--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/OrthancStone/Sources/Scene2D/Internals/OpenGLArrowRenderer.cpp	Fri Oct 30 16:26:39 2020 +0100
@@ -0,0 +1,134 @@
+/**
+ * Stone of Orthanc
+ * Copyright (C) 2012-2016 Sebastien Jodogne, Medical Physics
+ * Department, University Hospital of Liege, Belgium
+ * Copyright (C) 2017-2020 Osimis S.A., Belgium
+ *
+ * This program is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program. If not, see
+ * <http://www.gnu.org/licenses/>.
+ **/
+
+
+#include "OpenGLArrowRenderer.h"
+
+#include <OrthancException.h>
+
+#include <math.h>
+
+
+namespace OrthancStone
+{
+  namespace Internals
+  {
+    void OpenGLArrowRenderer::LoadLayer(const ArrowSceneLayer& layer)
+    {
+      // "dataBody_" contains the "body" of the arrow, in scene coordinates
+      {
+        PolylineSceneLayer l;
+        l.SetThickness(layer.GetThickness());
+
+        PolylineSceneLayer::Chain chain;
+        chain.push_back(layer.GetA());
+        chain.push_back(layer.GetB());
+        l.AddChain(chain, false, layer.GetColor());
+
+        dataBody_.reset(new OpenGLLinesProgram::Data(context_, l));
+      }
+
+      // "dataHead_" contains the "head" of the arrow, properly scaled in
+      // pixel coordinates, but with center at (0,0)
+      {
+        PolylineSceneLayer l;
+        l.SetThickness(layer.GetThickness());
+
+        const double c = cos(layer.GetArrowAngle());
+        const double s = sin(layer.GetArrowAngle());
+        
+        PolylineSceneLayer::Chain chain;
+        chain.push_back(ScenePoint2D(c, s) * layer.GetArrowLength());
+        chain.push_back(ScenePoint2D(0, 0));
+        chain.push_back(ScenePoint2D(c, -s) * layer.GetArrowLength());
+        l.AddChain(chain, false, layer.GetColor());
+
+        dataHead_.reset(new OpenGLLinesProgram::Data(context_, l));
+      }
+
+      // Compute a unit vector encoding the direction of the body of the arrow
+      ScenePoint2D direction = layer.GetB() - layer.GetA();
+      double n = ScenePoint2D::SquaredMagnitude(direction);
+      if (LinearAlgebra::IsCloseToZero(n))
+      {
+        direction = ScenePoint2D(1, 0);
+      }
+      else
+      {
+        direction = direction / sqrt(n);
+      }
+
+      // Compute a rotation matrix, to bring the "head" in the axis of the "body"
+      // https://math.stackexchange.com/a/3565068
+      Matrix rotation = LinearAlgebra::ZeroMatrix(3, 3);
+      rotation(0, 0) = direction.GetX();
+      rotation(1, 0) = direction.GetY();
+      rotation(0, 1) = -direction.GetY();
+      rotation(1, 1) = direction.GetX();
+      rotation(2, 2) = 1;
+
+      transformHead_ = AffineTransform2D::Combine(
+        AffineTransform2D::CreateOffset(layer.GetA().GetX(), layer.GetA().GetY()),
+        AffineTransform2D(rotation));
+        
+      if (dataBody_.get() == NULL ||
+          dataHead_.get() == NULL)
+      {
+        throw Orthanc::OrthancException(Orthanc::ErrorCode_InternalError);
+      }
+    }
+
+
+    OpenGLArrowRenderer::OpenGLArrowRenderer(OpenGL::IOpenGLContext& context,
+                                             OpenGLLinesProgram& program,
+                                             const ArrowSceneLayer& layer) :
+      context_(context),
+      program_(program)
+    {
+      LoadLayer(layer);
+    }
+
+
+    void OpenGLArrowRenderer::Render(const AffineTransform2D& transform,
+                                     unsigned int canvasWidth,
+                                     unsigned int canvasHeight)
+    {
+      if (!context_.IsContextLost())
+      {
+        program_.Apply(*dataBody_, transform, canvasWidth, canvasHeight, true, true);
+
+        const double z = 1.0 / transform.ComputeZoom();
+        const AffineTransform2D t2 = AffineTransform2D::Combine(
+          transform,       // 3. Apply the original transform
+          transformHead_,  // 2. Bring the "head" of the arrow at the proper position/angle          
+          AffineTransform2D::CreateScaling(z, z));  // 1. Neutralize the zoom level
+
+        program_.Apply(*dataHead_, t2, canvasWidth, canvasHeight, true, true);
+      }
+    }
+
+
+    void OpenGLArrowRenderer::Update(const ISceneLayer& layer) 
+    {
+      LoadLayer(dynamic_cast<const ArrowSceneLayer&>(layer));
+    }
+  }
+}