hi Glen,
Kudos for the shift >> 1 operation, knew that was a faster operand.
However, this code is still now working, now it simply doesn't change
anything...
:(
var val:uint = getPixel32(x,y);
var a:uint = (val >> 24) & 0xff;
var rgb:uint = val & 0xffffff;
a = a >> 1;
var newval:uint = (a << 32) | rgb;
setPixel32(x,y,newval);
I also tried changing it to say:
...
var rgb:uint = val & 0x00ffffff;
a = a >> 1;
var newval:uint = (a << 24) | rgb;
...
since I thought that was an error maybe, but that also doesn't influence
the alpha of the pixel...
:(
Out of desperation I also tried:
var a:uint = val & 0xff000000;
var rgb:uint = val & 0x00fffff;
a = a >> 1;
var newval:uint = a | rgb;
and
var a:uint = val & 0xff000000;
var rgb:uint = val & 0x00fffff;
a = a >> 1;
var newval:uint = (a << 24) | rgb;
:(
sniff...
Setting alpha for the whole MC is not an option for what I am doing. I'm
trying to create trails behind things that are moving by having a
video-burn like effect; by operating on the pixel level. At the moment I
am using code from 'Adventures in AS', but once i have it working I'll
encapsulate it and use it in a different project.
The original source is:
http://flashcoding.blogspot.com/2008/03/small-starfield-with-bluring-effect.html
And my current draft-code modification is:
package
{
import flash.events.*;
import flash.display.*;
import flash.display.Bitmap;
import flash.display.BitmapData;
import flash.geom.Rectangle;
public class Starfield
{
var mc:MovieClip =new MovieClip();
var screendata:BitmapData;
var stars:Array=new Array();
var antal:Number=500;
public function Starfield(timeline)
{
screendata=new BitmapData(320,240,false,0x00000000);
var screen:Bitmap=new Bitmap(screendata);
mc.addChild(screen);
for (var i:int=0;i<antal;i++)
{
InitStar(i);
}
mc.addEventListener(Event.ENTER_FRAME,this.render);
timeline.addChild(mc);
}
private function MoveStar(index:int)
{
if (stars[index][0]<-160 || stars[index][0]>160 ||
stars[index][1]<-120 || stars[index][1]>120)
{
InitStar(index);
}
else
{
stars[index][0]=
stars[index][0]*stars[index][2];
stars[index][1]=
stars[index][1]*stars[index][2];
}
}
private function InitStar(index:int)
{
stars[index]=[Number(((Math.random()*10)-5)),Number(((Math.random()*10)-5)),Number((Math.random()/10)+1)];
}
private function render(e:Event):void
{
for(var x:int=0;x<320;x++)
{
for(var y:int=0;y<240;y++)
{
var val:uint = screendata.getPixel32
(x,y);
var a:uint = (val >> 24) & 0xff;
var rgb:uint = val & 0xffffff;
a = a >> 1;
var newval:uint = (a << 24) | rgb;
screendata.setPixel32(x,y,newval);
}
}
for(var i:int=0;i<antal;i++)
{
MoveStar(i);
screendata.setPixel(stars[i][0]+160,stars[i][1]+120,0xFFFFFF);
}
}
}
}
Regards,
Sebastian.
Glen Pike wrote:
Hi,
I think you need to shift by 24 for alpha, you also need to shift
then mask the value. RGB is just the bottom three bytes masked and
shifting by 1 rather than divide by 2 may be faster, but google for the
speed comparisons in AS3 - I think John Grden may have blogged this:
var a:uint = (val >> 24) & 0xff;
var rgb:uint = val & 0xffffff;
a = a >> 1;
var newval:uint = (a << 32) | rgb;
It would be a good learning exercise to do your own equations for
manipulating pixel stuff, but have a look at Mario Klingemann's blog -
quasimondo.com - for tips and tricks with images as he is one of the
best people at manipulating bitmaps in Flash so he may have some nice
examples to stimulate you. For simpler manipulation have a google.
Also, if you are just setting the alpha to 50% for the whole bitmap, it
may be quicker to do this on the MovieClip because FlashPlayer might be
optimising composition somehow, but I understand this may just be an
example.
HTH
Glen
sebastian wrote:
Thanks Glen and Andrew,
Thanks for your fast help,
Tried to use this code [below] but it makes my pixels yellow instead
of 50% alpha on each pass... any ideas why?
Is there any good tutorial on working with bit operations and bit
logic? Would make it easier for me to trouble shoot/make my own
equations.
:)
Thanks!
Seb.
Andrew Murphy wrote:
I'm not sure of this, but: After you grab "val" you could bitshift
out the
alpha channel ("a"), subtract that from the original argb value to
remove
the alpha channel. Manipulate "a" and bitshift it back up again before
adding it to the rgb value to give you a new argb.
var a:uint = val >> 32 & 0xff;
var rgb:uint = val - (a << 32);
a = a / 2;
var newval:uint = rgb + (a << 32);
--------------------------------
Andrew Murphy
Interactive Media Specialist
[EMAIL PROTECTED]
Delvinia
214 King Street West, Suite 214 Toronto Canada M5H 3S6
P 416.364.1455 ext. 232 F 416.364.9830 W www.delvinia.com
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-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
sebastian
Sent: Monday, October 06, 2008 3:18 PM
To: Flash Coders List
Subject: [Flashcoders] working with getPixel32 and setPixel32,
hi folks,
can any one shed some light to me on the setpixel32 and getpixel32?
I'd like to be able to affect just one of the 4 components: A R G or
B independently of another.
Essentially, read the current ARGB using getPixel32 and then
manipulate just one part of it, in my case, halve the current "A"
value of the ARGB and then re-assign it back to the bitmap.
//1: grab the HEX value for the current coordinate:
var val:uint = getPixel32(x,y);
//2: manipulate the HEX value of just 1 of the 4 parts, in my case
the A of the ARGB:
????
//3: re-assign it back to the display:
setPixel32(x,y,val);
Thanks for your help!
Sebastian.
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