New "Maintain Volume" constraint. When attached to a bone, you specify a "free" axis. Upon scaling, this free axis scales normally, but the constraint forces the other two axes to adjust themselves appropriately so that overall bone volume is maintained. So, setting "Y" as the free axis (the default) creates a bone that automatically squashes and stretches when scaling. Thanks to Aligorith, Fweeb, Cessen and others for the feedback.

1 files changed, 14 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_constraint_types.h b/source/blender/makesdna/DNA_constraint_types.h
index 6e837588f0c..358cbb6e34c 100644
--- a/source/blender/makesdna/DNA_constraint_types.h
+++ b/source/blender/makesdna/DNA_constraint_types.h
@@ -208,6 +208,12 @@ typedef struct bSizeLikeConstraint {
 	char		subtarget[32];
 } bSizeLikeConstraint;
 
+/* Maintain Volume Constraint */
+typedef struct bSameVolumeConstraint {
+	int		flag;
+	float 		volume;
+} bSameVolumeConstraint;
+
 /* Copy Transform Constraint */
 typedef struct bTransLikeConstraint {
 	Object 		*tar;
@@ -412,6 +418,7 @@ typedef enum eBConstraint_Types {
 	CONSTRAINT_TYPE_DAMPTRACK,			/* New Tracking constraint that minimises twisting */
 	CONSTRAINT_TYPE_SPLINEIK,			/* Spline-IK - Align 'n' bones to a curve */
 	CONSTRAINT_TYPE_TRANSLIKE,			/* Copy transform matrix */
+	CONSTRAINT_TYPE_SAMEVOL,			/* Maintain volume during scaling */
 	
 	/* NOTE: no constraints are allowed to be added after this */
 	NUM_CONSTRAINT_TYPES
@@ -499,6 +506,13 @@ typedef enum eCopyScale_Flags {
 	SIZELIKE_OFFSET = (1<<3),
 } eCopyScale_Flags;
 
+/* bSameVolumeConstraint.flag */
+typedef enum eSameVolume_Modes {
+	SAMEVOL_X		= 0,
+	SAMEVOL_Y,
+	SAMEVOL_Z, 
+} eSameVolume_Modes;
+
 /* Locked-Axis Values (Locked Track) */
 typedef enum eLockAxis_Modes {
 	LOCK_X	= 0,