A proper way to make animation of AIS_Shape on scene

See:
> AIS_Animation wouldn't do everything for you "automatically" - it should be properly initialized (defining animation sequence(s) - key frames)
> and used (to redraw viewer at proper intervals) at application level.

AIS_Animation::StartTimer() starts its internal timer returning elapsed time, the actual update of current frame is done by AIS_Animation::UpdateTimer(), which should be called before redrawing new frame in 3D Viewer.
Redrawing the viewer should be done by application itself, and will depend on used GUI framework and application design.

Thanks for your contribution

thanks very much for your code.
I don't know if I should ask here, 
this code worked correctly 
but I tried to write this code within another "thread"  to get other functionalities in my app, like rotation,
so when I tried that  I had some problems:

1- the Viewer did not update, and I could not see it moving.

2- if I made another process in the main thread, I will get an exception in function "UpdateCurrentViewer"

can you give me some help, please?

bioan wrote:

I like to create a simple animation (have an array of points and want a tool - cylinder - to follow the points array path) and could find any ideas to advance in this problem.

The common solution looks like this:

• Define duration of the whole animation and assign presentation timestamp to each point in array.
  • In the simplest case of equally distributed points this could be just splitting the whole duration by a number of points, or by calculating time based on the distance between points and linear speed.
  • In more complex cases of robotic animation that have other constraints (like maximum linear and angular speeds) the calculation will depend on specific robotics system.
• Define object's (cylinder) location based on your point definition.
  • Considering the point is defined as gp_Ax2/gp_Ax3, you may construct gp_Trsf from these axes taking into account coordinate system, in which object is defined. In the simplest case this looks like this:

    gp_Ax3 theAxes = ...;
    gp_Trsf aTrsf;
    aTrsf.SetTransformation (theAxes, gp::XOY());
    ...
    Handle(AIS_InteractiveContext) theContext = ...;
    Handle(AIS_Shape) theShape = ...;
    theContext->SetLocation (theShape, aTrsf, true);

• Define your own animation object, based on AIS_Animation or AIS_AnimationObject implementing AIS_Animation::update() interface.
  • This method receives a time to be displayed on the screen in form of AIS_AnimationProgress structure.
    Iterate over your point array and find two closest timestamps before and after current time (or equal to current time).
  • Compute an interpolated location (transformation) between these two points.
    gp_TrsfNLerp could be used for that purpose, which performs a per-component linear interpolation (location, orientation).
    You may define your own math that suits better in your case (for instance, you may involve a kinematics solver for this).

    void MyAnimation::update (const AIS_AnimationProgress& theProgress)
    {
      // find closest points
      int aPntIter = 0;
      for (; aPntIter < myNbPoints; ++aPntIter)
      {
        if (myPoints[aPntIter].Timestamp >= theProgress.LocalPts)
        {
          break;
        }
      }
      if (aPntIter == 0 || aPntIter == myNbPoints)
      {
        // clamp to the first / last point position
      }
    
      // take closest locations
      gp_Trsf aTrsfBefore = myPoints[aPntIter - 1].Trsf; // range checks are missing!
      gp_Trsf aTrsfAfter  = myPoints[aPntIter].Trsf;
      gp_TrsfNLerp aTrsfLerp (aTrsfBefore, aTrsfAfter);
    
      // interpolate closest locations
      double aLocalDuration = myPoints[aPntIter].Timestamp - myPoints[aPntIter - 1].Timestamp;
      double aLocalProgress = theProgress.LocalPts - myPoints[aPntIter - 1].Timestamp;
      gp_Trsf aTrsf;
      aTrsfLerp.Interpolate (aLocalProgress / aLocalDuration, aTrsf);
    
      // assign new location to interactive object
      if (!myContext.IsNull())
      {
        myContext->SetLocation (myObject, aTrsf);
        invalidateViewer();
      }
      else
      {
        myObject->SetLocalTransformation (aTrsf);
      }
    }

• Start AIS_Animation playback in some way.
  • If you will assign animation to AIS_ViewController::ObjectsAnimation() property, view controller will allow camera manipulations during object's animation.

1. what kind of data is a presentation timestamp? (never use it before)

Presentation timestamp is a time (in seconds) on animation timeline when specific animation position should be displayed on the screen.

2. how a presentation timestamp could be attached to a gp_Pnt?

