Font & Particle Collisions: A JavaScript Canvas Experiment

Originally published: August 15th, 2015. Updated on: April 29th, 2025.

I've recently been fascinated by collision detection in graphics and real-time animation, especially applying it to web-based graphics. This demo explores particle collisions against standard web fonts rendered onto an HTML <canvas> element.

You can see the updated version of this here

Collision detection is the process of figuring out how objects in a scene interact with each other. Applying realistic animation effects based on these interactions can create the illusion of real-world physics – think snowflakes settling on a surface or sparks from a fire.

In this code sample, I wanted to see how I could simulate collisions between point particles and text entered into an input box. Specifically, I aimed to dynamically adjust the font, text, and the properties (position, velocity) of the particles emitted into the scene.

Feel free to play with the animation's parameters using the controls below the demo (if available in the embedded version). Adjust the text, size, and font choice to see how the particles react.

Some Technical Notes

Simulating these particle collisions involved generating a collision matrix for the text area. Each particle can then refer to this matrix to determine if it has hit the text.

How it works:

1. The text is drawn onto the HTML canvas.
2. The pixel data for the text area is extracted using the canvas getImageData() method. This gives an array containing the Red, Green, Blue, and Alpha (RGBA) values for every single pixel.
3. This data is processed to determine which pixels belong to the "font" and which are empty space ("not font"). This forms the basis of the collision matrix.

This animation uses a very basic implementation of this matrix. Technically speaking, there's plenty of room for improvement. Aesthetically, though, you can see the particles interacting fairly cleanly with the font shapes. The effect is pleasing, even if not perfectly physically accurate. The current code basically says, "If a particle hits the font area, send it off in another random direction until it eventually settles." It looks nice enough for a visual experiment.

Performance Considerations

Some performance optimizations were made. For example, since we know the text only occupies a specific, calculable portion of the canvas (usually centered), we don't need to perform collision checks for particles in the empty areas. Basically, we skip calculations where we know no text exists.

Also, the collision matrix doesn't necessarily need to check every single pixel. It can be calculated using a less precise grid. Instead of checking 1x1 pixels, we could subdivide the canvas into larger squares (e.g., 4x4 pixels). We then check, "Does this 4x4 area contain any part of the font?" If yes, process collision logic for particles entering that area. This significantly reduces the number of checks needed.

An Aesthetic Note…

For visual experiments like this, where the focus is on appearance rather than strict physical accuracy, further algorithmic refinement might be unnecessary. This brings up an interesting point about time vs. benefit. You can spend a lot of time perfecting visual effects or complex features, but based on the law of diminishing returns, that extra time doesn't always equate to a proportionally better result, especially from a viewer's perspective.

This applies to web development work too. There's often no point spending 50% more time on a complex feature if that extra effort won't significantly improve the user experience or visual appeal. It's about knowing when to stop!

Further Development Ideas

Of course, for completeness and personal curiosity, I'll likely revisit this code someday. Potential enhancements include:

1. Accurate Collision Response: Calculate the 2D normal vector at different points on the font's surface. This would allow particles to bounce off more realistically and flow over the surface more cleanly, instead of just scattering randomly.
2. Performance Improvements: Explore more efficient data structures for storing and looking up the collision data (currently using a simple JavaScript array representing the grid). Quadtrees or other spatial partitioning methods might help.
3. Physics Refinements: Implement more realistic physics, like friction or particle-particle interactions (though this could become computationally expensive).