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Oldskool feedback effect

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I really dont know how to do this effect. I've been really into oldskool democoding since a while, and i'm trying to make a demo with as much good effects as i can. Ive alot of dem now(water, fire, explosions,tunnel, plasma, lens, sphere mapping, a cool effect i made myself, PS look at my site there are a few of them http://members.lycos.nl/rubynl). Unfortunately I havent coded a single demo yet :*). I've googled for it, but feedback is a pretty shitty term to search for. I've seen the effect here: http://biskbart.free.fr/nouveau/progs/feedback.zip. The source(Qbasic) is with it, but I can't understand it. Does somebody know how to do this? Any link to a page where some explanation is, is also highly appreciated.

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this might be what you're after (or thereabouts):
http://sol.gfxile.net/gp/ch05.html

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Sorry, but that tutorial is using opengl or something and I program in pure qbasic. Thanks for your help, though, I really appreciate it you want to help me.
But, what I'm searching is a manner to do that feedback effect in pure code, like in the URL I posted in my first post. That is a great program, I think, and I want to make something like it.
Maybe someone can understand the post and explain it to me? This is really frustrating me coz I've been searching and thinking for ages...

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Quote:
Original post by RubyNL
Sorry, but that tutorial is using opengl or something and I program in pure qbasic. Thanks for your help, though, I really appreciate it you want to help me.
But, what I'm searching is a manner to do that feedback effect in pure code, like in the URL I posted in my first post. That is a great program, I think, and I want to make something like it.
Maybe someone can understand the post and explain it to me? This is really frustrating me coz I've been searching and thinking for ages...


In the link above, look at "05 - Blending a Bit ". That one explains how to blend and stretch the image buffer.

The effect part has nothing to do with OpenGL, although it could make things much faster.

The idea is simple:
1) Draw something into buffer1
2) Scale buffer1 by x% into buffer2
3) Blend buffer1 and buffer2 into buffer3
4) Copy buffer3 into buffer1
4) goto 1

Buffer here are the pixels that make up your image. Typically an array of RGB colors, so W*H*3 bytes.

And the blending part is demonstrated in the link. What you do, is you take pixels from the same location in each of buffers, and perform some function on them (average, min, max, ...), then store the result in third buffer.

This is also the reason why you store the pixels in an array - the pair-wise operation that becomes trivial, since you need to calculate the operation between elements at same offset in each of the array (buffer3 = (buffer1+buffer2)/2 - for example)

Obviously this is possible with no overhead and single buffer, but that's not the point here.

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