Down the screen

Challenge 1 of 16

Across was only ever the first argument. Feed a number to the second one instead and the shape falls, because y counts downward from the top of the window. The pattern is identical.

Set how fast it falls.

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Set how fast it falls.

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Lesson Down and Across

Which way is forward.

x counts across from the left, y counts downward from the top. That second one catches everybody: adding to y sinks a shape, and taking away from it makes it climb. A negative speed is not "backwards" — it is whichever direction that axis counts from.

Two numbers, no conversation.

x = x + speedX; and y = y + speedY; are two separate instructions, and neither knows the other exists. Equal steps happen to draw a 45 degree line; make the across step three times the down step and you get a long shallow drift instead. The angle is just the ratio of the two numbers — challenges 6 and 7 are the same code with the numbers swapped, and they look nothing alike.

Reading two at once.

The readout along the bottom now shows both numbers, on the target as well as on yours. Challenge 13 gives you nothing else: drag to a frame, read what each number has reached, and work backwards to the steps.