sketchpad plugin

This plugin creates an interactive canvas that the participant can draw on using their mouse or touchscreen. It can be used for sketching tasks, like asking the participant to draw a particular object. It can also be used for some image segmentation or annotation tasks by setting the background_image parameter to render an image on the canvas.

The plugin stores a base 64 data URL representation of the final image. This can be converted to an image file using online tools or short programs in R, python, or another language of your choice. It also records all of the individual strokes that the participant made during the trial.

Warning

This plugin generates a lot of data. Each trial can easily add 500kb+ of data to a final JSON output. You can reduce the amount of data generated by turning off storage of the individual stroke data (save_strokes: false) or storage of the final image (save_final_image: false) if your use case doesn't require that information. If you are going to be collecting a lot of data with this plugin you may want to save your data to your server after each trial and not wait until the end of the experiment to perform a single bulk upload. You can do this by putting data saving code inside the on_data_update event handler.

Parameters

In addition to the parameters available in all plugins, this plugin accepts the following parameters.

Parameter	Type	Default Value	Description
canvas_shape	"rectangle" or "circle"	"rectangle"	The shape of the canvas element.
canvas_width	int	500	Width of the canvas in pixels when canvas_shape is "rectangle"
canvas_height	int	500	Height of the canvas in pixels when canvas_shape is "rectangle"
canvas_diameter	int	500	Diameter of the canvas in pixels when canvas_shape is "circle"
canvas_border_width	int	0	Width of the canvas border
canvas_border_color	string	"#000"	Color of the canvas border
background_image	image path	null	Path to an image to render as the background of the canvas
background_color	string	"#fff"	Color of the canvas background. Note that a background_image will render on top of the color.
stroke_width	int	2	Width of the stroke on the canvas
stroke_color	string	"#000"	Color of the stroke on the canvas
stroke_color_palette	array of strings	[]	Array of colors to render as a palette of choices for stroke color. Clicking on the corresponding color button will change the stroke color.
prompt	string	null	HTML content to render on the screen.
prompt_location	"abovecanvas" or "belowcanvas" or "belowbutton"	"abovecanvas"	The location to render the prompt content.
save_final_image	bool	true	Whether to save the final image in the data as a base64 encoded data URL.
save_strokes	bool	true	Whether to save the individual stroke data that generated the final image.
key_to_draw	key string	null	If this key is held down then it is like the mouse button being held down. The "ink" will flow when the button is held and stop when it is lifted. Pass in the string representation of the key, e.g., 'a' for the A key or ' ' for the spacebar.
show_finished_button	bool	true	Whether to show the button that ends the trial.
finished_button_label	string	"Finished"	The label for the button that ends the trial.
show_clear_button	bool	true	Whether to show the button that clears the entire drawing.
clear_button_label	string	"Clear"	The label for the button that clears the entire drawing.
show_undo_button	bool	true	Whether to show the button that enables an undo action.
undo_button_label	string	"Undo"	The label for the button that enables an undo action.
show_redo_button	bool	true	Whether to show the button that enables a redo action. Note that show_undo_button must be true for the redo button to show up.
redo_button_label	string	"Redo"	The label for the button that enables a redo action.
choices	array of keys	"NO_KEYS"	This array contains the key(s) that the subject is allowed to press in order to end the trial. Keys should be specified as characters (e.g., 'a', 'q', ' ', 'Enter', 'ArrowDown') - see this page and this page (event.key column) for more examples. Any key presses that are not listed in the array will be ignored. The default value of "NO_KEYS" means that no keys will be accepted as valid responses. Specifying "ALL_KEYS" will mean that all responses are allowed.
trial_duration	int	null	Length of time before the trial ends. If null the trial will continue indefinitely (until another way of ending the trial occurs).
show_countdown_trial_duration	bool	false	Whether to show a timer that counts down until the end of the trial when trial_duration is not null.
countdown_timer_html	string	'<span id="sketchpad-timer"></span> remaining'	The HTML to use for rendering the countdown timer. The element with id="sketchpad-timer" will have its content replaced by a countdown timer in the format MM:SS.

Data Generated

In addition to the default data collected by all plugins, this plugin collects the following data for each trial.

Name	Type	Value
rt	int	The length of time from the start of the trial to the end of the trial.
response	string	If the trial was ended by clicking the finished button, then "button". If the trial was ended by pressing a key, then the key that was pressed. If the trial timed out, then null.
png	base64 data URL string	If save_image is true, then this will contain the base64 encoded data URL for the image, in png format.
strokes	array of stroke objects	If save_strokes is true, then this will contain an array of stroke objects. Objects have an action property that is either "start", "move", or "end". If action is "start" or "move" it will have an x and y property that report the coordinates of the action relative to the upper-left corner of the canvas. If action is "start" then the object will also have a t and color property, specifying the time of the action relative to the onset of the trial (ms) and the color of the stroke. If action is "end" then it will only have a t property.

Simulation Mode

This plugin does not yet support simulation mode.

Examples

Basic sketchpad with a prompt

Code

var trial = {
  type: jsPsychSketchpad,
  prompt: '<p>Draw an apple!</p>',
  prompt_location: 'abovecanvas',
  canvas_width: 300,
  canvas_height: 300,
  canvas_border_width: 2
}

Demo

Open demo in new tab

Image segmentation with different colors

Code

var trial = {
  type: jsPsychSketchpad,
  prompt: '<p style="width:380px">Circle the mouth using red. Circle the eyes using blue.</p>',
  prompt_location: 'abovecanvas',
  stroke_color_palette: ['red', 'blue'],
  stroke_color: 'red',
  background_image: 'img/sad_face_4.jpg',
  canvas_width: 380,
  canvas_height: 252
}

Demo

Open demo in new tab

Draw an image in a time limit, then display the image and ask for a label.

Code

var draw = {
  type: jsPsychSketchpad,
  prompt: '<p>Draw the first animal that comes to mind. You have 30 seconds!</p>',
  prompt_location: 'belowcanvas',
  trial_duration: 30000,
  show_countdown_trial_duration: true,
}

var label = {
  type: jsPsychSurveyText,
  preamble: () => {
    var imageData = jsPsych.data.get().last(1).values()[0].png;
    return `<img src="${imageData}"></img>`;
  },
  questions: [
    {prompt: 'What animal did you draw?'}
  ]
}

Demo

Open demo in new tab