Create a parallax background in Flame com Flutter

Parallax backgrounds are used in all kinds of applications, not only in 2D games, but also in web pages to define background, etc; In this post we will see how to define a parallax background as background for our 2D games with Flame.

Let's start by loading the images for the parallax background:

In Flame, we have a component called ParallaxComponent that makes the process of creating a parallax effect very easy; with defining the images to use as a list:

lib/main.dart

class MyGame extends FlameGame {
  @override
  void onLoad() async {
    super.onLoad();
    add(await bgParallax());
  }

  Future<ParallaxComponent> bgParallax() async {
     ParallaxComponent parallaxComponent = await loadParallaxComponent([
      ParallaxImageData('layer06_sky.png'),
      ParallaxImageData('layer05_rocks.png'),
      ParallaxImageData('layer04_clouds.png'),
      ParallaxImageData('layer03_trees.png'),
      ParallaxImageData('layer02_cake.png'),
      ParallaxImageData('layer01_ground.png'),
    ],
        baseVelocity: Vector2(10, 0));

        return parallaxComponent;
  }
}

You will see that we have almost achieved the parallax effect, for now, all the layers move at the same speed; the baseVelocity argument allows you to define the displacement of the backgrounds, usually you want the displacement to occur on the X axis and not on the Y axis, so:

baseVelocity: Vector2(10, 0)

As homework, try different values when defining the vector and using different images (comment out and dislike some of the ParallaxImageData defined above, change the order layers) and evaluate their behavior; but, in essence, if you use high values, such as:

baseVelocity: Vector2(100, 0)

You will see a rapid displacement in the backgrounds, if you place lower values:

baseVelocity: Vector2(5, 0)

The scroll will be slower, and if you define the scroll on the Y:

baseVelocity: Vector2(5, 10)

The layers will move on the X and Y axis.

When you run the application, you should see output like the following:

Vary speed in layers

At the moment we get a somewhat boring parallax background since, although we have a background that moves, everything moves at the same speed; but, to customize this aspect, that is, that the backgrounds move at different speeds, we can use the velocityMultiplierDelta parameter, which allows moving the background images (layers) with a faster speed, the more "close" the image is image:

lib/main.dart

Future<ParallaxComponent> bgParallax() async {
    ParallaxComponent parallaxComponent = await loadParallaxComponent([
    ***
      baseVelocity: Vector2(10, 0),
      velocityMultiplierDelta: Vector2(1.1, 0));
}

With this, we will have the same effect but now the layers move at different speeds; so that you understand how this argument works, try placing higher values and you will see that the closer the layer is, the faster it will move.

Create a component class for the parallax

We can create the parallax equivalent with a component class looking like:

import 'dart:async';

import 'package:flame/components.dart';
import 'package:flame/parallax.dart';

import 'package:parallax06/main.dart';

class CandyBackground extends ParallaxComponent {
  @override
  FutureOr<void> onLoad() async {
    parallax = await gameRef.loadParallax([
      ParallaxImageData('layer06_sky.png'),
      ParallaxImageData('layer05_rocks.png'),
      ParallaxImageData('layer04_clouds.png'),
      ParallaxImageData('layer03_trees.png'),
      ParallaxImageData('layer02_cake.png'),
      ParallaxImageData('layer01_ground.png'),
    ],
        baseVelocity: Vector2(10, 0),
        velocityMultiplierDelta: Vector2(1.1, 1.1));

    return super.onLoad();
  }
}

The gameRef allows you to get a reference to the game (the MyGame class defined in main); as for the main:

lib/main.dart

import 'package:flutter/material.dart';
import 'package:flame/game.dart';

import 'package:parallax06/background/candy_background.dart';

class MyGame extends FlameGame {
  @override
  void onLoad() async {
    super.onLoad();
    add(CandyBackground());
}

And with this we have the same result as before.

This material is part of my complete course and book on Flutter Flame.