->y1);
+				
+				if(radius <= AZONESPOT*AZONESPOT)
 					break;
 			}
 			else if(az->type == AZONE_REGION) {

source/blender/makesdna/DNA_constraint_types.h

@@ -699,7 +699,8 @@ typedef enum eChildOf_Flags {
 	CHILDOF_ROTZ	= (1<<5),
 	CHILDOF_SIZEX	= (1<<6),
 	CHILDOF_SIZEY	= (1<<7),
-	CHILDOF_SIZEZ	= (1<<8)
+	CHILDOF_SIZEZ	= (1<<8),
+	CHILDOF_ALL		= 511
 } eChildOf_Flags;
 
 /* Pivot Constraint */