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);
 }