Qt 5.6 | Qt OpenGL | Cube OpenGL ES 2.0 example | mainwidget.cpp Example File

Qt 5.6.2 Reference Documentation

# mainwidget.cpp Example File

cube/mainwidget.cpp

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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);
      }