Start it further along

Challenge 2 of 12

frameNumber is an ordinary number, so Course 2's sums all work on it. Adding shifts the whole journey: the circle still creeps a pixel per frame, but it no longer starts at the left edge.

Step both pictures to frame 1 and read where the target starts.

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Step both pictures to frame 1 and read where the target starts.

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0 / 60 frames · 400×400

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Penalties: none this run

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Lesson Every Frame

Every sketch you have written has had its drawing inside everyFrame, and the name is the whole truth: that block runs again for every frame you see, about ten to thirty times a second.

frameNumber counts those runs. On the first frame it is 1, on the second 2, and so on. It appears at the bottom of every picture in this topic so you can watch it climb, and the ‹ › arrows under the picture step one frame at a time so you can take it slowly.

The important thing is that frameNumber is an ordinary number. Everything Course 2 taught about sums works on it, and each sum does something different to the motion:

frameNumber + 150 starts the journey further along.
frameNumber * 6 makes each frame count for more, so it moves faster.
frameNumber / 2 makes each frame count for less, so it moves slower.
380 - frameNumber counts down, so it goes the other way. Order matters here, as it did with any take-away: frameNumber - 380 is not the same thing and sends the shape straight off the left.

And it does not have to be a position. Feed it to a size and the shape grows; feed it to two different arguments and it does two jobs at once.

There is a second way to watch, too. Run grades sixty frames and stops; the Try button just runs your sketch, with no marking and no frame limit, until you press it again. Use it whenever you want to watch something for longer than a run allows.

One thing frameNumber cannot do: stop, turn round, or go home. It only ever counts up. That is what the next few topics fix, by giving you a number of your own that you decide how to change.