Witty.ca - Graham's Professional Archives

For those of you who've never used Scratch (a free programming tool from MIT), try my tutorials 1,2 & 3.

Never heard of the Frogger video game?
Try here (wikipedia) or here (Konami).
(Or, just do a search for "Frogger".)

In this unit of study, we'll be building our own Frogger-style video game.

In this unit, we'll cover:

• positive & negative numbers
• X and Y coordinates
• loops and conditions
• variables and "broadcasts"
• object-oriented programming
• input devices (e.g. keyboard)
• event sequences
• ... and more

We are going to build our Frogger video game will only accept input from the arrow keys on the keyboard. 

So, go ahead and change that cat into a frog.  
But then what?

We need to build a block that:
    if 
        a key is pressed
                                       then move the frog in only that direction.

And so, that's exactly what we build.  
Make it look like this.

Now, you have the building blocks,
so change the settings that:
    if 
        the right arrow key is pressed
                                       then move the frog 3 steps to the right.

In Script 3e, we learned how to go down.  
Use that knowledge to figure out how to also go left.

Now, put it all together, so your script can sense and react to:
   up,   down,   left,   and   right.


Test this out!     Does it work?

Next up, making a background!

Select the Stage object.

      Select the Backgrounds tab.
 
               Click the Edit button to modify the costume.

There are two choices below. 
They both show how to construct the highway image for the stage (background).

What to do -- click image for animated GIF  -->

How to do it  -- below on YouTube     .

Trust me, this will keep everything nice and orderly!


NEAT TRICK:
Rather than making hundreds of cars, we're going to re-use our car so that (for now) only one car travels in each lane.

To do this, we're going to make our car drive across the video game screen, and then "teleport" back to the beginning of the lane.

Watch this video to get the idea.

The second car takes some thinking.  
Check out the video below.

Object-oriented programming is great because everything is an object.  If you want another, just "duplicate" it.


What did you say?

You tried it, but it's all messed up?

Ah ha!  The dreaded copy-and-paste error rears its ugly head!


Watch this video to see where to make changes.

Yes, you're completely right.  After showing us how to do the second car, there is absolutely no need to make a video showing how to create a third car.

So go ahead.  It'll be easy....     ...right?

Ummmm.  Teacher!  Why is my car smashing into the wall? ... over and over and over again?


Well, that's not really "bashing".  No, it's more like a "jiggly dance", and the car is doing exactly what you've programmed it to do.

Maybe you should watch this video to discover the simple solutions to fix your problem.

Sadly, in a video game called "Frogger", the whole point is to see how long the frog lasts before it dies.

Thankfully, no actual real live frogs were harmed in the making of this game.


But today, you get to learn how to kill those pesky virtual frogs.  You need to start by thinking like the blue car.   

Once you can get into the mind of the blue car, everything else is easy.

Now that you've killed the frog, it's time to bring the poor guy (or girl) back to life!

So, here's a list of all the things that need to happen between the death and re-life of the frog.

In ALL cars:

• Dead frog message sent (variable)

In the frogger:

• Dead frog message received (variable)
• Frog stops moving
• Frog displays a message (looks = words)
• Frog makes dying sound
• Frog goes back to start (try glide!)
• Frog comes back to life (variable)