The Keyboard

Eight chapters of things moving on their own. Now you get to interfere.

update has always taken a second argument you've been ignoring:

keys is a dictionary telling you what is held down right now:

Two keys, that's all there is. It's enough — some of the most-played games ever made use one button.

Height, not row

Games measure a character's height upward from the ground, not downward from the top of the screen. From here on:

Bigger y now means higher, which is the opposite of everything you did in Chapters 2 to 8. It reads better once you're jumping — "y is how high I am" is easier to hold in your head than "y is how far down the screen I am".

Your grid still counts rows downward, so convert when you draw:

At y = 0 that's GROUND — standing on the ground line. At y = 5 it's five rows higher up the picture. One line, in draw, and the rest of your code gets to think in heights.

Gravity, upside down

Because y now means height, gravity subtracts:

A jump sets vy to a positive number. Gravity eats one off it every frame, so vy goes 3, 2, 1, 0, -1, -2 — the hero rises, slows, hangs for a moment, and comes back down. That hang at the top is not something you code. It's what happens when a number passes through zero.

Note the order here: move first, then apply gravity. Chapter 4 did it the other way. Both work — this is the order Coin Quest uses, so it's the one we'll use from now on.

Only jump when you can

Without and state["y"] == 0, holding space lets the hero fly. Sometimes that's the game you want. Usually it isn't.