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Index › Programming Questions & Help › Syntax Questions › Trails behind boids

Buckeye YaBB Newbies Offline Posts: 2	Trails behind boids? Nov 27th, 2009, 2:00pm   Hi I've been looking at the Daniel Shiffman flocking code, and wondering if there is a way to put trails behind each object to map their movements? I'm sure this has been done before, and have to confess my ignorance- as an architecture student I am completely new to all of this! Any help is much appreciated.

Cedric YaBB Moderator Offline Posts: 1838	Re: Trails behind boids? Reply #1 - Nov 27th, 2009, 2:42pm   the easiest way if you dont want to add anything else is to call fill(0,40); rect(0,0,width,height); instead of background(0); this always fills the screen with a semitransparent rect. if that doesnt help you you need to create an array store the previous positions and draw some trails behind your boids.
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PhiLho  YaBB Moderator Offline Posts: 4190 Near Paris (France)	Re: Trails behind boids? Reply #2 - Nov 28th, 2009, 2:31am   background() accepts an alpha value. It doesn't work?

blindfish God Member Offline Posts: 793	Re: Trails behind boids? Reply #3 - Nov 28th, 2009, 2:41am   PhiLho  wrote on Nov 28th, 2009, 2:31am: background() accepts an alpha value. It doesn't work No.  The sketch runs but the alpha is ignored.  I think that's worth some investigation and getting the reference updated as it seems to be a recurring problem people run into...
	Where is the what if the what is in why?

PhiLho  YaBB Moderator Offline Posts: 4190 Near Paris (France)

Re: Trails behind boids? Reply #4 - Nov 28th, 2009, 8:27am   Ah, right! Actually, it is documented, I scanned the page too fast: "It is not possible to use transparency (alpha) in background colors with the main drawing surface, however they will work properly with createGraphics." Which makes sense: actually background() isn't strictly equals to a call to rect() but it just fills the area with the given color. And a background transparency on the main sketch area makes thus little sense (what to show thru?).