Overcoming SVG Rendering Challenges in React-Konva

In my recent journey working with React-Konva, I tackled the challenge of loading and rendering SVG images within a canvas-based application. While the task seemed straightforward initially, it led me through a deeper understanding of how to handle drag-and-drop interactions, manage image sources in Redux, and dynamically render images on the canvas. Here’s how I approached it and the solution I eventually arrived at.

Problem Overview

I wanted to implement drag-and-drop functionality for multimedia components, such as speakers and microphones, into a canvas. The components were represented as SVG images, and my goal was to allow users to drag items from a sidebar and drop them onto a Konva canvas, where the images would then render dynamically.

Initial Setup

I started with a React component that rendered an audio equipment list, containing draggable SVG icons:

const AudioEquipmentList = () => {
  const componentList = [
    { type: "image", url: LargeSpeakerIcon.src, component: Component1 },
    { type: "image", url: MediumSpeakerIcon.src, component: Component2 },
    { type: "rect", component: Component3 },
  ];

  return (
    <div className="grid grid-cols-3 auto-rows-fr gap-4 mb-4">
      {componentList.map((item, index) => (
        <div key={index} draggable>
          {item.component()}
        </div>
      ))}
    </div>
  );
};

The logic for drag-and-drop worked well. I stored information about the dragged item (e.g., the image source) in Redux using a dragSlice. However, rendering the image correctly on the canvas became the primary challenge.

Handling the Drop on Canvas

On the canvas, I set up a handleDropOnCanvas function that receives the image data and updates the state in Redux. Here’s a snippet of that logic:

else if (draggedItem.type.includes("image")) {
  const image = await utils.loadImg(draggedItem.imgSrc);

  const imageNode = utils.createNodeData({
    type: draggedItem.type,
    x: pointerPosition.x - image.width() / 2,
    y: pointerPosition.y - image.height() / 2,
    props: { width: image.width(), height: image.height(), src: draggedItem.imgSrc },
  });

  dispatch(canvasNodeSliceActions.addNode(imageNode));
}

At this point, the Redux store had all the necessary data, but when rendering the image node in the NodeComponent, the SVG would not appear correctly.

Initial Rendering Issue

When I attempted to render the image in the Konva canvas using the Konva.Image component, I encountered the following error:

Uncaught TypeError: Failed to execute 'drawImage' on 'CanvasRenderingContext2D'

This occurred because I was trying to pass the src string directly to the Konva.Image, which expects an HTMLImageElement or CanvasImageSource.

Solution: `useImage`

The key to solving the issue was leveraging the useImage hook provided by react-konva. This hook handles image loading and returns an HTMLImageElement, which can be directly used with Konva.Image.

Here’s how I modified the NodeComponent to render the image conditionally:

const NodeComponent = (props: NodeComponentProps) => {
  const nodeInstance = utils.createCanvasNodeInstance(props.data);
  const config = nodeInstance.getNodeConfig();

  const [image] = useImage(props.data.props.src || "");

  switch (props.data.type) {
    case "rect":
      return <Rect {...config} />;
    case "circle":
      return <Circle {...config} />;
    case "image":
      return image ? <Image image={image} {...config} /> : null;
    default:
      return null;
  }
};

Key Learning

Initially, I tried calling the useImage hook only if props.data.type === "image". This triggered an ESLint error:

React Hook "useImage" is called conditionally. React Hooks must be called in the exact same order in every component render.

To solve this, I moved the useImage hook outside the conditional block and ensured that an empty string is passed if props.data.props.src is undefined.

Conclusion

After implementing the useImage hook properly, the SVGs were rendered correctly in the Konva canvas. This journey was a great learning experience in managing drag-and-drop, handling image loading in React-Konva, and dealing with React hooks in a dynamic component rendering setup.

If you’re working with React-Konva and face similar challenges, remember:

Use the useImage hook for loading and rendering images in Konva.
Keep hooks outside of conditionals to avoid issues with React’s rendering cycle.
Ensure your image source is correctly loaded and passed as an HTMLImageElement or CanvasImageSource.

I hope this helps anyone facing similar hurdles in their projects!

27 June 2023