In this topic we'll be looking at is how to move an object in OpenGL using keyboard controls. Qt provides an easy way to detect keyboard events using virtual functions, namely keyPressEvent() and keyReleaseEvent(). We will be using the previous example and adding to it.
- Open up
mainwindow.hand declare two floating point numbers calledmoveXandmoveZ:private: QOpenGLContext* context; QOpenGLFunctions* openGLFunctions; float rotation; GLuint texID[1]; float moveX; float moveZ;
- After that, declare the
keyPressEvent()function, like so:public: explicit MainWindow(QWidget *parent = 0); ~MainWindow(); void keyPressEvent(QKeyEvent *event); - Then, open up
mainwindow.cppand set the default values for the two variables we just declared:MainWindow::MainWindow(QWidget *parent) { setSurfaceType(QWindow::OpenGLSurface); QSurfaceFormat format; format.setProfile(QSurfaceFormat::CompatibilityProfile); format.setVersion(2, 1); // OpenGL 2.1 setFormat(format); context = new QOpenGLContext; context->setFormat(format); context->create(); context->makeCurrent(this); openGLFunctions = context->functions(); QTimer *timer = new QTimer(this); connect(timer, SIGNAL(timeout()), this, SLOT(updateAnimation())); timer->start(100); rotation = 0; moveX = 0; moveZ = 0; } - Next, we will implement the
keyPressEvent()function:void MainWindow::keyPressEvent(QKeyEvent *event) { if (event->key() == Qt::Key_W) { moveZ -= 0.2; } if (event->key() == Qt::Key_S) { moveZ += 0.2; } if (event->key() == Qt::Key_A) { moveX -= 0.2; } if (event->key() == Qt::Key_D) { moveX += 0.2; } } - After that, we call
glTranslatef()before drawing the 3D cube and putting bothmoveXandmoveZinto the function. Also, we disabled the rotation so that it's easier to see the movement:// Transformations glTranslatef(0.0, 0.0, -3.0); glRotatef(rotation, 1.0, 1.0, 1.0); glTranslatef(moveX, 0.0, moveZ); // Texture mapping glEnable(GL_TEXTURE_2D); glBindTexture(GL_TEXTURE_2D, texID[0]); glEnable(GL_LIGHTING);
- If you compile and run the program now, you should be able to move the cube around by pressing W, A, S and D:
Basically, what we did here was add or subtract the moveX and moveZ values when a key is pressed. In keyPressEvent(), we checked whether the keyboard button pressed was W, A, S, or D. Then, we add or subtract 0.2 from the variables accordingly. To get the full list of key names used by Qt, visit http://doc.qt.io/qt-5/qt.html#Key-enum.
When we hold down the same key and don't release it, Qt will repeat the key press event after an interval. The keyboard input interval varies between different operating systems. You can set the interval by calling QApplication::setKeyboardInterval(), but this may not work in every operating system. We called glTranslatef(moveX, 0.0, moveZ) before drawing the cube, which moves the cube around when we press W, A, S, or D.