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add docs about onGazeUpdate

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Josh de Leeuw 2021-03-15 10:40:59 -04:00
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docs/extensions/jspsych-ext-webgazer.md
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@ -109,11 +109,20 @@ The extension uses the default mode specified by WebGazer (currently `ridge`).
### getCurrentPrediction() ### getCurrentPrediction()
Get the current predicted gaze location from WebGazer. Returns an object with `x`, `y`, and `eyeFeature` properties. This function is asynchronus, so proper use requires either the `await` keyword in the context of another `async function` or using `.then()`. Get the current predicted gaze location from WebGazer. Returns an object with `x`, `y`, and, if currently in a trial with the extension turned on, the time `t` in ms since the start of the trial.
### onGazeUpdate(callback)
Subscribe to gaze updates. The `callback` will be invoked every time a new gaze prediction is generated. The first argument of the `callback` will be an object with `x`, `y`, and, if currently in a trial with the extension turned on, the time `t` in ms since the start of the trial.
This function returns a close handler. When you no longer need to subscribe to gaze updates, call the close handler. Example:
```js ```js
jsPsych.extensions.webgazer.getCurrentPrediction().then(function(data){ var cancelGazeUpdateHandler = jsPsych.extensions.webgazer.onGazeUpdate(function(prediction){
console.log(`Currently looking at coordinate ${data.x}, ${data.y}`) console.log(`Currently looking at ${prediction.x}, ${prediction.y}`);
}); });
cancelGazeUpdateHandler();
``` ```
You can add multiple handlers. Handlers are not closed automatically, so be sure to cancel them when no longer needed.