💡 Dev Tip March 2026 ~7 min read

Canvas 2D vs Three.js — When to Choose Each

Not every simulation needs WebGL. Here's the full decision framework I use when starting a new simulation — and why about half of this site's 225 simulations are pure Canvas 2D.

The Real Question

When you start a new simulation, the choice between Canvas 2D and Three.js is rarely about "which is better." It's about what the simulation actually needs. Canvas 2D's 2D drawing API is surprisingly capable, and the rendering thread stays on the CPU — which is sometimes exactly what you want when your physics also runs on the CPU and you need tight synchrony.

Three.js hands rendering to the GPU via WebGL. That's the right call when you have tens of thousands of particles, volumetric effects, or real-time 3D geometry. But it costs: more code, a larger dependency, and a higher debugging overhead.

Head-to-Head Comparison

Criterion Canvas 2D Three.js (WebGL)
Setup complexity 3 lines of code ~20 lines minimum
Particle count (60 FPS) ~2 000–5 000 50 000–1 000 000+
Dependency size 0 KB (browser built-in) ~150 KB (Three.js core)
Custom shaders (GLSL) Not available Full GLSL support
3D rendering Manual projection math Native 3D scene graph
ImageData / pixel ops Fast, direct access Requires render target readback
Text rendering fillText() — trivial TextGeometry / Sprites — complex
Interactivity (click/drag) Simple coordinate math Raycasting required
Debugging DevTools, breakpoints work everywhere GLSL errors are cryptic
Mobile performance Acceptable for small N GPU handles big N well
Postprocessing (bloom, blur) Manual, slow EffectComposer + built-in passes

When Canvas 2D Wins

Choose Canvas 2D when:

When Three.js Wins

Switch to Three.js when:

Real Examples from This Site

Of the 225 simulations here, roughly half use Canvas 2D and half use Three.js. Here's the split:

A good heuristic: start every simulation in Canvas 2D. If, after a working prototype, you're hitting a framerate wall or need a 3D view, migrate to Three.js. You'll only add the extra complexity when it's genuinely needed — and you'll understand the algorithm before fighting the renderer.

Starting with Canvas 2D, Migrating Later

The migration path from Canvas 2D to Three.js is usually straightforward if you separate your simulation logic from rendering from the start. Keep the physics update in a pure function that takes state and returns new state. The renderer is just a consumer of that state. 

// Good structure — renderer is swappable
function updatePhysics(state, dt) { /* pure logic */ return newState; }
function renderCanvas2D(ctx, state) { /* draws to canvas */ }
function renderThreeJS(scene, state) { /* updates Three.js objects */ }

// In rAF loop:
state = updatePhysics(state, dt);
renderCanvas2D(ctx, state);  // swap to renderThreeJS when ready

The trap to avoid: mixing physics calculations into draw calls. Once you do ctx.moveTo(particle.x += vx * dt, ...) inside a draw loop, migration becomes a full rewrite instead of a render swap.

Decision Checklist

Canvas 2D Three.js WebGL Dev Tip Performance