tx for u response Art ,
if i understand u correctly my code will be something like this ,i am using
glew .
(suppose my input texture where i want to find my maximum value is
(width,height) and i have a FrameBuffer class and a GL_Texture class, and a
shader.)
inputtexture=new GL_Texture(...width,height...)
n=2;
fbo=new FrameBuffer(...)
loop
{
outputexture=new GL_Texture(..width/n,height/n)
//activate fbo to render to texture
fbo->Bind();
//attach a outputexturetexture to render to it
fbo->AttachTexture(outputexture);
//setup viewport to size of outputetexture
glViewport(0, 0,width/n,height/n);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
glOrtho (0, (GLdouble) ,width/n, 0,height/n, -30, 30);
glClearColor(0,0,0,0);
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
//activate inputtexture and run shader
inputtexture->Activate(GL_TEXTURE0);
shader->begin();
//pass inputtexture to shader
shader->setUniform1i("texture0",0);
//Here i render a Rectangle at width/n and height/n
//disable shader and fbo
shader->end();
fbo->Disable();
//go to next step of reducing inputtexture
n*=2;
//copy outputetexture to inputtexture for next iteration :
inputtexture=outputexture
inputtexture=GetCopy(outputexture);
delete outputexture;
}//end loop
and in the fragment shader all i have to do is : each pixel shader will
calulate a maximum for 4 neighberhood texels of the input texture ?
is it correct ?
thx in advance
> Message: 5
> Date: Tue, 5 Aug 2008 17:09:45 +0000 (GMT)
> From: Art Tevs <[EMAIL PROTECTED]>
> Subject: Re: [osg-users] using shaders to find fthe maximum value in a
> texture
> To: OpenSceneGraph Users <[email protected]>
> Message-ID: <[EMAIL PROTECTED]>
> Content-Type: text/plain; charset=utf-8
>
> Do you need the maximum value over all texture elements?
> If yes, then you just have to compute a mipmap with max as combining
> operation. In the last level, where only one pixel left, you will get the
> maximum value.
> It is pretty straight forward to implement such an algorithm.
>
> Either any GPGPU approach can help you, or if you use osg, then take a look
> into osgPPU's hdr example.
>
> Best regards,
> Art
>
>
> --- Abdallah Deeb <[EMAIL PROTECTED]> schrieb am Di, 5.8.2008:
>
> > Von: Abdallah Deeb <[EMAIL PROTECTED]>
> > Betreff: [osg-users] using shaders to find fthe maximum value in a texture
> > An: [email protected]
> > Datum: Dienstag, 5. August 2008, 16:56
> > Hello,
> > i am new to glsl , i have a probleme ( it seems that it is
> > fondamental problem in shaders)
> > in order to calculate the maximum/minumum value in a
> > texture passed to fragment shader ,
> > it seems that there is as special architecture to implement
> > to resolve this probleme .
> > i passed a days searching on the net to solve this problem
> > but no one discuss this probleme and how to calculate a
> > maximum or minimum in a texture or vector norm ... i heard
> > something called vector reduce in shaders.. but i have no
> > clear idea about it .
> >
> > so in resume my question is how can i create a fragment
> > shader that can calculate (a maximum value for ex) in a
> > texture passed to it ,
> >
> > if anyone can help me plz , i really need an
> > implementation or a reference docs..
> > thx in advance .
> >
> >
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