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This example is part of our :notebook: custom elements guide. Checkout the final result here.
bpmn-js Example: Custom Rendering
An example of creating custom rendering for bpmn-js. Custom rendering allows you to render any shape or connection the way you want.
About
This example renders bpmn:Task
and bpmn:Event
elements differently.
Creating a Custom Renderer
In order to render bpmn:Task
and bpmn:Event
elements differently we'll create a custom renderer. By extending BaseRenderer we make sure our renderer will be called whenever a shape or connection is to be rendered. Note that we also specify a priority higher than the default priority of 1000 so our renderer will be called first.
const HIGH_PRIORITY = 1500;
export default class CustomRenderer extends BaseRenderer {
constructor(eventBus) {
super(eventBus, HIGH_PRIORITY);
...
}
...
}
Whenever our renderer is called we need to decide whether we want to render an element or if the default renderer should render it. We're only interested in rendering bpmn:Task
and bpmn:Event
elements:
canRender(element) {
// only render tasks and events (ignore labels)
return isAny(element, [ 'bpmn:Task', 'bpmn:Event' ]) && !element.labelTarget;
}
Once we've decided to render an element depending on the element's type our renderers drawShape
or drawConnection
will be called. Since we only render shapes, we don't need to implement drawConnection
. We don't want to render tasks and events entirely different, so we'll let the default renderer do the heavy lifting of rendering the shape and then change it afterward:
drawShape(parentNode, element) {
const shape = this.bpmnRenderer.drawShape(parentNode, element);
if (is(element, 'bpmn:Task')) {
const rect = drawRect(parentNode, 100, 80, TASK_BORDER_RADIUS, '#52B415');
prependTo(rect, parentNode);
svgRemove(shape);
return shape;
}
const rect = drawRect(parentNode, 30, 20, TASK_BORDER_RADIUS, '#cc0000');
svgAttr(rect, {
transform: 'translate(-20, -10)'
});
return shape;
}
If the element is a bpmn:Task
we render the task first and then replace its rectangle with our own rectangle. Therefore, we don't have to render labels and markers ourselves.
In the case of bpmn:Event
elements we let the default renderer render the element first before we render an additional rectangle on top of it.
You can also decide to take care of the rendering entirely on your own without using the default renderer at all.
Finally, since we are rendering shapes we need to implement a getShapePath
method which will be called whenever a connection is to be cropped:
getShapePath(shape) {
if (is(shape, 'bpmn:Task')) {
return getRoundRectPath(shape, TASK_BORDER_RADIUS);
}
return this.bpmnRenderer.getShapePath(shape);
}
See the entire renderer here.
Next, let's add our custom renderer to bpmn-js.
Adding the Custom Renderer to bpmn-js
When creating a new instance of bpmn-js we need to add our custom renderer using the additionalModules
property:
import BpmnModeler from 'bpmn-js/lib/Modeler';
import customRendererModule from './custom';
const bpmnModeler = new BpmnModeler({
additionalModules: [
customRendererModule
]
});
Our custom renderer will now render all task and event shapes.
Run the Example
You need a NodeJS development stack with npm installed to build the project.
To install all project dependencies execute
npm install
To start the example execute
npm start
To build the example into the public
folder execute
npm run all
License
MIT