2. Create a Scrolling Backdrop

In this video, you'll program the background sprites to scroll.

In the starter project, three different cave sprites act as the background.

The first cave sprite is red, the second is blue, and the third is green.

In this example, one cave sprite closely follows the next forming what looks like a continuous scrolling background.

In the starter project, there is code that's been added to each cave sprite.

This code starts the first cave at x times 480, the second at two times 480, and the third at three times 480.

The code also contains a variable, distance traveled.

Each time these loops run, each sprite goes to a new position based on the value of distance traveled.

You can imagine how this might look outside of the Scratch Viewer.

Imagine you have three sprites that are all 480 pixels wide.

You need to set the first to start with an x value of 480, the second to start with an x value of two times 480, or 960, and the third to start at an x value of three times 480, or 1140.

The distance traveled variable increases as the sprite moves, advancing the background sprites.

When distance traveled equals zero, the sprites stay at the current position.

When distance traveled equals one, the sprites all move to the left one step.

When distance traveled equals two, the sprites all move to the left another step and so on until the backdrop has scrolled all the way across the stage.

To make the backdrop scroll, program the distance traveled variable to increase throughout the game.

Click the player sprite and drag out a change distance traveled block.

Add a when flag clicked box above this.

Click the flag a few times to test this code.

Each time the program runs, the value of distance traveled goes up by one and the caves move one step to the left.

If you try a higher value, like 50, you can scroll through all the caves just by running the code a few times.

Next, increase the value of distance traveled repeatedly.

Add a forever loop from the control menu to the change block.

Click the flag to test.

Whoa, that was fast.

If you click the flag to test again, the program won't run.

The distance traveled variable holds a value.

When you start the game, the variable is still holding the value of the distance traveled from the last game.

To fix this bug, add a set distance traveled to zero block under the when flag clicked block to reset the game.

Click the flag to test.

Great, the distance traveled variable starts at zero, then increases.

Tinker with the value in the change distance traveled block until the sprites scroll across the screen at a pace you like.

Now it's your turn.

Add a change distance traveled by block and a green flag event, a forever loop, and a set distance traveled to block.

Program the distance traveled variable to increase throughout the game.

Set the distance traveled to zero when the flag is clicked.

In the next video, you'll control the rising and falling of the player sprite with an if-else statement.