It is up to application to define animation timeline.

3. in cases of Mb size of gp_Pnt's, just defining the duration of the whole animation wouldn't be a very consuming process?

You may compute a timestamp for each point on-the-fly in case if animation timeline has a simple curve. I don't see any reason for performance issues to compute timestamps before starting animation, though.

4. why doesn't exist a simple and complete example of basic implementation

There are some legacy animation samples coming with OCCT. Fill free to contribute / share your sample code / article when you will figure out implementation details.

As for reusable mechanism inside OCCT itself - from my point of view different CAD applications compute animation pipeline in very different ways, so that a generalized solution is not applicable or wouldn't suffice different needs. There are also some interfaces defining Kinematics in STEP standard (CAD world), as well as simple animation workflow defined in glTF format (non-CAD world), which could be applicable to some scenarios.

bioan wrote:

I'm asking for a basic approach, without intention of a generalized one. But just to have a starting point, nothing more!

Sure, animation is in my TODO list of articles - along with a dozen of other topics I would like to write about. Animation doesn't look like a simple subject to me, based on my background in writing a video player (where "presentation timestamp" (PTS), "decoding timestamp" (DTS) and other similar terms come from) and implementing animation in a couple of CAD applications. So, indeed, I may overcomplicate things here.

Meanwhile, maybe somebody else from OCCT community would be able to share experience and samples for the topic.

bioan wrote:

So, my question is how to deal with this problem and implement AIS_ViewController::ObjectsAnimation() property.

occt-hello-viewer/aisobject includes a code snippet using AIS_ViewController::ObjectsAnimation(). You may try building this sample and finding some useful hints from there.

  MyViewer()
  {
    ...
    Handle(MyAisObject) aPrs = new MyAisObject();
    aPrs->SetAnimation (AIS_ViewController::ObjectsAnimation());
    ...
  }

...

bool MyAisOwner::HandleMouseClick()
{
  ...
  gp_Trsf aTrsfTo;
  aTrsfTo.SetRotation (gp_Ax1 (gp::Origin(), gp::DX()), isFirst ? M_PI * 0.5 : -M_PI * 0.5);
  gp_Trsf aTrsfFrom = anObj->LocalTransformation();
  Handle(AIS_AnimationObject) anAnim = new AIS_AnimationObject ("MyAnim", anObj->InteractiveContext(), anObj, aTrsfFrom, aTrsfTo);
  anAnim->SetOwnDuration (2.0);

  myAnim->Clear();
  myAnim->Add (anAnim);
  myAnim->StartTimer (0.0, 1.0, true
  ...

bioan wrote

1. can I mix the old V3d_View methods with AIS_ViewController functionality? These two can co-exist inside a single project?

You may call V3d_View methods with a caution, but uncontrolled mixture of AIS_ViewController/V3d_View for camera manipulations (as well as redrawing the View) may lead to unexpected results and visual glitches. AIS_ViewController is not just a tool that helps with camera manipulations, it is also a workflow designed to say when and how to manage viewer events and to avoid unexpected viewer redraws.

2. In the example posted - occt-hello-viewer/aisobject - MyViewer : public AIS_ViewController() is implemented at the very low level of operating system (creating the window, setting the window message handler, etc). Is not the case in my project, everything is just in place,

This particular sample doesn't use any external GUI framework, but you may find other samples demonstrating AIS_ViewController usage with popular GUI frameworks like Qt/QtWidgets, QtQuick/QML, GTK, MFC and some others.

the only need is to unfrozen the display

AIS_ViewController here is just an interface to control mouse input (for camera manipulations), animations (of camera and objects) and viewer updates in a single place and in a well-defined order. You may solve this task at application level by (re)organizing viewer updates and camera manipulations in desired way.

The first step to unblock animation is to call AIS_Animation::UpdateTimer() one time within application-managed callback (using multimedia timers in GUI framework or similar approaches - so that animation updates will be interleaved with user input events) instead of calling it within the fixed loop (in this case user input events will arrive only after for-loop completion).

bioan wrote:

So, to unblock animation there is no need to deal with AIS_ViewController class, just need to be focused of a proper viewer update within app callback events. Correct me if I'm wrong!

This is correct. AIS_Animation class exists since 2016 (OCCT 7.1.0), while AIS_ViewController has been added later in 2019 (OCCT 7.4.0).