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<h1 class="title">mainwidget.cpp Example File</h1>
<span class="subtitle">cube/mainwidget.cpp</span>
<!-- $$$cube/mainwidget.cpp-description -->
<div class="descr"> <a name="details"></a>
<pre class="cpp">

  <span class="comment">/****************************************************************************
  **
  ** Copyright (C) 2016 The Qt Company Ltd.
  ** Contact: https://www.qt.io/licensing/
  **
  ** This file is part of the QtCore module of the Qt Toolkit.
  **
  ** $QT_BEGIN_LICENSE:BSD$
  ** Commercial License Usage
  ** Licensees holding valid commercial Qt licenses may use this file in
  ** accordance with the commercial license agreement provided with the
  ** Software or, alternatively, in accordance with the terms contained in
  ** a written agreement between you and The Qt Company. For licensing terms
  ** and conditions see https://www.qt.io/terms-conditions. For further
  ** information use the contact form at https://www.qt.io/contact-us.
  **
  ** BSD License Usage
  ** Alternatively, you may use this file under the terms of the BSD license
  ** as follows:
  **
  ** &quot;Redistribution and use in source and binary forms, with or without
  ** modification, are permitted provided that the following conditions are
  ** met:
  **   * Redistributions of source code must retain the above copyright
  **     notice, this list of conditions and the following disclaimer.
  **   * Redistributions in binary form must reproduce the above copyright
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  **   * Neither the name of The Qt Company Ltd nor the names of its
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  ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.&quot;
  **
  ** $QT_END_LICENSE$
  **
  ****************************************************************************/</span>

  <span class="preprocessor">#include &quot;mainwidget.h&quot;</span>

  <span class="preprocessor">#include &lt;QMouseEvent&gt;</span>

  <span class="preprocessor">#include &lt;math.h&gt;</span>

  MainWidget<span class="operator">::</span>MainWidget(<span class="type"><a href="../qtwidgets/qwidget.html">QWidget</a></span> <span class="operator">*</span>parent) :
      <span class="type"><a href="../qtwidgets/qopenglwidget.html">QOpenGLWidget</a></span>(parent)<span class="operator">,</span>
      geometries(<span class="number">0</span>)<span class="operator">,</span>
      texture(<span class="number">0</span>)<span class="operator">,</span>
      angularSpeed(<span class="number">0</span>)
  {
  }

  MainWidget<span class="operator">::</span><span class="operator">~</span>MainWidget()
  {
      <span class="comment">// Make sure the context is current when deleting the texture</span>
      <span class="comment">// and the buffers.</span>
      makeCurrent();
      <span class="keyword">delete</span> texture;
      <span class="keyword">delete</span> geometries;
      doneCurrent();
  }

  <span class="type">void</span> MainWidget<span class="operator">::</span>mousePressEvent(<span class="type"><a href="../qtgui/qmouseevent.html">QMouseEvent</a></span> <span class="operator">*</span>e)
  {
      <span class="comment">// Save mouse press position</span>
      mousePressPosition <span class="operator">=</span> QVector2D(e<span class="operator">-</span><span class="operator">&gt;</span>localPos());
  }

  <span class="type">void</span> MainWidget<span class="operator">::</span>mouseReleaseEvent(<span class="type"><a href="../qtgui/qmouseevent.html">QMouseEvent</a></span> <span class="operator">*</span>e)
  {
      <span class="comment">// Mouse release position - mouse press position</span>
      QVector2D diff <span class="operator">=</span> QVector2D(e<span class="operator">-</span><span class="operator">&gt;</span>localPos()) <span class="operator">-</span> mousePressPosition;

      <span class="comment">// Rotation axis is perpendicular to the mouse position difference</span>
      <span class="comment">// vector</span>
      QVector3D n <span class="operator">=</span> QVector3D(diff<span class="operator">.</span>y()<span class="operator">,</span> diff<span class="operator">.</span>x()<span class="operator">,</span> <span class="number">0.0</span>)<span class="operator">.</span>normalized();

