Once you have downloaded the project file you will notice that the script is short! There are really just two main behaviours we want to program and they are: Running and Jumping. Let's begin:
Step 1: Program Scratch Cat to run left and rightLet's start with a new program. We have the default Scratch Cat and a blank Stage. We paint a black strip on Stage with the Paint Editor. That's our floor.
|Code to move Scratch Cat left and right with the arrow keys|
Run the script now and you should be able to move the cat left and right with the arrow keys, as if it is skating. That is not what we want. We want it to look like it is running. We will fix this later after we have programmed it to jump.
Currently, notice that Scratch Cat stops as soon as it reaches the left or right edge of the stage. We will add in a script to "roll up" the screen such that when Scratch cat reaches the right edge it continues to the left edge and vice versa:
|Makes sure that Scratch Cats "rolls over" from edge to edge|
Now, on to the next step:
Step 2: Program Scratch Cat to JumpJumping essentially involves falling. Think about it. As soon as our feet leave the ground, we are already acted upon by gravity. The reason we are able to leave the ground is because the force we muster in our jump is greater than that of gravity. Nevertheless, due to gravity, our velocity decreases all the time as soon as we jump. Here is how we will translate this in Scratch: We add in the code for falling first. Refer to the tutorial on programming a falling object in Scratch for a better understanding of this script.
|Blocks added into the script above to simulate fall|
|Blocks for jumping|
The only thing missing now are the running legs. We will do this by alternating the costumes. Note that we only want Scratch to move its legs while running on the ground and not while its jumping in the air, so we slip in controls for this in the if y position < -80 block (i.e. if it is on the ground):
|Blocks to change costumes, giving the impressing of running|
|Final script to make Scratch Cat run and jump with the keyboard|
Note: if you have downloaded my project you will notice that I have used variables to store my values. If "variables" sound alien, you may go without them for now. We will have a tutorial about them soon.