From 5a5ed17c30e24c994c51c11078a533f0937c5de5 Mon Sep 17 00:00:00 2001
From: Ivan Mahonin <bh@icystar.com>
Date: May 01 2023 07:52:44 +0000
Subject: #assistants: tglDrawDoubleSegment


---

diff --git a/toonz/sources/common/tgl/tgl.cpp b/toonz/sources/common/tgl/tgl.cpp
index 88c6989..705c47a 100644
--- a/toonz/sources/common/tgl/tgl.cpp
+++ b/toonz/sources/common/tgl/tgl.cpp
@@ -123,6 +123,34 @@ void tglDrawSegment(const TPointD &p1, const TPointD &p2) {
 
 //-----------------------------------------------------------------------------
 
+void tglDrawDoubleSegment(const TPointD &p1, const TPointD &p2) {
+  double color[4] = {};
+  double width = 1.0;
+  glGetDoublev(GL_CURRENT_COLOR, color);
+  glGetDoublev(GL_LINE_WIDTH, &width);
+  if (width < 1.0) width = 1.0;
+
+  TPointD d = p2 - p1;
+  double k = sqrt(d.x*d.x + d.y*d.y);
+  if (k <= 1e-9) return;
+  k = 0.5*width/k;
+  TPointD offset(-k*d.y, k*d.x);
+
+  glColor4d(1.0 - color[0], 1.0 - color[1], 1.0 - color[2], color[3]);
+  glBegin(GL_LINES);
+  tglVertex(p1 - offset);
+  tglVertex(p2 - offset);
+  glEnd();
+
+  glColor4dv(color);
+  glBegin(GL_LINES);
+  tglVertex(p1 + offset);
+  tglVertex(p2 + offset);
+  glEnd();
+}
+
+//-----------------------------------------------------------------------------
+
 void tglDrawCircle(const TPointD &center, double radius) {
   if (radius <= 0) return;
 
diff --git a/toonz/sources/include/tgl.h b/toonz/sources/include/tgl.h
index 5c993b1..67435ea 100644
--- a/toonz/sources/include/tgl.h
+++ b/toonz/sources/include/tgl.h
@@ -141,6 +141,11 @@ DVAPI void tglDrawDisk(const TPointD &c, double r);
  */
 DVAPI void tglDrawSegment(const TPointD &p1, const TPointD &p2);
 
+/*!
+ Draw a segment pair - positive and negative.
+ */
+DVAPI void tglDrawDoubleSegment(const TPointD &p1, const TPointD &p2);
+
 inline void tglDrawSegment(const TPoint &p1, const TPoint &p2) {
   tglDrawSegment(convert(p1), convert(p2));
 }