pxt-calliope/docs/projects/snap-the-dot.md

Snap the dot

Introduction @unplugged

Snap the dot is a kill game where the player has to press A exactly when the dot is in the center of the screen.

This is a tutorial to learn how to use the game engine.

Create a sprite @fullscreen

Drag a ||game:create sprite|| block in the workspace. A sprite is a single pixel that can move on the screen. It has a x, y position and a direction.

let sprite: game.LedSprite = null
sprite = game.createSprite(2, 2)

Move the dot @fullscreen

The sprite starts in the center facing right. Drag a ||game:move|| block in the forever to make it move. Notice how it moves to the right but does not bounce back.

let sprite: game.LedSprite = null
sprite = game.createSprite(2, 2)
basic.forever(function () {
    sprite.move(1)
})

Bounce @fullscreen

Drag a ||game:ifOnEdgeBounce|| block to make the sprite bounce on the side of the screen. Add also a ||basic:pause|| block to slow down the sprite.

let sprite: game.LedSprite = null
sprite = game.createSprite(2, 2)
basic.forever(function () {
    sprite.move(1)
    sprite.ifOnEdgeBounce()
    basic.pause(100)
})

Test and download

Use the simulator to find the best speed. If you have a @boardname@, press Download to try it out on the device.

Button handling @fullscreen

When A is pressed, we test if the sprite is in the center or not.

Drag a ||input:on button pressed|| block to handle the A button. Drag a ||logic:if|| block and test if ||game:x|| is equal to 2.

let sprite: game.LedSprite = null
input.onButtonPressed(Button.A, function () {
    if (sprite.get(LedSpriteProperty.X) == 2) {
    } else {
    }
})
sprite = game.createSprite(2, 2)
basic.forever(function () {
    sprite.move(1)
    basic.pause(100)
    sprite.ifOnEdgeBounce()
})

Score and game over

Drag a ||game:add score|| and a ||game:game over|| block to handle success (sprite in the center) and failure (sprite not in the center)

let sprite: game.LedSprite = null
input.onButtonPressed(Button.A, function () {
   if (sprite.get(LedSpriteProperty.X) == 2) {
       game.addScore(1)
   } else {
       game.gameOver()
   }
})
sprite = game.createSprite(2, 2)
basic.forever(function () {
   sprite.move(1)
   basic.pause(100)
   sprite.ifOnEdgeBounce()
})

Test and download

Your game is ready! Use the simulator to find the best speed. If you have a @boardname@, press Download to try it out on the device.