      <span class="comment">// Accelerate angular speed relative to the length of the mouse sweep</span>
      <span class="type"><a href="../qtcore/qtglobal.html#qreal-typedef">qreal</a></span> acc <span class="operator">=</span> diff<span class="operator">.</span>length() <span class="operator">/</span> <span class="number">100.0</span>;

      <span class="comment">// Calculate new rotation axis as weighted sum</span>
      rotationAxis <span class="operator">=</span> (rotationAxis <span class="operator">*</span> angularSpeed <span class="operator">+</span> n <span class="operator">*</span> acc)<span class="operator">.</span>normalized();

      <span class="comment">// Increase angular speed</span>
      angularSpeed <span class="operator">+</span><span class="operator">=</span> acc;
  }

  <span class="type">void</span> MainWidget<span class="operator">::</span>timerEvent(<span class="type"><a href="../qtcore/qtimerevent.html">QTimerEvent</a></span> <span class="operator">*</span>)
  {
      <span class="comment">// Decrease angular speed (friction)</span>
      angularSpeed <span class="operator">*</span><span class="operator">=</span> <span class="number">0.99</span>;

      <span class="comment">// Stop rotation when speed goes below threshold</span>
      <span class="keyword">if</span> (angularSpeed <span class="operator">&lt;</span> <span class="number">0.01</span>) {
          angularSpeed <span class="operator">=</span> <span class="number">0.0</span>;
      } <span class="keyword">else</span> {
          <span class="comment">// Update rotation</span>
          rotation <span class="operator">=</span> <span class="type"><a href="../qtgui/qquaternion.html">QQuaternion</a></span><span class="operator">::</span>fromAxisAndAngle(rotationAxis<span class="operator">,</span> angularSpeed) <span class="operator">*</span> rotation;

          <span class="comment">// Request an update</span>
          update();
      }
  }

  <span class="type">void</span> MainWidget<span class="operator">::</span>initializeGL()
  {
      initializeOpenGLFunctions();

      glClearColor(<span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">1</span>);

      initShaders();
      initTextures();

      <span class="comment">// Enable depth buffer</span>
      glEnable(GL_DEPTH_TEST);

      <span class="comment">// Enable back face culling</span>
      glEnable(GL_CULL_FACE);

      geometries <span class="operator">=</span> <span class="keyword">new</span> GeometryEngine;

      <span class="comment">// Use QBasicTimer because its faster than QTimer</span>
      timer<span class="operator">.</span>start(<span class="number">12</span><span class="operator">,</span> <span class="keyword">this</span>);
  }

  <span class="type">void</span> MainWidget<span class="operator">::</span>initShaders()
  {
      <span class="comment">// Compile vertex shader</span>
      <span class="keyword">if</span> (<span class="operator">!</span>program<span class="operator">.</span>addShaderFromSourceFile(<span class="type"><a href="../qtgui/qopenglshader.html">QOpenGLShader</a></span><span class="operator">::</span>Vertex<span class="operator">,</span> <span class="string">&quot;:/vshader.glsl&quot;</span>))
          close();

      <span class="comment">// Compile fragment shader</span>
      <span class="keyword">if</span> (<span class="operator">!</span>program<span class="operator">.</span>addShaderFromSourceFile(<span class="type"><a href="../qtgui/qopenglshader.html">QOpenGLShader</a></span><span class="operator">::</span>Fragment<span class="operator">,</span> <span class="string">&quot;:/fshader.glsl&quot;</span>))
          close();

      <span class="comment">// Link shader pipeline</span>
      <span class="keyword">if</span> (<span class="operator">!</span>program<span class="operator">.</span>link())
          close();

      <span class="comment">// Bind shader pipeline for use</span>
      <span class="keyword">if</span> (<span class="operator">!</span>program<span class="operator">.</span>bind())
          close();
  }

  <span class="type">void</span> MainWidget<span class="operator">::</span>initTextures()
  {
      <span class="comment">// Load cube.png image</span>
      texture <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="../qtgui/qopengltexture.html">QOpenGLTexture</a></span>(<span class="type"><a href="../qtgui/qimage.html">QImage</a></span>(<span class="string">&quot;:/cube.png&quot;</span>)<span class="operator">.</span>mirrored());

