glwidget.cpp Example File

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  #include "glwidget.h"
  #include <QMouseEvent>
  #include <QOpenGLShaderProgram>
  #include <QCoreApplication>
  #include <math.h>

  GLWidget::GLWidget(QWidget *parent)
      : QOpenGLWidget(parent),
        m_xRot(0),
        m_yRot(0),
        m_zRot(0),
        m_program(0)
  {
      m_core = QCoreApplication::arguments().contains(QStringLiteral("--coreprofile"));
      // --transparent causes the clear color to be transparent. Therefore, on systems that
      // support it, the widget will become transparent apart from the logo.
      m_transparent = QCoreApplication::arguments().contains(QStringLiteral("--transparent"));
      if (m_transparent) {
          QSurfaceFormat fmt = format();
          fmt.setAlphaBufferSize(8);
          setFormat(fmt);
      }
  }

  GLWidget::~GLWidget()
  {
      cleanup();
  }

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

  QSize GLWidget::sizeHint() const
  {
      return QSize(400, 400);
  }

  static void qNormalizeAngle(int &angle)
  {
      while (angle < 0)
          angle += 360 * 16;
      while (angle > 360 * 16)
          angle -= 360 * 16;
  }

  void GLWidget::setXRotation(int angle)
  {
      qNormalizeAngle(angle);
      if (angle != m_xRot) {
          m_xRot = angle;
          emit xRotationChanged(angle);
          update();
      }
  }

  void GLWidget::setYRotation(int angle)
  {
      qNormalizeAngle(angle);
      if (angle != m_yRot) {
          m_yRot = angle;
          emit yRotationChanged(angle);
          update();
      }
  }

  void GLWidget::setZRotation(int angle)
  {
      qNormalizeAngle(angle);
      if (angle != m_zRot) {
          m_zRot = angle;
          emit zRotationChanged(angle);
          update();
      }
  }

  void GLWidget::cleanup()
  {
      makeCurrent();
      m_logoVbo.destroy();
      delete m_program;
      m_program = 0;
      doneCurrent();
  }

  static const char *vertexShaderSourceCore =
      "#version 150\n"
      "in vec4 vertex;\n"
      "in vec3 normal;\n"
      "out vec3 vert;\n"
      "out vec3 vertNormal;\n"
      "uniform mat4 projMatrix;\n"
      "uniform mat4 mvMatrix;\n"
      "uniform mat3 normalMatrix;\n"
      "void main() {\n"
      "   vert = vertex.xyz;\n"
      "   vertNormal = normalMatrix * normal;\n"
      "   gl_Position = projMatrix * mvMatrix * vertex;\n"
      "}\n";

  static const char *fragmentShaderSourceCore =
      "#version 150\n"
      "in highp vec3 vert;\n"
      "in highp vec3 vertNormal;\n"
      "out highp vec4 fragColor;\n"
      "uniform highp vec3 lightPos;\n"
      "void main() {\n"
      "   highp vec3 L = normalize(lightPos - vert);\n"
      "   highp float NL = max(dot(normalize(vertNormal), L), 0.0);\n"
      "   highp vec3 color = vec3(0.39, 1.0, 0.0);\n"
      "   highp vec3 col = clamp(color * 0.2 + color * 0.8 * NL, 0.0, 1.0);\n"
      "   fragColor = vec4(col, 1.0);\n"
      "}\n";

  static const char *vertexShaderSource =
      "attribute vec4 vertex;\n"
      "attribute vec3 normal;\n"
      "varying vec3 vert;\n"
      "varying vec3 vertNormal;\n"
      "uniform mat4 projMatrix;\n"
      "uniform mat4 mvMatrix;\n"
      "uniform mat3 normalMatrix;\n"
      "void main() {\n"
      "   vert = vertex.xyz;\n"
      "   vertNormal = normalMatrix * normal;\n"
      "   gl_Position = projMatrix * mvMatrix * vertex;\n"
      "}\n";

  static const char *fragmentShaderSource =
      "varying highp vec3 vert;\n"
      "varying highp vec3 vertNormal;\n"
      "uniform highp vec3 lightPos;\n"
      "void main() {\n"
      "   highp vec3 L = normalize(lightPos - vert);\n"
      "   highp float NL = max(dot(normalize(vertNormal), L), 0.0);\n"
      "   highp vec3 color = vec3(0.39, 1.0, 0.0);\n"
      "   highp vec3 col = clamp(color * 0.2 + color * 0.8 * NL, 0.0, 1.0);\n"
      "   gl_FragColor = vec4(col, 1.0);\n"
      "}\n";

