In this add-on, you will create a power-up that makes the racer shrink so it can avoidobstacles more easily. To start, click the “choose sprite fromlibrary” button to add a new sprite to be your power up. You can choose any sprite.
This example will use an apple.
Use the grow and shrink tools to make the sprite the right size for your game. Then,click on the “i” next to the sprite, and name it “power up.”
To make the power up sprite move across the screen like the obstacle sprite, copy allthe code from the obstacle sprite to the power up sprite. First, select the obstacle sprite.
Then, drag each code stack over to the power up sprite. When you select the power up sprite,you’ll see that all the code has copied over.
The power-up only has one costume, so get rid of the “switch costume to” block atthe top of this stack. Drag the bottom part of the stack away, drag the block back intothe block menu, then snap the rest of the stack back together.
Test your code by clicking the flag. Great! Power up sprites are moving across the stagealong with obstacle sprites. Next, program the racer to shrink when ittouches the power up. Select the racer. Then, open the “looks” menu, and drag out a“change size by 10” block. Change its value to negative 10, then click on the blockto see what happens.
The sprite shrinks a little bit! To make it grow again, click on the “change size by10” block back in the blocks menu. Great! Put that block underneath the “change sizeby negative 10” block, and click the stack to try it out.
The sprite doesn’t look like it did anything! It’s changing sizes too quickly for youto see. Make the sprite wait a little bit before it switches back to its normal sizeusing a “wait” block. This example uses a wait value of 3 seconds. Use any value thatworks for your project. Click on that block stack to see the sprite shrink, wait, thengrow again. Next, add an “if” statement around thisstack. Add a “touching” block from the “sensing” menu to the “if” block condition,and select “power up” from the drop down menu. Add the entire stack to the “forever”loop, below the other “if” block. Then, click the flag to test it out.
The sprite shrinks when it touches the power up, but there’s one problem. You can’tcontrol the sprite when it’s shrinking! The “go to” block and the shrinking blocksaren’t running at the same time. To fix this, add another block stack beginning with“when flag clicked” and a “forever” block. Move the “if” statement stack fromthe old “forever” loop to the new “forever” loop.
Test the code again. Great! your power up works!
Lastly, the power up sprite should appear less frequently. Power ups are rare treats!
Select the power up sprite, and place higher numbers in the “wait, pick random” block.
This example uses “pick random 5 to 10” seconds, but tweak these values until youare happy with your game. Here’s the gameplan!
Add a power up sprite. Make the sprite move across the stage by copyingthe code from the obstacle sprite. Make the racer shrink when it touches thepower up sprite by using the “change size by,” “wait,” “if then,” and “touching”blocks. Adjust how often a power up appears by tinkeringwith the values in the “pick random” block.
Choose an Add-On
Add a starting screen with instructions for your game.
Keep track of how long a racer stays alive and display the score.
Create a sprite that cheers on the racer.
Program your racer to do a cool trick at the press of a button.
Create a power up that shrinks the racer.
Add a sound that plays when the racer crashes into an obstacle.