1 files changed, 72 insertions, 0 deletions
diff --git a/demos/opengl/trackball.cpp b/demos/opengl/trackball.cpp
new file mode 100644
index 000000000..f66243d0d
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+++ b/demos/opengl/trackball.cpp
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+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra. Eigen itself is part of the KDE project.
+//
+// Copyright (C) 2008 Gael Guennebaud <g.gael@free.fr>
+//
+// Eigen 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.
+//
+// Alternatively, you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation; either version 2 of
+// the License, or (at your option) any later version.
+//
+// Eigen 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 or the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License and a copy of the GNU General Public License along with
+// Eigen. If not, see <http://www.gnu.org/licenses/>.
+
+#include "trackball.h"
+#include "camera.h"
+
+using namespace Eigen;
+
+void Trackball::track(const Vector2i& newPoint2D)
+{
+  if (mpCamera==0)
+    return;
+  Vector3f newPoint3D;
+  bool newPointOk = mapToSphere(newPoint2D, newPoint3D);
+
+  if (mLastPointOk && newPointOk)
+  {
+    Vector3f axis = mLastPoint3D.cross(newPoint3D).normalized();
+    float cos_angle = mLastPoint3D.dot(newPoint3D);
+    if ( ei_abs(cos_angle) < 1.0 )
+    {
+      float angle = 2.0 * acos(cos_angle);
+      mpCamera->rotateAroundTarget(Quaternionf(AngleAxisf(angle, axis)));
+    }
+  }
+
+  mLastPoint2D = newPoint2D;
+  mLastPoint3D = newPoint3D;
+  mLastPointOk = newPointOk;
+}
+
+bool Trackball::mapToSphere(const Vector2i& p2, Vector3f& v3)
+{
+  if ((p2.x() >= 0) && (p2.x() <= int(mpCamera->vpWidth())) &&
+      (p2.y() >= 0) && (p2.y() <= int(mpCamera->vpHeight())) )
+  {
+    double x  = (double)(p2.x() - 0.5*mpCamera->vpWidth())  / (double)mpCamera->vpWidth();
+    double y  = (double)(0.5*mpCamera->vpHeight() - p2.y()) / (double)mpCamera->vpHeight();
+    double sinx         = sin(M_PI * x * 0.5);
+    double siny         = sin(M_PI * y * 0.5);
+    double sinx2siny2   = sinx * sinx + siny * siny;
+
+    v3.x() = sinx;
+    v3.y() = siny;
+    v3.z() = sinx2siny2 < 1.0 ? sqrt(1.0 - sinx2siny2) : 0.0;
+
+    return true;
+  }
+  else
+    return false;
+}