Clearing what is first drawn...

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312x312

Clearing what is first drawn...

in Programming Questions • 9 months ago

Hello.

Is there a way to clear/delete what is drawn at the very beginning when the sketch is run?

In other words, when this sketch is run, that rectangle at the top left corner is drawn due to the way in which the program runs, I believe. And I would like to know if there is a way to clear/delete that first object (rectangle).

The code is very simple to illustrate this question. I basically would want the Display Window to be in the background color and nothing drawn until the mouse is brought into the Window.

If there is a way around this, please advise! Thank you very much.

void setup(){
size(400,400);
background(100,0,0);
}
void draw(){
stroke(2);
fill(130, 100);
rectMode(CENTER);
rect(mouseX, mouseY, 50, 50);
}

Replies(4)

amnon.owed

Re: Clearing what is first drawn...

9 months ago

The problem is that mouseX and mouseY are 0 (zero) by default.

You can solve this problem by adding the following two lines at the end of setup:

mouseX = -1000;
mouseY = -1000;

312x312

Re: Clearing what is first drawn...

9 months ago

Thank you! This works great, but may I ask a few related questions?

• What is the reason behind assigning '-1000'?

I reduced the number to '-25' and it still worked. If it is set to '-25', you will see a corner of the rectangle at the top left corner of the Window. My first guess was it had something to do with the width and height of the rectangle...

• It seems that this solution works when the rectMode is set to 'CENTER'. Something funny happens when it is set to 'LEFT' or 'RIGHT'. A 50 x 50 rectangle is drawn and the subsequent rectangles are all drawn with a fixed top left corner at (50, 50). Would you explain this?

void setup(){
size(400,400);
background(100,0,0);
mouseX = -1000;
mouseY = -1000;
}
void draw(){
//background(100,0,0);
stroke(2);
fill(130, 100);
rectMode(RIGHT);
rect(mouseX, mouseY, 50, 50);
}

amnon.owed

Re: Clearing what is first drawn...

9 months ago

I am setting the mouseX and mouseY to a somewhat arbitrary off-screen number instead of the default 0. It can be any number and indeed the results will depend on the rectMode. As long as it's further away than any drawing. Choose a setting that works for your situation. Of course there are alternatives to this solution, for example by using an if statement that depends on frameCount, mouse position or a boolean.

With regard to your second question. LEFT and RIGHT are incorrect settings for rectMode, see the reference. The only reason they work is that LEFT, RIGHT, CENTER, CORNERS etc. are actually globally set integer variables in the Processing source code (aka 0, 1, 2, 3 etc.). So you are in fact setting a specific rectMode, but not RIGHT/LEFT (because they don't exist) but rather something like CORNERS. See the reference for CORNERS, it allows you to specify the corners of a rect. In your case you set one of these corners to 50, 50 which explains the fixed left corner.

312x312

Re: Clearing what is first drawn...

9 months ago

Thank you for the thorough explanation.

My apology on the rectMode! But you introduced me to some new ideas to try out.

Thanks again.

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