Arduboy Course - Part II: Movement

Movement

• Create variables for the x and y position of our circle

• Check for button input and increase/decrease x and y accordingly

• Check that the position can’t go off-screen

• Draw a circle at the current x and y position!

• Can you change it so the circle moves faster?

• Can you make it so the circle’s radius can be changed with the A and B buttons?

Movement via Momentum + Gravity

• When we press a button we no longer change the x and y position directly

• Instead we change xMomentum and yMomentum

• Then we use xMomentumg and yMomentum to change the x and y position

• If the user doesn’t press LEFT_BUTTON or RIGHT_BUTTON, then xMomentum should decrease towards 0.0

• If the user presses A_BUTTON we add an upwards force to yMomentum to make them jump

• And we add gravity as a constant downward force that acts on yMomentum and pushes the player towards the ground

• Can you make it so the player can only jump when in contact with the floor?

🎓 Making it Frame-Rate-Independent

Arduboy tries its best to keep running at a stable frame-rate. So unless you’re in danger of dipping below the set framerate, you can ignore all this for simplicity’s sake. But be aware that in other game engines you usually run at variable frame-rates and very much have to account for that!

The previous example will behave different at different frame-rates. You can try this out by changing the setup function to this:

A low frame-rate like 20 brings it to a crawl, a high frame-rate like 120 puts it on steroids. But ideally we’d like it to behave the same no matter the frame-rate ends up being!

To achieve this we need to

• Calculate the deltaTime - the actual time that passed since the previous frame

• Set all our speed values in pixels per second and then multiply them by the deltaTime we calculated