Activity: Sprite Overlap & Events - Part 2

We use ||sprites:kind|| to give a label to our sprites so we can define how one ||sprites:kind|| of sprite will react when moving on top of another ||sprites:kind|| of sprite.

In the previous activity, all “Cloud” ||sprites:kind||‘s respond with the same action when overlapped with a “Helicopter” ||sprites:kind||.

By making several cloud shaped sprites with the same ||sprites:kind|| of Cloud, we can write code so that all of the clouds interact with the Helicopter in the same way with an overlap event.

In this activity, the student will continue to work with:

• ||sprites:on overlap event|| with a ||sprites:kind|| applied to several identical sprites
• Overlap events

Concept: ||sprites:Kind|| Overlap Event “bump” action

Having sprites bump rather than pass over each other is useful game behavior for a ||sprites:kind|| overlap event. One way to simulate a bump is:

1. Move the sprite in the opposite direction after the overlap (we will make it bump backwards). The faster we bump, the farther we move away from the overlap object
2. Stop the sprite
   • Set ||sprites:vx|| and ||sprites:vy|| to 0
   • Change x position by (-1) * (||sprites:vx||)
   • Change y position by (-1) * (||sprites:vy||)
3. Shake the stationary object (cloud)
   • Move 1 pixel (in any direction)
   • ||loops:pause||
   • Move back

Example #1: Bump action from overlap event

1. Review the code below
2. Create the sample code and run the code
3. Save the code for the task (name it “copterBump1”)
4. Look at the overlap event - note which sprite is named ||variables:sprite|| and which is ||variables:otherSprite||, and how the code creates the bump behavior

Helicopter Example

namespace SpriteKind {
    export const Helicopter = SpriteKind.create();
    export const Cloud = SpriteKind.create();
    export const LandingPad = SpriteKind.create();
}
let cloud3: Sprite = null
let cloud2: Sprite = null
let cloud1: Sprite = null
let copter: Sprite = null
let landing: Sprite = null
// Control the copter with the + pad
controller.right.onEvent(ControllerButtonEvent.Pressed, function () {
    copter.vx += 1
})
controller.left.onEvent(ControllerButtonEvent.Pressed, function () {
    copter.vx += -1
})
controller.up.onEvent(ControllerButtonEvent.Pressed, function () {
    copter.vy += -1
})
controller.down.onEvent(ControllerButtonEvent.Pressed, function () {
    copter.vy += 1
})
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("Cloud Bump", "control pad flying")
scene.setBackgroundColor(9)
copter = sprites.create(img`
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`, SpriteKind.Helicopter)
copter.setFlag(SpriteFlag.StayInScreen, true)
// Create and place "clouds"  Sprites
cloud1 = sprites.create(img`
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`, SpriteKind.Cloud)
cloud1.x = 20
cloud1.y = 30
cloud2 = sprites.create(img`
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`, SpriteKind.Cloud)
cloud2.x = 50
cloud2.y = 65
cloud3 = sprites.create(img`
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`, SpriteKind.Cloud)
cloud3.x = 100
cloud3.y = 40

landing = sprites.create(img`
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`, SpriteKind.LandingPad)
landing.y = 125

Student Task #1: Soft Landing

There is a “T” shaped landing area at the bottom of the example. The helicopter sprite should not go through the landing pad, it should land!

1. Starting with example #1, replace the helicopter motion with the short method using ||controller:dx (left-right buttons)||
2. Review the rest of the code, and then add an ||sprites:on overlaps|| event for when the helicopter overlaps with the landing (note the ||sprites:kind|| of ||sprites:LandingPad||)
3. The block of code in the overlap event should stop the helicopter velocity motion (setting both vx and vy to zero) and then change the helicopter position up 2 pixels so it isn’t overlapping any more
4. Challenge: add a new sprite and ||sprites:kind|| to the screen (for example, a mountain or a tree) and set the overlap action to make the helicopter sprite have an erratic motion after an overlap. This should require 3 or more changes in position and/or velocity

Student Task #2: Add a new unique sprite with ||sprites:kind|| of ||sprites:Cloud||

1. Starting with example code or task #1
2. Add a new sprite that looks nothing like a cloud (for example, a hat or a tree)
3. Make sure the new sprite has ||sprites:kind|| of “Cloud” even though it is not a cloud
4. Position the new sprite so it is not touching any other sprite
5. Challenge: add another Sprite that looks different from the previous new sprite and give it a ||sprites:kind|| other than ||sprites:Cloud|| and make sure it has a unique overlap event action (e.g. - might say something new)
6. Test the overlaps on the new sprite(s)

What did we learn?

1. Describe how a ||sprites:kind|| can improve code (for example, how it can make programming easier, more powerful, more efficient, …).
2. Explain why in creating a “bump” effect negative X and Y velocities are used to change the X and Y positions.

Teacher Material