Three.js memory allocation & workflow question

Question

Let’s say I want to make 100 objects - for example cars, like the one you see here:

This car is currently comprised of 5 meshes: one yellow Cube and four blue Spheres

What I’d like to know is what would be the most efficient/correct way to make 100 of these cars - or maybe 500 - in terms of memory management/ CPU performance, etc.

The way I’m currently going about doing this is as follows:

1. Make an empty THREE.Group called “newCarGroup” -
2. Create the yellow rectangular Mesh for the body of the car - called “carBodyMesh”
3. Create four blue Sphere Meshes for the Tires called “tire1Mesh”, “tire2Mesh”, “tire3Mesh”, and “tire4Mesh”
4. Add the Body and the four Tires to the “newCarGroup”
5. And finally, in a FOR loop, create/instantiate 100 “newCarGroup” objects, adding each one to the SCENE at a random position

The code is below.

It's working perfectly well right now, but I’d like to know if this is the “proper”/best way to do this?
Consider it’s possible I might end up needing 1,000 cars - or 5,000 cars. So will this scale properly?

Also, I need to add more objects to the car: like 4 windows - actually make that 6 windows, to also include the front and back windshields, then four headlights, etc. So the final Car Object alone may end up being comprised of 20 meshes - or more.

Being that I’m kinda new to THREE.JS I wanna make sure I develop good habits and go about this sort of thing the right way.

Here’s my code:

        function makeOneCar() {
            var newCarGroup = new THREE.Group();

            // 1. CAR-Body:
            const bodyGeometry = new THREE.BoxGeometry(30, 10, 10);
            const bodyMaterial = new THREE.MeshPhongMaterial({ color: "yellow" } ); 
            const carBodyMesh = new THREE.Mesh(bodyGeometry, bodyMaterial);

            // 2. TIRES:
            const tireGeometry = new THREE.SphereGeometry(2, 16, 16);;
            const tireMaterial = new THREE.MeshPhongMaterial( { color: "blue" } ); 
            const tire1Mesh = new THREE.Mesh(tireGeometry, tireMaterial);
            const tire2Mesh = new THREE.Mesh(tireGeometry, tireMaterial);
            const tire3Mesh = new THREE.Mesh(tireGeometry, tireMaterial);
            const tire4Mesh = new THREE.Mesh(tireGeometry, tireMaterial);

            // TIRE 1 Position:
            tire1Mesh.position.x = carBodyMesh.position.x - 11;
            tire1Mesh.position.y = carBodyMesh.position.y - 4.15;
            tire1Mesh.position.z = carBodyMesh.position.z + 4.5;

            // TIRE 2 Position:
            tire2Mesh.position.x = carBodyMesh.position.x + 11;
            tire2Mesh.position.y = carBodyMesh.position.y - 4.15;
            tire2Mesh.position.z = carBodyMesh.position.z + 4.5;

            // TIRE 3 Position:
            tire3Mesh.position.x = carBodyMesh.position.x - 11;
            tire3Mesh.position.y = carBodyMesh.position.y - 4.15;
            tire3Mesh.position.z = carBodyMesh.position.z - 4.5;

            // TIRE 4 Position:
            tire4Mesh.position.x = carBodyMesh.position.x + 11;
            tire4Mesh.position.y = carBodyMesh.position.y - 4.15;
            tire4Mesh.position.z = carBodyMesh.position.z - 4.5;

            // Putting it all together:
            newCarGroup.add(carBodyMesh);
            newCarGroup.add(tire1Mesh);
            newCarGroup.add(tire2Mesh);
            newCarGroup.add(tire3Mesh);
            newCarGroup.add(tire4Mesh);

            // Setting (x, y, z) Coordinates - RANDOMLY
            let randy = Math.floor(Math.random() * 10);
            let newCarGroupX = randy % 2 == 0 ? Math.random() * 250 : Math.random() * -250;
            let newCarGroupY = 0.0; 
            let newCarGroupZ = randy % 2 == 0 ? Math.random() * 250 : Math.random() * -250;

            newCarGroup.position.set(newCarGroupX, newCarGroupY, newCarGroupZ)

            scene.add(newCarGroup);
        }




        function makeCars() {
            for(var carCount = 0; carCount < 100; carCount ++) {
                makeOneCar();
            }
        }

Answer 1

I’d like to know if this is the “proper”/best way to do this?

This is subjective. You say the method works great for your current use-case, so for that use-case, it is fine.

So will this scale properly?

The simple answer is: No. The more complex answer is: ...not really.

You're re-using the geometry and materials, which is good. But every Mesh you create has meta information surrounding it, which adds to your overall memory footprint.

Also, every standard Mesh you add incurs what is known as a "draw call", which is the GPU drawing that particular shape. Instead, take a look at InstancedMesh. This allows the GPU to be given instructions on how to draw the shape throughout the scene once. Yes, rather than drawing each cube individually, the GPU can draw all the cubes at the same time, and they can even have different colors and transformations. There are limitations to this class, but it's a good starting point to understanding how instancing works.