Generating events for gesture-controlled websites

问题:

I am very happy that I got the opportunity to work on a website that is gesture-based. I have a few inspiration for this: link

I visited lot of websites and googled it, Wikipedia and gitHub also didn't help much. There is not much information provided as these technologies are in nascent stages. I think I will have to use some js for this project

1. gesture.js (our custom javascript code)
2. reveal.js (Frame work for slideshow)

My questions are how come gestures generate events, how does my JavaScript interact with my webcam? Do I have to use some API or algorithms?

I am not asking for code. I am just asking the mechanism, or some links providing vital info will do. I seriously believe that if the accuracy on this technology can be improved, this technology can do wonders in the near future.

回答1:

To enable gestural interactions in a web app, you can use navigator.getUserMedia() to get video from your local webcam, periodically put video frame data into a canvas element and then analyse changes between frames.

There are several JavaScript gesture libraries and demos available (including a nice slide controller). For face/head tracking you can use libraries like headtrackr.js: example at simpl.info/headtrackr.

回答2:

I'm playing a little bit with that at the moment so, from what I understood the most basic technique is:

1. you request to use the user's webcam to take a video.
2. when permission is given, create a canvas in which to put the video.
3. you use a filter (black and white) on the video.
4. you put some control points in the canvas frame (a small area in where all the pixel colors in it are registered)
5. you start attaching a function for each frame (for the purpose of the explanation, I'll only demonstrate left-right gestures)

At each frame:

• If the frame is the first (F0) continue
• If not: we subtract the current frame's pixels (Fn) from the previous one
  • if there were no movement between Fn and F(n-1) all the pixels will be black
  • if there are, you will see the difference Delta = Fn - F(n-1) as white pixels
• Then you can test your control points for which areas are light up and store them ( ** )x = DeltaN

Repeat the same operations until you have two or more Deltas variables and you subtract the control points DeltaN from the control points Delta(n-1) and you'll have a vector

• ( **)x = DeltaN
• ( ** )x = Delta(N-1)
• ( +2 )x = DeltaN - Delta(N-1)

You can now test if the vector is either positive or negative, or test if the values are superior to some value of your choosing

if positive on x and value > 5

and trigger an event, then listen to it:

$(document).trigger('MyPlugin/MoveLeft', values)
$(document).on('MyPlugin/MoveLeft', doSomething)

You can greatly improve the precision by caching the vectors or adding them and only trigger an event when the vector values becomes a sensible value.

You can also expect a shape on your first subtractions and try to map a "hand" or a "box" and listen to the changes of the shape's coordinates, but remember the gestures are in 3D and the analysis is 2D so the same shape can change while moving.

Here's a more precise explanation. Hope my explanation helped.