Over the ground

Challenge 14 of 16

A scene is the same maths with something to look at. The ball travels right and sinks as it goes, so it is almost at the grass by the end without ever touching it.

Set the across speed to 7 and the down speed to 5.

Your code JavaScript

Set the across speed to 7 and the down speed to 5.

Console print() output

0 / 45 frames · 400×400

Target

Yours

Results

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Penalties: none this run

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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.