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Topic: screen/pixels vs. alpha channels (Read 277 times) |
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elout
 
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screen/pixels vs. alpha channels
« on: Jan 25th, 2004, 8:04pm » |
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I started today to do a 2004 remake of my old 'zab0' applet. This time in processing & the first thing to do was; doing 'my draw the screen onto the screen trick', with a little different offset...
And I just noticed, the huge difference between
doing;
my_imagebuffer.pixels=pixels;
or;
System.arraycopy(pixels, 0, my_imagebuffer.pixels, 0, width*height);
I guess it has to do somehow with the alpha channels.
Any insight in this one?
Code:
// zabnulvier v.001 - elout de kok - www.xs4all.nl/~elout/
// compiled in processing v.0067 www.processing.org
// 25 jan 2004
BImage my_imagebuffer;
int midx,midy;
int noisefactor=30; // make this bigger --> for more noise fun
void setup()
{
size(600, 300);
my_imagebuffer = new BImage(width, height);
midx=width/2;
midy=height/2;
}
void loop()
{
//draw something
stroke(random(255),random(255),random(255),90);
fill(random(255),random(255),random(255),90);
quad(midx-10,0, midx+10,0, midx+10,height, midx-10,height);
quad(0,midy-10, width,midy-10, width,midy+10, 0,midy+10);
//now copy the screen to my screenbuffer -- 2 options;
my_imagebuffer.pixels=pixels;
//System.arraycopy(pixels, 0, my_imagebuffer.pixels, 0, width*height);
// arraycopy -- source,start, destiny,start , size
//my old trick; draw the same screen onto the same screen
// with a slighty different offset
image(my_imagebuffer, random(noisefactor)-noisefactor/2,random(noisefactor)-noisefactor/2 );
}
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my favourites until now;
using
- my_imagebuffer.pixels=pixels;
and setting noise factor around 100
- int noisefactor=100;
online sample..
http://www.xs4all.nl/~elout/proce55ing/zabnulvier/
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| « Last Edit: Jan 26th, 2004, 2:55am by elout » |
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benelek
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Re: screen/pixels vs. alpha channels
« Reply #1 on: Jan 27th, 2004, 1:23am » |
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Hi elout,
from a quick look at your code, i don't think it's related to alpha. there's a subtle difference between using the equals sign and using the copy method when using arrays.
try the following:
Code:int[] array1 = new int[100];
int[] array2 = new int[200];
//System.arraycopy(array2,0,array1,0,array1.length);
//array1=array2;
println(array1.length); |
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when you use the equals sign, array1 actually becomes a reference to array2, and therefore has the same length as array2. if you modify array2 afterwards, array1 would automatically feel those changes.
however, when you use arraycopy(), array1 simply becomes a copy of array2, with all its values. however, it is still an independant array and is not updated until you do it yourself.
with regards to your sketch, because the pixel array of my_imagebuffer is a reference to pixels, when you write to pixels - by using image(my_imagebuffer) - the changes are made immediately to my_imagebuffer so there's a bit more of a feedback loop than you had originally.
~jacob
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elout
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Re: screen/pixels vs. alpha channels
« Reply #2 on: Jan 29th, 2004, 5:39pm » |
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Thanks, I understand now,
If I do; my_imagebuffer.pixels=pixels;
everytime 'pixels' changes;
the array my_imagebuffer[] will change as well.
Anyway I updated my 'zabzero 2004' edition.
http://www.xs4all.nl/~elout/proce55ing/zabnulvier/
Best played with some drum&bass in the background,
and will add some extra animations in the near future.
As a VJ I know, if you make the animation faster than the music, the visuals will look like they sync with the music.
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