Disabling gravity for a specific object in Matter.js

Question

I'm working on a project using Matter.js where I want gravity enabled in general, but I want to be able to disabled and re-enable it for a single object at certain times. I do not want to set that object as static, because I want the physics engine to handle it in other ways, I just don't want gravity to affect it.

I found this question that deals with disabling gravity in general, but as I said I want gravity to work for most objects. Is there a simple way to do this?

could you load the object into a new world that is contained within the main world? from browsing the API quickly it looks like this would be the only way http://brm.io/matter-js/docs/classes/World.html — tmaxxcar, Apr 06 '16 at 23:33

Derek · Answer 1 · 2019-10-28T13:33:19.293

7

Here is a simple code snippet that you could have toggle on/off to accomplish what you're asking (where body is the object that should ignore gravity, and noGravity is a boolean that can be toggled to turn it on and off):

Events.on(engine, 'beforeUpdate', function() {
    var gravity = engine.world.gravity;

    if (noGravity) {
        Body.applyForce(body, body.position, {
            x: -gravity.x * gravity.scale * body.mass,
            y: -gravity.y * gravity.scale * body.mass
        });
    }
});

edited Oct 28 '19 at 13:33

answered Feb 02 '18 at 15:56

Derek

298
3
12

Extremely helpful answer, thanks. Fixed the problem I was having. – shell Apr 01 '18 at 22:03
1

This just makes my body spin around in one spot. Help? – Sam Sverko Jul 17 '19 at 19:04
2

@SamSverko same here. Replace `{ x: 0, y: 0 }` with `body.position` to fix. (@Derek can you update the answer?) – Harold Cooper Oct 27 '19 at 14:32

score 6 · Answer 2 · answered Oct 18 '16 at 22:44

Disable the built in gravity and then apply your own selectively, something like this but filter only the bodies you want:

engine.world.gravity.scale = 0;

Events.on(engine, 'beforeUpdate', function() {
    var bodies = Composite.allBodies(engine.world);

    for (var i = 0; i < bodies.length; i++) {
        var body = bodies[i];

        if (body.isStatic || body.isSleeping)
            continue;

        body.force.y += body.mass * 0.001;
    }
});

Hexus · Answer 3 · 2018-04-20T21:34:49.300

3

I know this is an old question, but nowadays you can use this:

body.ignoreGravity = true;

edited Apr 20 '18 at 21:34

answered Apr 20 '18 at 20:43

Hexus

340
4
9

As of which version? – wizzwizz4 Jul 20 '19 at 15:34
3

Turns out I was wrong, this is a Phaser specific feature and not supported directly by Matter.js. https://github.com/liabru/matter-js/issues/523 – Hexus Jul 23 '19 at 13:05

score 1 · Answer 4 · answered Jan 14 '21 at 23:39

I found that was very easy to implement that. Just look for the Engine._bodiesApplyGravity function on the Matter source code and just put whatever condition you need for a body to be excluded.

        Engine._bodiesApplyGravity = function (bodies, gravity) {
            var gravityScale = typeof gravity.scale !== 'undefined' ? gravity.scale : 0.001;

            if ((gravity.x === 0 && gravity.y === 0) || gravityScale === 0) {
                return;
            }

            for (var i = 0; i < bodies.length; i++) {
                var body = bodies[i];

                // I just added body.ignoreGravity
                if (body.isStatic || body.isSleeping || body.ignoreGravity)  
                    continue;

                // apply gravity
                body.force.y += body.mass * gravity.y * gravityScale;
                body.force.x += body.mass * gravity.x * gravityScale;
            }
        };

What's the best practice to apply this override, without actually touching the original module? — Kalnode, May 06 '23 at 22:31

score 0 · Answer 5 · answered Oct 09 '16 at 22:13

This seems to provide a counter force. I'm not sure where the 200 is coming from it just worked. Maybe the engine calculates force twice a cycle.

playerBody.force.y = -engine.world.gravity.y / 200;

You will have to run it every cycle to keep it up.

score 0 · Answer 6 · answered May 07 '20 at 01:16

0

In my case I wanted an object to follow the mouse. Setting isStatic: true made gravity not apply to give me full control over the object's position.

answered May 07 '20 at 01:16

Zach Saucier

24,871
12
85
147

score -1 · Answer 7 · answered Aug 26 '19 at 16:12

-1

there is an official working example

this.matter.add.image(100, 100, 'block').setIgnoreGravity(true);

ignoring gravity phaser3 matter physic

answered Aug 26 '19 at 16:12

mustafa kemal tuna

861
8
18

4

Phaser != Matter – Zach Saucier May 07 '20 at 00:52

Disabling gravity for a specific object in Matter.js

7 Answers7