Jump to content

Arcade physics body of child lagging behind when accelerating its parent


Recommended Posts

Version 2.9.1 (phaser-ce)

I'm seeing some unexpected behavior with the physics body of child sprites lagging behind when accelerating the parent. So when debugging the bodies, they appear slightly offset in the opposite direction of the movement:


This is the code for an example I made to illustrate my problem: 

var game = new Phaser.Game({
  state: {
    preload: function() {
      this.load.baseURL = 'https://examples.phaser.io/assets/';
      this.load.crossOrigin = 'anonymous';
      this.load.atlas('spritesheet', 'atlas/megasetHD-1.png', 'atlas/megasetHD-1.json');
    create: function() {
    update: function() {
      this.vegContainer.body.acceleration.y = 50 * this.time.physicsElapsedMS;
    render: function() {
    createVegetables: function() {
      // Create veg groups.
      this.melons = this.add.group();
      this.mushrooms = this.add.group();
      // Container.
      this.vegContainer = this.add.graphics();
      const height = 120;
      const x = 350;
      for (let y = 0; y > -1000; y--) {
        let sprite;
        let isMelon = Math.random() > .5;
        if (isMelon) {
          sprite = this.melons.create(x, height * y, 'spritesheet', 'melon');
        } else {
          sprite = this.mushrooms.create(x, height * y, 'spritesheet', 'mushroom');
      // Enable physics on container and all children.
      this.vegContainer.body.maxVelocity.y = 800;

and this is the code pen link.

It will work as expected if I accelerate the groups individually but this is not ideal as there are quite a lot of groups in the game. Is this a bug or is it working as expected?


Link to comment
Share on other sites

Part of the difference is the WEBGL debug canvas, which can be one frame behind (I think). You can temporarily use CANVAS.

The other part is normal, because the children's physics bodies are repositioned only during preUpdate (using the sprites' positions during the last render). So at render time those physics bodies are slightly behind their sprite's positions. It doesn't really matter for rendering (where physics bodies are irrelevant), but it's a little confusing to look at.

I think you might have fewer surprises if you accelerate the food one by one though. :)

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Create New...