Jumping

At first jumping might appear simple.  All we need to do is set vertical speed when the player presses the Up arrow.

Why does -10 move upwards?

Problem

Our character can jump too well!  It should only be able to jump if it is standing on something at the start.  It should not be able to jump when it is already in the air.

We can fix this by adding in a block to test whether there is a collision 1 pixel below our character  (That means it is standing on something solid).

So now it can only jump if there is something solid beneath it.

What if it falls too fast?

Sometimes if our character falls a long way, gravity will cause it to get so fast that it might completely miss the collision with the platform event and go straight through it.  We can fix this by limiting the vertical speed.

In the Step event, add in:

So, as soon as the vertical speed gets bigger than 12, we just set it back to be 12.