A dot where you clicked

Challenge 3 of 16

The two numbers can go into variables of your own with any names you like, and be drawn later. Here markX and markY hold the last click and a small dot is drawn there, beside a ball that never moves.

Set the two lines that fill the marks.

Your code JavaScript

Set the two lines that fill the marks.

Console print() output

0 / 48 frames · 400×400

Target

Yours

Yours over Target — ghosted shapes are in the target but missing from yours

Results

Press Run to check your code

Penalties: none this run

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Lesson Where Did I Click?

A click happens somewhere. The sketch can find out where, because two values are waiting to be read:

mouseX is how far across the click was
mouseY is how far down it was

Both are ordinary numbers, so they can go anywhere a number can go.

function whenMouseClicked(){
x = mouseX;
y = mouseY;
}

That is the whole idea. Read them inside the handler, keep them in your own variables, and let everyFrame draw from those variables as it always has.

They are numbers, which means you can do arithmetic on them. All of these are fine:

x = mouseX + 60;
y = mouseY - 90;
x = width - mouseX;
howBig = mouseY;

The last one is worth a second look. mouseY is a number somewhere between 0 and 400, and so is a size, so a click low down can make a big shape and a click high up a small one. Nothing says the click has to move anything.

There is one thing to be careful about, and it catches people. When two lines both run on the same click, the order matters:

oldX = x;
x = mouseX;

Keep the old value first, then take the new one. Write those two the other way round and the old value is gone before you saved it, so both variables end up holding the same number and the two shapes land on top of each other.

The readout along the bottom of every picture in this course shows mouseX and mouseY the whole time, so you can always check a number you have worked out against the one it came from. And the little dot on the scrub bar marks the frame each scripted click happens on — step across it one frame at a time.

In the last challenge there are no clicks at all. That is because mouseX can be read from inside everyFrame too, and there it means something slightly different: where the mouse is right now. Following the mouse without clicking is the next topic.