      <span class="comment">// Set nearest filtering mode for texture minification</span>
      texture<span class="operator">-</span><span class="operator">&gt;</span>setMinificationFilter(<span class="type"><a href="../qtgui/qopengltexture.html">QOpenGLTexture</a></span><span class="operator">::</span>Nearest);

      <span class="comment">// Set bilinear filtering mode for texture magnification</span>
      texture<span class="operator">-</span><span class="operator">&gt;</span>setMagnificationFilter(<span class="type"><a href="../qtgui/qopengltexture.html">QOpenGLTexture</a></span><span class="operator">::</span>Linear);

      <span class="comment">// Wrap texture coordinates by repeating</span>
      <span class="comment">// f.ex. texture coordinate (1.1, 1.2) is same as (0.1, 0.2)</span>
      texture<span class="operator">-</span><span class="operator">&gt;</span>setWrapMode(<span class="type"><a href="../qtgui/qopengltexture.html">QOpenGLTexture</a></span><span class="operator">::</span>Repeat);
  }

  <span class="type">void</span> MainWidget<span class="operator">::</span>resizeGL(<span class="type">int</span> w<span class="operator">,</span> <span class="type">int</span> h)
  {
      <span class="comment">// Calculate aspect ratio</span>
      <span class="type"><a href="../qtcore/qtglobal.html#qreal-typedef">qreal</a></span> aspect <span class="operator">=</span> <span class="type"><a href="../qtcore/qtglobal.html#qreal-typedef">qreal</a></span>(w) <span class="operator">/</span> <span class="type"><a href="../qtcore/qtglobal.html#qreal-typedef">qreal</a></span>(h <span class="operator">?</span> h : <span class="number">1</span>);

      <span class="comment">// Set near plane to 3.0, far plane to 7.0, field of view 45 degrees</span>
      <span class="keyword">const</span> <span class="type"><a href="../qtcore/qtglobal.html#qreal-typedef">qreal</a></span> zNear <span class="operator">=</span> <span class="number">3.0</span><span class="operator">,</span> zFar <span class="operator">=</span> <span class="number">7.0</span><span class="operator">,</span> fov <span class="operator">=</span> <span class="number">45.0</span>;

      <span class="comment">// Reset projection</span>
      projection<span class="operator">.</span>setToIdentity();

      <span class="comment">// Set perspective projection</span>
      projection<span class="operator">.</span>perspective(fov<span class="operator">,</span> aspect<span class="operator">,</span> zNear<span class="operator">,</span> zFar);
  }

  <span class="type">void</span> MainWidget<span class="operator">::</span>paintGL()
  {
      <span class="comment">// Clear color and depth buffer</span>
      glClear(GL_COLOR_BUFFER_BIT <span class="operator">|</span> GL_DEPTH_BUFFER_BIT);

      texture<span class="operator">-</span><span class="operator">&gt;</span>bind();

      <span class="comment">// Calculate model view transformation</span>
      QMatrix4x4 matrix;
      matrix<span class="operator">.</span>translate(<span class="number">0.0</span><span class="operator">,</span> <span class="number">0.0</span><span class="operator">,</span> <span class="operator">-</span><span class="number">5.0</span>);
      matrix<span class="operator">.</span>rotate(rotation);

      <span class="comment">// Set modelview-projection matrix</span>
      program<span class="operator">.</span>setUniformValue(<span class="string">&quot;mvp_matrix&quot;</span><span class="operator">,</span> projection <span class="operator">*</span> matrix);

      <span class="comment">// Use texture unit 0 which contains cube.png</span>
      program<span class="operator">.</span>setUniformValue(<span class="string">&quot;texture&quot;</span><span class="operator">,</span> <span class="number">0</span>);

      <span class="comment">// Draw cube geometry</span>
      geometries<span class="operator">-</span><span class="operator">&gt;</span>drawCubeGeometry(<span class="operator">&amp;</span>program);
  }

</pre>
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<!-- @@@cube/mainwidget.cpp -->
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