What is a Group?

In p5play a Group is a collection of and blueprint for sprites with similar traits and behaviors. For example the dots in Pac-Man!

The group.length property can be used to check how many sprites are in a group. In this example the while loop condition is true as long as the dots group has less than 24 sprites.

In the mini example, new dots.Sprite creates a sprite that inherits the dots group's color, y position, and diameter. Each dot is assigned a unique x position.

I call this "soft inheritance" because a group acts as a blueprint for new group sprites.

You can access a sprite in a group by index because groups are arrays. You can use any of the standard JavaScript array methods on a group.

Setting a group's property to a different value will affect all the sprites in the group! I call this "dynamic inheritance".

Using movement functions like moveTowards on a group, will cause all the sprites in a group to move.

Arrow function property setters

If you set a group property to an arrow => function, each new sprite created using that group will use the function to evaluate the property.

When group.amount is adjusted, the group will automatically create or remove sprites to match the set amount.

In this mini example, each gem sprite is assigned a random position on the canvas.

Indexed arrow function setters

Arrow setters can use the sprite's index in the group!

The index, i, is given as an input parameter to the group's arrow setters. It can be used to calculate the new group sprite's properties.

Collisions and Overlaps

Collision and overlap functions aren't just for detecting events between two sprites. You can also check for collisions and overlaps between sprites and groups or between groups. The functions are:

collides, colliding, collided
overlaps, overlapping, overlapped

Instead of using these functions in if statements, you can provide them with a callback function as a second parameter. The callback function will run when the collision or overlap event occurs. The callback function receives, as inputs, two sprites.

In this mini example the callback function receives the player sprite and the gem sprite in the gems group that the player overlaps. That gem gets collected (removed).

allSprites Group

p5play creates an allSprites group that contains all the sprites in a sketch.

Custom Properties

You can add your own properties to sprites and groups, just like with any other JavaScript object!

Also when you add custom properties to a group, they will be inherited by new group sprites. You can even use arrow functions as property setters.

Sub Groups

In this mini example there are two sub groups of the boxes group: smallBoxes and bigBoxes.

New sprites created using the bigBoxes group will inherit traits from the boxes group but not from the smallBoxes groups.

The boxes group contains all the sprites in the smallBoxes and bigBoxes groups.

The remove function removes the group itself, only use it if you don't want to use the group again. If you just want to remove all the sprites from a group, use the removeAll function.

Culling

By default, sprites are removed when they go 10000 pixels offscreen relative to the camera's position. This is to prevent the world from getting too big, which would slow down the physics simulation.

To change this, set allSprites.autoCull = false or use the cull function to set a different cull boundary. Note that it can even cull sprites that don't have a physics collider.

Sprites that cross the cull boundary are removed by default. As the last input parameter to the cull function, you can insert a callback function. When called, it receives the sprite that was culled and a total count of how many sprites were culled on that frame.

Note that in this example, the amount of balls decreases if more than one ball is culled in one frame.

life

Another way to limit how long a sprite exists is to set its life property, which is the number of frames that the sprite exists for. When the sprite's life reaches 0, it will be removed. This is useful for creating temporary objects like projectiles and force fields.

Try out this little game! Click the mouse to create a beach ball and try keeping it in the air with the water stream.

Draw

Just like with the sprite.draw function, you can use group.draw to manually control when groups are drawn inside the p5.js draw loop.

Any sprites not drawn manually will be automatically drawn at the end of the p5.js draw loop, unless their autoDraw property is set to false.

Note that if you want to manually draw sprites or groups and use the camera, you'll have to manually turn the camera on and off.

Update

The group.update function runs the sprite.update function of every sprite in the group. To prevent automatic updating set autoUpdate to false.

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