STORM-1920: Documented the meaning of some of the variables involved, built simplest change to solve issue.

The highlighting code assumed that the axis of the scaling movement was aligned with the scale tick marks - e.g. one of the cardinal directions with respect to the OBB of the selection.  This was and is NOT true when dragging from the corner, aka scaling more than one axis at a time.  The solution was to calculate the measured distance by projecting the snapped distance along the snap direction onto the axis of the relevant snap guide.  This gives the correct values, and is nice and clean - both in the change involved, and in the values returned.

However, while the fundamental misunderstanding in the code has been cleaned up by this change, the tick_val variable has so much jitter in the bottom end that the is_approx_equal function doesn’t come true > 98% of the time.  This is the next problem to solve.

2 files changed, 13 insertions, 12 deletions

diff --git a/indra/newview/llmanipscale.cpp b/indra/newview/llmanipscale.cpp
index 087f617bbb..18201f9074 100755
--- a/indra/newview/llmanipscale.cpp
+++ b/indra/newview/llmanipscale.cpp
@@ -870,7 +870,7 @@ void LLManipScale::dragCorner( S32 x, S32 y )
 	}
 	mDragPointGlobal = lerp(mDragStartCenterGlobal, mDragStartPointGlobal, t);
 
-	LLBBox bbox	     = LLSelectMgr::getInstance()->getBBoxOfSelection();
+	LLBBox bbox      = LLSelectMgr::getInstance()->getBBoxOfSelection();
 	F32 scale_factor = 1.f;
 	F32 max_scale    = partToMaxScale(mManipPart, bbox);
 	F32 min_scale    = partToMinScale(mManipPart, bbox);
@@ -888,9 +888,6 @@ void LLManipScale::dragCorner( S32 x, S32 y )
 	LLVector3 projected_drag_pos1 = inverse_projected_vec(mScaleDir, orthogonal_component(mouse_on_plane1, mSnapGuideDir1));
 	LLVector3 projected_drag_pos2 = inverse_projected_vec(mScaleDir, orthogonal_component(mouse_on_plane2, mSnapGuideDir2));
 
-	LLVector3 mouse_offset_from_scale_line_1 = orthogonal_component(mouse_on_plane1, mScaleDir);
-	LLVector3 mouse_offset_from_scale_line_2 = orthogonal_component(mouse_on_plane2, mScaleDir);
-
 	BOOL snap_enabled = gSavedSettings.getBOOL("SnapEnabled");
 	if (snap_enabled && (mouse_on_plane1 - projected_drag_pos1) * mSnapGuideDir1 > mSnapRegimeOffset)
 	{
@@ -1729,7 +1726,9 @@ void LLManipScale::renderSnapGuides(const LLBBox& bbox)
 
 				F32 text_highlight = 0.8f;
 
-				if (is_approx_equal(tick_val, mScaleSnapValue) && mInSnapRegime)
+				F32 measured_distance = -(mSnapGuideDir2 * (mScaleDir * mScaleSnapValue)); // The other snap guide points down the vector we are measuring against, which when the snapvalue along the scale direction is projected against gives the distance along the relevant axis of measurement.
+
+				if (is_approx_equal(tick_val, measured_distance) && mInSnapRegime)
 				{
 					text_highlight = 1.f;
 				}
@@ -1781,7 +1780,9 @@ void LLManipScale::renderSnapGuides(const LLBBox& bbox)
 
 					F32 text_highlight = 0.8f;
 
-					if (is_approx_equal(tick_val, mScaleSnapValue) && mInSnapRegime)
+					F32 measured_distance = -(mSnapGuideDir1 * (mScaleDir * mScaleSnapValue)); // The other snap guide points down the vector we are measuring against, which when the snapvalue along the scale direction is projected against gives the distance along the relevant axis of measurement.
+
+					if (is_approx_equal(tick_val, measured_distance) && mInSnapRegime)
 					{
 						text_highlight = 1.f;
 					}
diff --git a/indra/newview/llmanipscale.h b/indra/newview/llmanipscale.h
index 5cb8898fd0..652b90d59e 100755
--- a/indra/newview/llmanipscale.h
+++ b/indra/newview/llmanipscale.h
@@ -148,10 +148,10 @@ private:
 	typedef std::set<ManipulatorHandle*, compare_manipulators> minpulator_list_t;
 	minpulator_list_t mProjectedManipulators;
 	LLVector4		mManipulatorVertices[14];
-	F32				mScaleSnapUnit1;  // size of snap multiples for axis 1
-	F32				mScaleSnapUnit2;  // size of snap multiples for axis 2
-	LLVector3		mScalePlaneNormal1; // normal of plane in which scale occurs that most faces camera
-	LLVector3		mScalePlaneNormal2; // normal of plane in which scale occurs that most faces camera
+	F32				mScaleSnapUnit1;  //!< Size of snap multiples for axis 1.
+	F32				mScaleSnapUnit2;  //!< Size of snap multiples for axis 2.
+	LLVector3		mScalePlaneNormal1; //!< Normal of plane in which scale occurs that most faces camera.
+	LLVector3		mScalePlaneNormal2; //!< Normal of plane in which scale occurs that most faces camera.
 	LLVector3		mSnapGuideDir1;
 	LLVector3		mSnapGuideDir2;
 	LLVector3		mSnapDir1;
@@ -159,8 +159,8 @@ private:
 	F32				mSnapRegimeOffset;
 	F32				mSnapGuideLength;
 	LLVector3		mScaleCenter;
-	LLVector3		mScaleDir;
-	F32				mScaleSnapValue;
+	LLVector3		mScaleDir; //!< The direction of the scaling action.  In face-dragging this is aligned with one of the cardinal axis relative to the prim, but in corner-dragging this is along the diagonal.
+	F32				mScaleSnapValue; //!< The distance of the current position nearest the mouse location, measured along mScaleDir.  Is measured either from the center or from the far face/corner depending upon whether uniform scaling is true or false respectively.
 	BOOL			mInSnapRegime;
 	F32*			mManipulatorScales;
 };