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# mainwidget.cpp Example File

opengl/cube/mainwidget.cpp

     /****************************************************************************
     **
     ** Copyright (C) 2015 The Qt Company Ltd.
     ** Contact: http://www.qt.io/licensing/
     **
     ** This file is part of the QtCore module of the Qt Toolkit.
     **
     ** $QT_BEGIN_LICENSE:BSD$
     ** You may use this file under the terms of the BSD license as follows:
     **
     ** "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
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     **     notice, this list of conditions and the following disclaimer in
     **     the documentation and/or other materials provided with the
     **     distribution.
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     **     contributors may be used to endorse or promote products derived
     **     from this software without specific prior written permission.
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     #include "mainwidget.h"

     #include "geometryengine.h"

     #include <QtOpenGL/QGLShaderProgram>

     #include <QBasicTimer>
     #include <QMouseEvent>
     #include <QDebug>

     #include <math.h>
     #include <locale.h>

     MainWidget::MainWidget(QWidget *parent) :
         QGLWidget(parent),
         timer(new QBasicTimer),
         program(new QGLShaderProgram),
         geometries(new GeometryEngine)
     {
     }

     MainWidget::~MainWidget()
     {
         delete timer; timer = 0;
         delete program; program = 0;
         delete geometries; geometries = 0;

         deleteTexture(texture);
     }

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

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

         // 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;

             // Update scene
             updateGL();
         }
     }

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

         qglClearColor(Qt::black);

         qDebug() << "Initializing shaders...";
         initShaders();

         qDebug() << "Initializing textures...";
         initTextures();

         // Enable depth buffer
         glEnable(GL_DEPTH_TEST);

         // Enable back face culling
         glEnable(GL_CULL_FACE);

         qDebug() << "Initializing geometries...";
         geometries->init();

         // using QBasicTimer because its faster that QTimer
         timer->start(12, this);
     }

     void MainWidget::initShaders()
     {
         // Overriding system locale until shaders are compiled
         setlocale(LC_NUMERIC, "C");

         // Compiling vertex shader
         if (!program->addShaderFromSourceFile(QGLShader::Vertex, ":/vshader.glsl"))
             close();

         // Compiling fragment shader
         if (!program->addShaderFromSourceFile(QGLShader::Fragment, ":/fshader.glsl"))
             close();

         // Linking shader pipeline
         if (!program->link())
             close();

         // Binding shader pipeline for use
         if (!program->bind())
             close();

         // Restore system locale
         setlocale(LC_ALL, "");
     }

     void MainWidget::initTextures()
     {
         // Loading cube.png to texture unit 0
         glActiveTexture(GL_TEXTURE0);
         glEnable(GL_TEXTURE_2D);
         texture = bindTexture(QImage(":/cube.png"));

         // Set nearest filtering mode for texture minification
         glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

         // Set bilinear filtering mode for texture magnification
         glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

         // Wrap texture coordinates by repeating
         // f.ex. texture coordinate (1.1, 1.2) is same as (0.1, 0.2)
         glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
         glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
     }

     void MainWidget::resizeGL(int w, int h)
     {
         // Set OpenGL viewport to cover whole widget
         glViewport(0, 0, w, 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);

         // 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);

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

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