Activity: Generate Sprites using ||sprites:create|| and ||sprites:on created||
Many games need to spawn sprites for the player to do things like collect coins or avoid oil spills.
We will use the ||sprites:set mySprite to|| block from the Sprites menu to spawn a new empty sprite, with nothing in it yet. Then we can use an ||sprites:on created|| event to set the image and a random position for newly generated sprites.
The ||sprites:on created|| block uses the sprite’s ||sprites:kind|| so we can give our new sprites the exact attributes we want, like an image, velocity, or position.
Concept: Create with on created event
Example #1: Random clouds
This example uses the ||sprites:on created|| event to set the sprite image and location after a sprite of a particular ||sprites:kind|| is spawned.
- Review the code below
- Create a new project and name it “spawnCloud”
- Create the sample code and run the code
- Carefully examine the
||sprites:sprite of kind||oval in the||variables:set cloud to||blocks and the||sprites:on created||event
namespace SpriteKind {
export const Helicopter = SpriteKind.create();
export const Cloud = SpriteKind.create();
}
let agent: Sprite = null
let cloud1: Sprite = null
let cloud2: Sprite = null
controller.up.onEvent(ControllerButtonEvent.Pressed, function () {
agent.vy += -1
})
controller.down.onEvent(ControllerButtonEvent.Pressed, function () {
agent.vy += 1
})
controller.left.onEvent(ControllerButtonEvent.Pressed, function () {
agent.vx += -1
})
controller.right.onEvent(ControllerButtonEvent.Pressed, function () {
agent.vx += 1
})
sprites.onCreated(SpriteKind.Cloud, function (newCloud) {
newCloud.setImage(img`
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. . . . 1 1 1 1 1 8 . . . . . .
. . . 1 1 8 8 8 1 1 1 1 1 1 . .
. 8 1 1 8 8 8 8 8 8 8 8 8 1 1 .
. 1 8 8 8 1 8 8 8 1 1 8 8 8 1 .
1 1 8 8 1 1 1 1 1 8 8 8 1 1 1 .
1 1 8 8 8 8 8 1 1 8 1 8 1 1 . .
. 1 1 1 1 8 8 8 8 8 8 8 1 8 . .
. . . . 1 1 8 8 1 1 8 8 1 . . .
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`)
newCloud.x = randint(16, scene.screenWidth() - 16)
newCloud.y = randint(20, scene.screenHeight() - 75)
})
sprites.onOverlap(SpriteKind.Helicopter, SpriteKind.Cloud, function (sprite, otherSprite) {
sprite.x += -1 * sprite.vx
sprite.y += -1 * sprite.vy
sprite.vx = 0
sprite.vy = 0
otherSprite.y += -1
pause(100)
otherSprite.y += 1
})
game.splash("Generated Clouds", "on Sprite created")
scene.setBackgroundColor(9)
agent = sprites.create(img`
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. . . . . f f f f . . . . . . . . . f f f f f f f . . . . . . .
. . . . . . . f f f f f f f f f f f f f . . . . . . . . . . . .
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. . . . f . . . . . . . . . e . . e e f f 1 1 . . . . . . . . .
. . f f f f f f f f . . . . e e e 2 f . 1 1 1 1 . . . . . . . .
. . . . . f . . . . . . e e e 2 2 2 f 1 1 1 1 1 . . . . . . . .
. . . . . f . . . e e e 2 2 2 2 2 2 f 1 1 1 1 1 e . . . . . . .
. . . . . f e e e e 2 2 2 2 2 2 2 2 f f 1 1 f 2 e . . . . . . .
. . . . . e e 2 2 2 2 2 2 2 2 2 2 2 f f f f f 2 e . . . . . . .
. . . . . e 2 2 2 2 2 2 2 2 2 2 2 2 f f f f f 2 e . . . . . . .
. . . . . e e 2 2 2 2 2 2 2 2 2 2 2 f f f f f 2 e . . . . . . .
. . . . . . e e 2 2 2 2 2 2 e 2 2 2 2 2 2 f f 2 e . . . . . . .
. . . . . . . e e 2 2 2 2 2 e e 2 2 2 2 2 2 2 e e . . . . . . .
. . . . . . . . e e e e 2 e e e 2 2 2 2 2 2 e e . . . . . . . .
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. . . . . . f f f f f f f f f f f f f f f f f f f f . . . . . .
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`, SpriteKind.Helicopter)
cloud1 = sprites.create(img`
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`, SpriteKind.Cloud)
cloud2 = sprites.create(img`
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`, SpriteKind.Cloud)Student Task #1: More Random Clouds
The ||sprites:on created|| event allows us to set code to run whenever a new sprite is created. This is used to create new clouds multiple times with the same code. Now we will create new clouds with ||variables:set cloud to|| blocks with empty image editors.
- Start with example #1 or your own similar code
- Add two more
||variables:set cloud to||blocks for clouds - Add a new
||variables:set mySprite to||block for a different||sprites:kind||. Use the||sprites:on created||event to- set an image for the sprite that is created (for example, a bird or a butterfly)
- set the sprite to be in a random position
- Use
||variables:set mySprite to||blocks to create at least five of the kinds - Challenge: create an event for the
||sprites:Helicopter||overlap with the new||sprites:kind||that has an action that gives the new||sprites:kind||a fast velocity so that it will fly off the screen after they overlap
What did we learn?
- Describe how a
||sprites:kind||label is used in generating a sprite by creating an empty sprite block. - Explain what the
||sprites:on created||block does for you.