p5.js Instance Mode canvas placement and DOM encapsulation

Canvas Synchronization in Instance Mode

p5.js does not provide a native, automatic mechanism to synchronize the canvas size with a fluid parent container. Once createCanvas() is executed within the setup() function, the canvas dimensions are fixed. If the parent DOM element changes size due to CSS layout shifts or window resizing, the canvas will not automatically scale or resize to fit the new dimensions.

Updating Dimensions Without Re-instantiation

To update the canvas dimensions without destroying and recreating the p5 instance, use the resizeCanvas() method. This method allows you to modify the internal drawing surface dimensions while maintaining the current state of the sketch.

The recommended implementation involves attaching a listener to the window or using a ResizeObserver on the parent container to trigger the update. Because the sketch is in instance mode, you must call resizeCanvas() as a method of the instance object.

const sketch = (p) => {
  p.setup = () => {
    p.createCanvas(400, 400);
  };

  p.draw = () => {
    p.background(200);
    p.ellipse(p.width / 2, p.height / 2, 50, 50);
  };
};

const myP5 = new p5(sketch, 'canvas-container');

// Handle dynamic resizing
window.addEventListener('resize', () => {
  const container = document.getElementById('canvas-container');
  myP5.resizeCanvas(container.clientWidth, container.clientHeight);
});

Technical Considerations and Constraints

• Coordinate Distortion: Avoid using CSS width: 100% or height: 100% on the canvas element itself. This scales the visual output without updating the internal p5 coordinate system, leading to blurred pixels and distorted aspect ratios.
• Performance Overhead: Frequent calls to resizeCanvas() (such as every single frame of a window resize event) can cause performance degradation. Implementing a debounce function is recommended for production environments.
• DOM Encapsulation: Passing a selector or element to the p5() constructor ensures the canvas is appended to that specific container, but it does not grant the instance awareness of that container's CSS constraints.

To provide a more specific optimization strategy, please clarify if the parent container is resized by the browser window or by a JavaScript-driven UI transition (e.g., a collapsible sidebar).