  void GLWidget::initializeGL()
  {
      // In this example the widget's corresponding top-level window can change
      // several times during the widget's lifetime. Whenever this happens, the
      // QOpenGLWidget's associated context is destroyed and a new one is created.
      // Therefore we have to be prepared to clean up the resources on the
      // aboutToBeDestroyed() signal, instead of the destructor. The emission of
      // the signal will be followed by an invocation of initializeGL() where we
      // can recreate all resources.
      connect(context(), &QOpenGLContext::aboutToBeDestroyed, this, &GLWidget::cleanup);

      initializeOpenGLFunctions();
      glClearColor(0, 0, 0, m_transparent ? 0 : 1);

      m_program = new QOpenGLShaderProgram;
      m_program->addShaderFromSourceCode(QOpenGLShader::Vertex, m_core ? vertexShaderSourceCore : vertexShaderSource);
      m_program->addShaderFromSourceCode(QOpenGLShader::Fragment, m_core ? fragmentShaderSourceCore : fragmentShaderSource);
      m_program->bindAttributeLocation("vertex", 0);
      m_program->bindAttributeLocation("normal", 1);
      m_program->link();

      m_program->bind();
      m_projMatrixLoc = m_program->uniformLocation("projMatrix");
      m_mvMatrixLoc = m_program->uniformLocation("mvMatrix");
      m_normalMatrixLoc = m_program->uniformLocation("normalMatrix");
      m_lightPosLoc = m_program->uniformLocation("lightPos");

      // Create a vertex array object. In OpenGL ES 2.0 and OpenGL 2.x
      // implementations this is optional and support may not be present
      // at all. Nonetheless the below code works in all cases and makes
      // sure there is a VAO when one is needed.
      m_vao.create();
      QOpenGLVertexArrayObject::Binder vaoBinder(&m_vao);

      // Setup our vertex buffer object.
      m_logoVbo.create();
      m_logoVbo.bind();
      m_logoVbo.allocate(m_logo.constData(), m_logo.count() * sizeof(GLfloat));

      // Store the vertex attribute bindings for the program.
      setupVertexAttribs();

      // Our camera never changes in this example.
      m_camera.setToIdentity();
      m_camera.translate(0, 0, -1);

      // Light position is fixed.
      m_program->setUniformValue(m_lightPosLoc, QVector3D(0, 0, 70));

      m_program->release();
  }

  void GLWidget::setupVertexAttribs()
  {
      m_logoVbo.bind();
      QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();
      f->glEnableVertexAttribArray(0);
      f->glEnableVertexAttribArray(1);
      f->glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), 0);
      f->glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), reinterpret_cast<void *>(3 * sizeof(GLfloat)));
      m_logoVbo.release();
  }

  void GLWidget::paintGL()
  {
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
      glEnable(GL_DEPTH_TEST);
      glEnable(GL_CULL_FACE);

      m_world.setToIdentity();
      m_world.rotate(180.0f - (m_xRot / 16.0f), 1, 0, 0);
      m_world.rotate(m_yRot / 16.0f, 0, 1, 0);
      m_world.rotate(m_zRot / 16.0f, 0, 0, 1);

      QOpenGLVertexArrayObject::Binder vaoBinder(&m_vao);
      m_program->bind();
      m_program->setUniformValue(m_projMatrixLoc, m_proj);
      m_program->setUniformValue(m_mvMatrixLoc, m_camera * m_world);
      QMatrix3x3 normalMatrix = m_world.normalMatrix();
      m_program->setUniformValue(m_normalMatrixLoc, normalMatrix);

      glDrawArrays(GL_TRIANGLES, 0, m_logo.vertexCount());

      m_program->release();
  }

  void GLWidget::resizeGL(int w, int h)
  {
      m_proj.setToIdentity();
      m_proj.perspective(45.0f, GLfloat(w) / h, 0.01f, 100.0f);
  }

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

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

      if (event->buttons() & Qt::LeftButton) {
          setXRotation(m_xRot + 8 * dy);
          setYRotation(m_yRot + 8 * dx);
      } else if (event->buttons() & Qt::RightButton) {
          setXRotation(m_xRot + 8 * dy);
          setZRotation(m_zRot + 8 * dx);
      }
      m_lastPos = event->pos();
  }