How to Reuse Matter.Vector Instances in Matter.js

High performance in web physics simulations often degrades due to garbage collection (GC) pauses caused by frequent object creation inside the update loop. In Matter.js, vector calculations are among the most frequent operations, typically instantiating new coordinate objects every frame. By pre-allocating dedicated Matter.Vector instances and utilizing Matter.js's built-in target parameters or direct property mutation, you can completely eliminate runtime allocations and maintain a stable, stutter-free frame rate.

The Allocation Bottleneck

By default, helper methods such as Matter.Vector.create(x, y) or standard operations like Matter.Vector.add(v1, v2) create and return a new { x, y } object literal. When this occurs hundreds or thousands of times per second across active rigid bodies, the JavaScript runtime allocates memory rapidly, triggering periodic garbage collection cycles that drop frame rates.

Utilizing Output Targets in Matter.Vector Methods

Many developers overlook that Matter.js mathematical operations accept an optional output vector parameter. Instead of returning a newly allocated object, the method writes the calculation results directly into the provided instance.

Methods supporting an output vector include:

Implementing Pre-Allocated Scratchpad Vectors

To avoid allocation during simulation ticks, create module-level or closure-scoped scratchpad vectors once during application initialization. Reuse these references exclusively inside your loop.

// Pre-allocate scratchpad vectors outside the game loop
const scratchA = Matter.Vector.create(0, 0);
const scratchB = Matter.Vector.create(0, 0);
const forceTarget = Matter.Vector.create(0, 0);

function applyCustomForce(body, targetPosition) {
  // Calculate displacement without allocating: scratchA = targetPosition - body.position
  Matter.Vector.sub(targetPosition, body.position, scratchA);

  // Normalize the displacement vector in-place: scratchB = normalise(scratchA)
  Matter.Vector.normalise(scratchA, scratchB);

  // Scale direction by force magnitude: forceTarget = scratchB * 0.005
  Matter.Vector.mult(scratchB, 0.005, forceTarget);

  // Apply the resulting force directly
  Matter.Body.applyForce(body, body.position, forceTarget);
}

Direct Property Mutation

When performing simple assignments, avoid calling Vector.create() to update coordinates. Mutate the existing vector's x and y properties directly:

// Inefficient (allocates a new object)
body.velocity = Matter.Vector.create(0, 5);

// Efficient (zero allocation)
body.velocity.x = 0;
body.velocity.y = 5;

Implementing a Vector Pool for Dynamic Operations

For systems where vector requirements scale dynamically (such as particle effects or raycasting), implement a fixed-size pool to handle temporary allocations without invoking the garbage collector:

class VectorPool {
  constructor(size = 50) {
    this.pool = Array.from({ length: size }, () => Matter.Vector.create(0, 0));
    this.index = 0;
  }

  get(x = 0, y = 0) {
    if (this.index >= this.pool.length) {
      this.index = 0; // Wrap around for single-frame scratchpads
    }
    const vec = this.pool[this.index++];
    vec.x = x;
    vec.y = y;
    return vec;
  }

  reset() {
    this.index = 0;
  }
}

// Reset the pool pointer at the start of each frame
Events.on(engine, 'beforeUpdate', () => {
  vectorPool.reset();
});

Using pre-allocated scratchpad instances, taking advantage of the output parameter in Matter.Vector methods, and mutating coordinates directly will remove memory pressure from the browser's GC, ensuring consistent simulation performance under heavy physics loads.