Creating Tools

Note

If your method of adding tools is to fork the project or edit the generated JS, please don’t. If you need custom tools for your particular application, you can do that without changing Literally Canvas’s source code. That is the entire purpose of this API.

If you want to contribute a tool to the project, then by all means, clone the repository and send us a pull request.

Literally Canvas has two APIs for creating tools: a simple API (old style) and a normal API (new style).

For both APIs, a tool is an object with a specific set of keys.

name
Unique identifier for the tool.
iconName
Name of the image to be used in the toolbar for this tool, not including the extension. The full URL of the image will be {imageURLPrefix}/{iconName}.png.
optionsStyle

Which toolbar to show while this tool is active. There is a crappy API available to add new possibilities. The built-in values are:

null or 'null'
Show nothing.
'stroke-width'
Show a stroke width picker and set the tool’s strokeWidth property.
'font'
Set the tool’s font property to a canvas-compatible font string.
var MyTool = function(lc) {  // take lc as constructor arg
  var self = this;

  return {
    name: 'MyTool',
    iconName: 'line',

    optionsStyle: 'stroke-width',
    strokeWidth: lc.opts.defaultStrokeWidth,
    // ...more to follow
  }
};

LC.init(el, {
  // Add me to the toolbar
  tools: LC.defaultTools.concat([MyTool])
});

Simple API

To implement a tool using the “simple” API, you just need to implement three lifecycle methods: begin, continue, and end.

Here’s an alternate version of the line tool.

Note

This code block hasn’t been tested, so you might have to file a bug report and get it fixed.

var MyTool = function(lc) {  // take lc as constructor arg
  var self = this;

  return {
    name: 'MyTool',
    iconName: 'line',
    strokeWidth: lc.opts.defaultStrokeWidth,
    optionsStyle: 'stroke-width',

    begin: function(x, y, lc) {
      self.currentShape = LC.createShape('Line', {
        x1: x, y1: y, x2: x, y2: y,
        self.strokeWidth, color: lc.getColor('primary')});
    },

    continue: function(x, y, lc) {
      self.currentShape.x2 = x;
      self.currentShape.y2 = y;
      lc.setShapesInProgress([self.currentShape]);
    },

    end: function(x, y, lc) {
      self.currentShape.x2 = x;
      self.currentShape.y2 = y;
      lc.setShapesInProgress([]);
      lc.saveShape(self.currentShape);
    }
  }
};

LC.init(el, {
  // Add me to the toolbar
  tools: LC.defaultTools.concat([MyTool])
});

Normal API

If you want more sophisticated behavior than just touch-drag-release, you can attach event handlers and listen to pointer events and do anything you like.

Here’s the same tool implemented using the normal API.

var MyTool = function(lc) {  // take lc as constructor arg
  var self = this;

  return {
    usesSimpleAPI: false,  // DO NOT FORGET THIS!!!
    name: 'MyTool',
    iconName: 'line',
    strokeWidth: lc.opts.defaultStrokeWidth,
    optionsStyle: 'stroke-width',

    didBecomeActive: function(lc) {
      var onPointerDown = function(pt) {
        self.currentShape = LC.createShape('Line', {
          x1: pt.x, y1: pt.y, x2: pt.x, y2: pt.y,
          self.strokeWidth, color: lc.getColor('primary')});
        lc.setShapesInProgress([self.currentShape]);
        lc.repaintLayer('main');
      };

      var onPointerDrag = function(pt) {
        self.currentShape.x2 = pt.x;
        self.currentShape.y2 = pt.y;
        lc.setShapesInProgress([self.currentShape]);
        lc.repaintLayer('main');
      };

      var onPointerUp = function(pt) {
        self.currentShape.x2 = pt.x;
        self.currentShape.y2 = pt.y;
        lc.setShapesInProgress([]);
        lc.saveShape(self.currentShape);
      };

      var onPointerMove = function(pt) {
        console.log("Mouse moved to", pt);
      };

      // lc.on() returns a function that unsubscribes us. capture it.
      self.unsubscribeFuncs = [
        lc.on('lc-pointerdown', onPointerDown),
        lc.on('lc-pointerdrag', onPointerDrag),
        lc.on('lc-pointerup', onPointerUp),
        lc.on('lc-pointermove', onPointerMove)
      ];
    },

    willBecomeInactive: function(lc) {
      // call all the unsubscribe functions
      self.unsubscribeFuncs.map(function(f) { f() });
    }
  }
};

LC.init(el, {
  // Add me to the toolbar
  tools: LC.defaultTools.concat([MyTool])
});

Tools can call any method on the given LiterallyCanvas() object. Usually you’ll be drawing and adding shapes, but you can also set colors, pan, zoom, trigger events, and more. If you’re feeling adventurous, you can add new DOM nodes to lc.containerEl with on-screen UI, like the text and polygon tools do. Just make sure you clean up when your tool is deactivated!

There may eventually be a better API for adding UI to tools.

Options styles

Note

This is the roughest edge of the extensibility API. You may need to make minor changes to your custom tools in the future when we improve it.

When you activate a tool, the bottom toolbar changes to show the tool’s current state. The two built-in options styles are 'stroke-width' and font.

The stroke-width style will “magically” set tool.strokeWidth on the active tool when the user clicks an option.

The font style will set tool.text to the user-entered text, and tool.font to a canvas-compatible font string like italic 18px Garamond.

To define your own options style, use this function:

LC.defineOptionsStyle(identifier, ReactComponent)
Arguments:
  • identifier – String used as the value of tool.optionsStyle to attach this options style to that tool.
  • ReactComponent – A React component taking the props lc and tool. lc is the LiterallyCanvas() instance, and tool is the tool instance. This component will be inserted into the bottom toolbar.

For examples, read the source files src/optionsStyles/stroke-width.coffee and src/optionsStyles/font.coffee. If you need additional assistance, and already understand React.js, please ask the mailing list for help. Our response time is great.

You should open GitHub issues if you would like specific UI or code improvements to the existing options styles, or if you think a new kind of generalized option style would helpful.

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