glwidget.cpp Example File

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  #include "glwidget.h"
  #include <QOpenGLShaderProgram>
  #include <QOpenGLTexture>
  #include <QMouseEvent>

  GLWidget::GLWidget(QWidget *parent)
      : QOpenGLWidget(parent),
        clearColor(Qt::black),
        xRot(0),
        yRot(0),
        zRot(0),
        program(0)
  {
      memset(textures, 0, sizeof(textures));
  }

  GLWidget::~GLWidget()
  {
      makeCurrent();
      vbo.destroy();
      for (int i = 0; i < 6; ++i)
          delete textures[i];
      delete program;
      doneCurrent();
  }

  QSize GLWidget::minimumSizeHint() const
  {
      return QSize(50, 50);
  }

  QSize GLWidget::sizeHint() const
  {
      return QSize(200, 200);
  }

  void GLWidget::rotateBy(int xAngle, int yAngle, int zAngle)
  {
      xRot += xAngle;
      yRot += yAngle;
      zRot += zAngle;
      update();
  }

  void GLWidget::setClearColor(const QColor &color)
  {
      clearColor = color;
      update();
  }

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

      makeObject();

      glEnable(GL_DEPTH_TEST);
      glEnable(GL_CULL_FACE);

  #define PROGRAM_VERTEX_ATTRIBUTE 0
  #define PROGRAM_TEXCOORD_ATTRIBUTE 1

      QOpenGLShader *vshader = new QOpenGLShader(QOpenGLShader::Vertex, this);
      const char *vsrc =
          "attribute highp vec4 vertex;\n"
          "attribute mediump vec4 texCoord;\n"
          "varying mediump vec4 texc;\n"
          "uniform mediump mat4 matrix;\n"
          "void main(void)\n"
          "{\n"
          "    gl_Position = matrix * vertex;\n"
          "    texc = texCoord;\n"
          "}\n";
      vshader->compileSourceCode(vsrc);

      QOpenGLShader *fshader = new QOpenGLShader(QOpenGLShader::Fragment, this);
      const char *fsrc =
          "uniform sampler2D texture;\n"
          "varying mediump vec4 texc;\n"
          "void main(void)\n"
          "{\n"
          "    gl_FragColor = texture2D(texture, texc.st);\n"
          "}\n";
      fshader->compileSourceCode(fsrc);

      program = new QOpenGLShaderProgram;
      program->addShader(vshader);
      program->addShader(fshader);
      program->bindAttributeLocation("vertex", PROGRAM_VERTEX_ATTRIBUTE);
      program->bindAttributeLocation("texCoord", PROGRAM_TEXCOORD_ATTRIBUTE);
      program->link();

      program->bind();
      program->setUniformValue("texture", 0);
  }

  void GLWidget::paintGL()
  {
      glClearColor(clearColor.redF(), clearColor.greenF(), clearColor.blueF(), clearColor.alphaF());
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

      QMatrix4x4 m;
      m.ortho(-0.5f, +0.5f, +0.5f, -0.5f, 4.0f, 15.0f);
      m.translate(0.0f, 0.0f, -10.0f);
      m.rotate(xRot / 16.0f, 1.0f, 0.0f, 0.0f);
      m.rotate(yRot / 16.0f, 0.0f, 1.0f, 0.0f);
      m.rotate(zRot / 16.0f, 0.0f, 0.0f, 1.0f);

      program->setUniformValue("matrix", m);
      program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
      program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
      program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
      program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));

      for (int i = 0; i < 6; ++i) {
          textures[i]->bind();
          glDrawArrays(GL_TRIANGLE_FAN, i * 4, 4);
      }
  }
  void GLWidget::resizeGL(int width, int height)
  {
      int side = qMin(width, height);
      glViewport((width - side) / 2, (height - side) / 2, side, side);
  }

  void GLWidget::mousePressEvent(QMouseEvent *event)
  {
      lastPos = event->pos();
  }

  void GLWidget::mouseMoveEvent(QMouseEvent *event)
  {
      int dx = event->x() - lastPos.x();
      int dy = event->y() - lastPos.y();

      if (event->buttons() & Qt::LeftButton) {
          rotateBy(8 * dy, 8 * dx, 0);
      } else if (event->buttons() & Qt::RightButton) {
          rotateBy(8 * dy, 0, 8 * dx);
      }
      lastPos = event->pos();
  }

  void GLWidget::mouseReleaseEvent(QMouseEvent * /* event */)
  {
      emit clicked();
  }

  void GLWidget::makeObject()
  {
      static const int coords[6][4][3] = {
          { { +1, -1, -1 }, { -1, -1, -1 }, { -1, +1, -1 }, { +1, +1, -1 } },
          { { +1, +1, -1 }, { -1, +1, -1 }, { -1, +1, +1 }, { +1, +1, +1 } },
          { { +1, -1, +1 }, { +1, -1, -1 }, { +1, +1, -1 }, { +1, +1, +1 } },
          { { -1, -1, -1 }, { -1, -1, +1 }, { -1, +1, +1 }, { -1, +1, -1 } },
          { { +1, -1, +1 }, { -1, -1, +1 }, { -1, -1, -1 }, { +1, -1, -1 } },
          { { -1, -1, +1 }, { +1, -1, +1 }, { +1, +1, +1 }, { -1, +1, +1 } }
      };

      for (int j = 0; j < 6; ++j)
          textures[j] = new QOpenGLTexture(QImage(QString(":/images/side%1.png").arg(j + 1)).mirrored());

      QVector<GLfloat> vertData;
      for (int i = 0; i < 6; ++i) {
          for (int j = 0; j < 4; ++j) {
              // vertex position
              vertData.append(0.2 * coords[i][j][0]);
              vertData.append(0.2 * coords[i][j][1]);
              vertData.append(0.2 * coords[i][j][2]);
              // texture coordinate
              vertData.append(j == 0 || j == 3);
              vertData.append(j == 0 || j == 1);
          }
      }

      vbo.create();
      vbo.bind();
      vbo.allocate(vertData.constData(), vertData.count() * sizeof(GLfloat));
  }