Trailing behind

Challenge 5 of 16

Maths works on these two as it did on frameNumber. Adding to mouseX puts the circle a fixed distance right of the pointer, so it trails beside it — wiggle your mouse and the gap never changes.

Work out the gap from a marker.

Your code JavaScript

Work out the gap from a marker.

Console print() output

0 / 60 frames · 400×400

Target

Yours

Results

Press Run to check your code

Penalties: none this run

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Lesson Follow the Mouse

Topic 1's numbers all came from the clock. These two come from you.

mouseX is how far across the pointer is, mouseY how far down — the same pair of numbers any shape takes for its position. So circle(mouseX, mouseY, 40); draws a circle wherever the pointer is, and that is a finished animation: no variable, no sum, nothing to set up.

They are values you read, never ones you set. You can take the number out of mouseX and use it, but you cannot put a number into it — the mouse decides, not your code.

Everything Course 2 and Topic 1 taught about sums works on them. mouseX + 80 is a fixed distance to the right of the pointer. 400 - mouseX is its mirror image, because the canvas is 400 across. And mouseX / 2 need not be a position at all — feed it to a size and the shape swells as you move right.

These challenges open in Try mode, and that is worth knowing about. Try mode means the picture is already live: the pointer is yours, so move it about and watch what happens. Nothing is being marked while you do, and changing the code updates the picture straight away — you never have to switch anything on.

Pressing Run is different. Then the pointer follows a path that was recorded for you, the same one every time, so your sketch and the target can be compared fairly — the dots on the playbar mark where it moves along that path.

So: play in Try mode until you understand what the challenge is asking, then press Run to be marked.