Toying a bit with MMB behavior:

MMB click with no constraint selects a constraint right away (the axis selector doesn't flash on screen)
MMB click with a constraint removes the constraint
MMB click-drag in both case (with and without a constraint) uses the axis selector.

stopConstraint didn't remove the CON_SELECT flag, so cancelling transform while selecting a constraint and then reentering transform was funny. Fixed

3 files changed, 22 insertions, 8 deletions

diff --git a/source/blender/include/transform.h b/source/blender/include/transform.h
index 1d42861e07c..23c816053ff 100755
--- a/source/blender/include/transform.h
+++ b/source/blender/include/transform.h
@@ -266,7 +266,7 @@ void stopConstraint(TransInfo *t);
 
 void getConstraintMatrix(TransInfo *t);
 
-void initSelectConstraint(TransInfo *t);
+void initSelectConstraint(TransInfo *t, float mtx[3][3]);
 void selectConstraint(TransInfo *t);
 void postSelectConstraint(TransInfo *t);
 
diff --git a/source/blender/src/transform.c b/source/blender/src/transform.c
index 25011e2f4b4..2c0ee40954c 100755
--- a/source/blender/src/transform.c
+++ b/source/blender/src/transform.c
@@ -134,7 +134,10 @@ void Transform(int mode, int context)
 	short pmval[2] = {0, 0}, mval[2], val;
 	float mati[3][3];
 	unsigned short event;
+	/* constraint mode THIS IS A HACK will have to use con.mode eventually */
 	char cmode = '\0';
+	/* If MMB is pressed or not */
+	char mmb_press = 0;
 
 	/*joeedh -> hopefully may be what makes the old transform() constant*/
 	/* ton: I doubt, but it doesnt harm for now. shouldnt be needed though */
@@ -226,6 +229,9 @@ void Transform(int mode, int context)
 		getmouseco_areawin(mval);
 		
 		if (mval[0] != pmval[0] || mval[1] != pmval[1]) {
+			if (mmb_press) {
+				initSelectConstraint(&Trans, mati);
+			}
 			Trans.redraw = 1;
 		}
 		if (Trans.redraw) {
@@ -272,10 +278,18 @@ void Transform(int mode, int context)
 								initTrackball(&Trans);
 							}
 						}
-						else 
-							initSelectConstraint(&Trans);
+						else {
+							mmb_press = 1;
+							if (Trans.con.mode & CON_APPLY) {
+								stopConstraint(&Trans);
+							}
+							else {
+								initSelectConstraint(&Trans, mati);
+								postSelectConstraint(&Trans);
+							}
+						}
+						Trans.redraw = 1;
 					}
-					Trans.redraw = 1;
 					break;
 				case ESCKEY:
 				case RIGHTMOUSE:
@@ -433,6 +447,7 @@ void Transform(int mode, int context)
 				   after releasing modifer key */
 				case MIDDLEMOUSE:
 					if ((Trans.flag & T_NO_CONSTRAINT)==0) {
+						mmb_press = 0;
 						postSelectConstraint(&Trans);
 						Trans.redraw = 1;
 					}
diff --git a/source/blender/src/transform_constraints.c b/source/blender/src/transform_constraints.c
index 6908e6c8f96..7611041cddd 100755
--- a/source/blender/src/transform_constraints.c
+++ b/source/blender/src/transform_constraints.c
@@ -718,7 +718,7 @@ void startConstraint(TransInfo *t) {
 }
 
 void stopConstraint(TransInfo *t) {
-	t->con.mode &= ~CON_APPLY;
+	t->con.mode &= ~(CON_APPLY|CON_SELECT);
 	*t->con.text = '\0';
 	t->num.idx_max = t->idx_max;
 }
@@ -751,10 +751,9 @@ void getConstraintMatrix(TransInfo *t)
 	Mat3MulMat3(t->con.pmtx, t->con.mtx, mat);
 }
 
-void initSelectConstraint(TransInfo *t)
+void initSelectConstraint(TransInfo *t, float mtx[3][3])
 {
-	Mat3One(t->con.mtx);
-	Mat3One(t->con.pmtx);
+	Mat3CpyMat3(t->con.mtx, mtx);
 	t->con.mode |= CON_APPLY;
 	t->con.mode |= CON_SELECT;