Wednesday, February 4, 2015

Unity 4.6: Silent conversation - Detecting head gestures for yes and no

One of the demos that I have really enjoyed is the “Trial of the Rift Drifter” by Aldin Dynamics. In this demo you answer questions by shaking your head for yes and no. This is a great use of the head tracker data beyond changing the user’s point of view. And it is a mechanic that I would like to add to my own applications as it really adds to the immersive feel.

As an example, I updated the thought bubbles scene I created earlier to allow a silent conversation with one of the people in the scene and this blog post will cover exactly what I did.

In my scene, I used a world-space canvas to create the thought bubble. This canvas contains a canvas group (ThoughtBubble) which contains an image UI object and a text UI object.

Hierarchy of the world space canvas  
I wanted the text in this canvas to change in response to the user shaking their head yes or no. I looked at a couple of different ways of detecting nods and head shakes, but ultimately went with a solution based on this project by Katsuomi Kobayashi.

To use the gesture recognition solution from this project in my own project, I first added the two Rift Gesture files (RiftGesture.cs and MyMath.cs) to my project and then attached the RiftGesture.cs script to the ThoughtBubble.

When you look at RiftGesture.cs, there are two things to take note of. First, you’ll see that to get the head orientation data, it uses:

OVRPose pose = OVRManager.display.GetHeadPose();
Quaternion q = pose.orientation;

This gets the head pose data from the Rift independent of any other input. When I first looked at adding head gestures, I tried using the transform from one of the cameras on the logic that the camera transform follows the head pose. Using the camera transform turned out to be problematic because the transform can also be affected by input from devices other than the head set (keyboard, mouse, gamepad) resulting in detecting a headshake when the user rotated the avatar using the mouse rather than shaking their head. By using OVRManager.display.GetHeadPose(), it ensures you are only evaluating data from the headset itself.

Second, you will also notice that it uses SendMessage in DetectNod() when a nod has been detected:

SendMessage("TriggerYes", SendMessageOptions.DontRequireReceiver);

and in DetectHeadshake() when a headshake has been detected:

SendMessage("TriggerNo", SendMessageOptions.DontRequireReceiver);

The next step I took was to create a new script (conversation.cs) to handle the conversation. This script contains a bit of setup to get and update the text in the canvas and to make sure that the dialog is visible to the user before it changes. (The canvas groups visibility is set by canvas groups alpha property.) However, most importantly, this script contains the TriggerYes() and TriggerNo() functions that receive the messages sent from the RiftGesture.cs. These functions simply update the text when a nod or headshake message has been received. I attached the conversation.cs script to the ThoughtBubble object and dragged the text object from the canvas to the questionholder so that the script would know which text to update.

Scripts attached to the ThoughtBubble canvas group

At this point I was able to build and test my scene and have a quick telepathic conversation with one of the characters.

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