Custom elements

Important: this is an experimental feature, please proceed with caution.
We're kindly asking you to report any bugs and suggest following changelog for the most recent updates.

Custom elements allow you to create your own shapes and add them to the canvas.

By design Polotno supports several main types of elements: text, image, svg, line, group. In some cases you may want to create your own custom elements.

Before you start, please note that:

Custom elements are not supported in Cloud Render API.
By default polotno-node (for backend rendering) does not support custom elements. But with some extra configuration you can make it work.
You will need to know some Polotno internals to support animations for custom elements. Please write us if you need need help.
In the future there will be more options for design export (e.g. to SVG, print-ready PDF, etc). You will need to write some adopters to make it work with custom elements.
If possible, try to use built-in elements. For example you can draw some complex shapes using svg element (you can generate src in the runtime).

How to create custom shapes with Polotno?

As the demonstration we will create a custom star element. Creating new elements consists of three main steps.

1. Create model for your element

First define any additional attributes for the new element. All the basic attributes such as id, x, y, rotation, filters attributes, and etc. are defined by default. All that needed is additional data and default values:

import { unstable_registerShapeModel } from 'polotno/config';

unstable_registerShapeModel(
  // define properties
  {
    type: 'star',
    radius: 100,
    fill: 'black',
    numPoints: 6,
  },
  // optional extend function
  (starModel) => {
    // starModel is a model from mobx-state-tree
    // we can define some additional methods here
    // and return it back
    return starModel.actions((self) => {
      return {
        setNumPoints(numPoints) {
          self.numPoints = numPoints;
        },
      };
    });
  }
);

Now polotno store knows that we can define star model.

2. Create react component for new element

Next define how to display the model. To get there, create a react component with react-konva shapes.

// polotno is made with mobx library
// we will need its tools to make reactive components
import { observer } from 'mobx-react-lite';
// import Konva components
import { Star } from 'react-konva';

import { unstable_registerShapeComponent } from 'polotno/config';

// now we need to define how elements looks on canvas
export const StarElement = observer(({ element, store }) => {
  const ref = React.useRef(null);

  const handleChange = (e) => {
    const node = e.currentTarget;
    const scaleX = node.scaleX();
    // Konva.Transformer is changing scale by default
    // we don't need that, so we reset it back to 1.
    node.scaleX(1);
    node.scaleY(1);
    // and then save all changes back to the model
    element.set({
      x: node.x(),
      y: node.y(),
      rotation: e.target.rotation(),
      radius: element.radius * scaleX,
    });
  };

  // VERY IMPORTANT note!
  // element.x and element.y - must define top-left corner of the shape
  // so all position attributes are consistent across all elements
  return (
    <Star
      ref={ref}
      // remember to use "element" name. Polotno will use it internally to find correct node
      name="element"
      // also it is important to pass id
      // so polotno can automatically do selection
      id={element.id}
      x={element.x}
      y={element.y}
      fill={element.fill}
      offsetX={-element.radius}
      offsetY={-element.radius}
      rotation={element.rotation}
      opacity={element.opacity}
      draggable={!element.locked}
      outerRadius={element.radius}
      innerRadius={element.radius * 0.5}
      onDragMove={handleChange}
      onTransform={handleChange}
    />
  );
});

// now we can register new component to draw our star
unstable_registerShapeComponent('star', StarElement);

3. Create custom top toolbar (optional)

A custom toolbar can be defined to change star properties.

import React from 'react';
import { observer } from 'mobx-react-lite';
import { NumericInput, Navbar, Alignment } from '@blueprintjs/core';

import ColorPicker from 'polotno/toolbar/color-picker';
import { unstable_registerToolbarComponent } from 'polotno/config';

const StarToolbar = observer(({ store }) => {
  const element = store.selectedElements[0];

  return (
    <Navbar.Group align={Alignment.LEFT}>
      <ColorPicker
        value={element.fill}
        onChange={(fill) =>
          element.set({
            fill,
          })
        }
        store={store}
      />
      <NumericInput
        onValueChange={(radius) => {
          element.set({ height: radius });
        }}
        value={element.radius}
        style={{ width: '50px', marginLeft: '10px' }}
        min={1}
        max={40}
      />
    </Navbar.Group>
  );
});

unstable_registerToolbarComponent('star', StarToolbar);