From d212df22ff2f802a770cf6753b649a4b10d45448 Mon Sep 17 00:00:00 2001
From: Eric Mehl <eric@thinkhypothetical.com>
Date: Tue, 17 Oct 2023 12:09:10 -0400
Subject: [PATCH] EdgeHandle : Tooltip track edge, not cursor

---
 Changes.md                      |  2 +-
 src/GafferSceneUI/LightTool.cpp | 15 ++++++++++++---
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/Changes.md b/Changes.md
index 00d769df351..f1d2b4969cb 100644
--- a/Changes.md
+++ b/Changes.md
@@ -11,7 +11,7 @@ Features
 Improvements
 ------------
 
-- LightTool : Changed spot light tool tip location so that it follows the cone during drag.
+- LightTool : Changed spot light and quad light edge tool tip locations so that they follow the cone and edge during drag.
 
 Fixes
 -----
diff --git a/src/GafferSceneUI/LightTool.cpp b/src/GafferSceneUI/LightTool.cpp
index 3959afbd277..de87b08b539 100644
--- a/src/GafferSceneUI/LightTool.cpp
+++ b/src/GafferSceneUI/LightTool.cpp
@@ -2044,10 +2044,12 @@ class EdgeHandle : public LightToolHandle
 			m_oppositeScaleAttributeName( oppositeScaleAttributeName ),
 			m_edgeMargin( edgeMargin ),
 			m_tipPlugSuffix( tipPlugSuffix ),
+
 			m_edgeScale( 1.f ),
 			m_oppositeScale( 1.f ),
 			m_orientation(),
-			m_oppositeAdditionalScale( 1.f )
+			m_oppositeAdditionalScale( 1.f ),
+			m_tooltipT( 0 )
 		{
 		}
 
@@ -2234,8 +2236,14 @@ class EdgeHandle : public LightToolHandle
 			edgeSegment.p1 += offset;
 			edgeSegment *= m_orientation;
 
-			V3f eventClosest;
-			setTooltipPosition( edgeSegment.closestPoints( LineSegment3f( eventLine.p0, eventLine.p1 ), eventClosest ) );
+			if( !m_drag )
+			{
+				V3f eventClosest;
+				const V3f closestPoint = edgeSegment.closestPoints( LineSegment3f( eventLine.p0, eventLine.p1 ), eventClosest );
+				m_tooltipT = ( closestPoint - edgeSegment.p0 ).length() / edgeSegment.length();
+			}
+
+			setTooltipPosition( edgeSegment( m_tooltipT ) );
 		}
 
 	private :
@@ -2307,6 +2315,7 @@ class EdgeHandle : public LightToolHandle
 		float m_oppositeScale;
 		M44f m_orientation;
 		float m_oppositeAdditionalScale;
+		float m_tooltipT;  // Parameter `t` along the edge set at the start of the drag
 		std::optional<LinearDrag> m_drag;
 };