Using a Camera

In the previous chapter we used the Viewport element to render a scene with a model placed at the origin. When you look at this 3D scene rendered on your monitor, you still see a 2D picture. Quite some computing is required for this. It is done by OpenGL. A mapping of a 3D scene geometry onto a 2D area on your computer monitor (this area is also called the viewport) requires a transformation matrix. This matrix consists of a camera position, a type of projection and a viewing vector. The OpenGL term for this matrix is modelview-projection matrix. Please have a look at the OpenGL Tutorial [http://qt-project.org/wiki/Developer-Guides/] for more details.

Qt3D offers a very convenient way to deal with projections as described above, the Camera [http://qt-project.org/doc/qt-5.0/qml-camera.html] element. The Camera element has the properties to define position, projection type, near and far planes. These properties are used as parameters to calculate according modelview-projection matrix and and projection itself.

Animating the Camera’s position

In the next example, we want to use the camera to rotate around our model, which has been placed at the origin.

The only thing we have to do for this is creating a new Camera element and assign it to the camera property of the Viewport [http://qt-project.org/doc/qt-5.0/qml-viewport.html]. The eye property is the position of the camera and the center is basically the point in the 3D space at which the camera is looking. The default value is the origin so the property would be dispensable in this example:

//game.qml
...
Viewport {
...
  //The game camera
  camera: Camera {
        id: cam
      property real angle:0
        center: Qt.vector3d(0,0,0)
      eye: Qt.vector3d(20    Math.sin(angle), 10, 20*Math.cos(angle))
      NumberAnimation on angle{
          to: 100
          duration: 1000000
      }
  }
...
}

The rotation around the origin has been created in this example by using the sine and cosine together with a NumberAnimation on a custom property called angle. The angle is increasing from 0 to 100 over a big enough timespan.

What’s Next?

Next we will see how to use a Skybox in order to visualize stars in space.