mainwidget.cpp Example File

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  #include "mainwidget.h"

  #include <QMouseEvent>

  #include <math.h>

  MainWidget::MainWidget(QWidget *parent) :
      QOpenGLWidget(parent),
      geometries(0),
      texture(0),
      angularSpeed(0)
  {
  }

  MainWidget::~MainWidget()
  {
      // Make sure the context is current when deleting the texture
      // and the buffers.
      makeCurrent();
      delete texture;
      delete geometries;
      doneCurrent();
  }

  void MainWidget::mousePressEvent(QMouseEvent *e)
  {
      // Save mouse press position
      mousePressPosition = QVector2D(e->localPos());
  }

  void MainWidget::mouseReleaseEvent(QMouseEvent *e)
  {
      // Mouse release position - mouse press position
      QVector2D diff = QVector2D(e->localPos()) - mousePressPosition;

      // Rotation axis is perpendicular to the mouse position difference
      // vector
      QVector3D n = QVector3D(diff.y(), diff.x(), 0.0).normalized();

      // Accelerate angular speed relative to the length of the mouse sweep
      qreal acc = diff.length() / 100.0;

      // Calculate new rotation axis as weighted sum
      rotationAxis = (rotationAxis * angularSpeed + n * acc).normalized();

      // Increase angular speed
      angularSpeed += acc;
  }

  void MainWidget::timerEvent(QTimerEvent *)
  {
      // Decrease angular speed (friction)
      angularSpeed *= 0.99;

      // Stop rotation when speed goes below threshold
      if (angularSpeed < 0.01) {
          angularSpeed = 0.0;
      } else {
          // Update rotation
          rotation = QQuaternion::fromAxisAndAngle(rotationAxis, angularSpeed) * rotation;

          // Request an update
          update();
      }
  }

  void MainWidget::initializeGL()
  {
      initializeOpenGLFunctions();

      glClearColor(0, 0, 0, 1);

      initShaders();
      initTextures();

      // Enable depth buffer
      glEnable(GL_DEPTH_TEST);

      // Enable back face culling
      glEnable(GL_CULL_FACE);

      geometries = new GeometryEngine;

      // Use QBasicTimer because its faster than QTimer
      timer.start(12, this);
  }

  void MainWidget::initShaders()
  {
      // Compile vertex shader
      if (!program.addShaderFromSourceFile(QOpenGLShader::Vertex, ":/vshader.glsl"))
          close();

      // Compile fragment shader
      if (!program.addShaderFromSourceFile(QOpenGLShader::Fragment, ":/fshader.glsl"))
          close();

      // Link shader pipeline
      if (!program.link())
          close();

      // Bind shader pipeline for use
      if (!program.bind())
          close();
  }

  void MainWidget::initTextures()
  {
      // Load cube.png image
      texture = new QOpenGLTexture(QImage(":/cube.png").mirrored());

      // Set nearest filtering mode for texture minification
      texture->setMinificationFilter(QOpenGLTexture::Nearest);

      // Set bilinear filtering mode for texture magnification
      texture->setMagnificationFilter(QOpenGLTexture::Linear);

      // Wrap texture coordinates by repeating
      // f.ex. texture coordinate (1.1, 1.2) is same as (0.1, 0.2)
      texture->setWrapMode(QOpenGLTexture::Repeat);
  }

  void MainWidget::resizeGL(int w, int h)
  {
      // Calculate aspect ratio
      qreal aspect = qreal(w) / qreal(h ? h : 1);

      // Set near plane to 3.0, far plane to 7.0, field of view 45 degrees
      const qreal zNear = 3.0, zFar = 7.0, fov = 45.0;

      // Reset projection
      projection.setToIdentity();

      // Set perspective projection
      projection.perspective(fov, aspect, zNear, zFar);
  }

  void MainWidget::paintGL()
  {
      // Clear color and depth buffer
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

      texture->bind();

      // Calculate model view transformation
      QMatrix4x4 matrix;
      matrix.translate(0.0, 0.0, -5.0);
      matrix.rotate(rotation);

      // Set modelview-projection matrix
      program.setUniformValue("mvp_matrix", projection * matrix);

      // Use texture unit 0 which contains cube.png
      program.setUniformValue("texture", 0);

      // Draw cube geometry
      geometries->drawCubeGeometry(&program);
  }