Thanks for your help.
But the solution that you gave me it's not really what I want to do. The
simple example i gave you it's just to explain what kind of result I need.
Actually I'm trying to implement a Dual Depth Peeling based on the Nvidia
Paper and it use this kind of blending. For example in my shader if I do
that:
int i=0;
void main()
{
if(i=0)
{
gl_FragData[0 = vec4(1.0,0.0,0.0,1.0);
i=1;
return;
}
gl_FragData[0] = vec4(0.0,1.0,0.0,1.0);
}
I would like have yellow in my texture for now I have green. Here again it's
just an example, but that's why i would like to use a blend equation, it's
the same problem as the other example I gave you I would like do a MAX
blending between the value previously in the texture and the new value.
Have you an idea how to do that?
2010/1/7 J.P. Delport <[email protected]>
> Hi Clement,
>
>
> clement vidal wrote:
>
>> Hi JP
>>
>> For now I Initialize a texture with the value A, in the shader I put the
>> value B and I would like to have a the end in the texture the max blending
>> between the value A and B.
>>
>> Lets do an example:
>>
>> I create an texture Tex initialized with color red (1,0,0,1)
>>
>> I attach my texture to a camera
>> Camera->attach(osg::Camera::COLOR_BUFFER0, Tex);
>>
>> I use a shader witch do this treatment: gl_FragData[0] =
>> vec4(0.0,1.0,0.0,1.0);
>>
>> And I would like have a yellow (1.0,1.0,0.0,1.0) texture at the end of the
>> treatment.
>>
>> For now using an osg::BlendEquation with RGBA_MAX blending, I have if I
>> define a clearColor to my camera the blending between this clearColor and
>> the color use in the shader. I think this is normal because the
>> blendEquation define how the blending is doing between the color previously
>> in the frame buffer and the added color. But it's not what i want I would
>> like to have the blending between the color previously in the texture and
>> the added color.
>>
>
> OK I think I understand better now. To use your texture as input (in order
> to kind of make it the background (as you have working with clearcolour))
> you will have to map it onto a quad (screen/camera projection aligned) [1].
> Then you make your camera look at this quad and the fragment shader would
> then blend with the texture in the frame buffer. Reading from and writing to
> the same texture can sometimes give problems, so you might have to make a
> copy for the output (ping-pong, see osggameoflife).
>
> I'm also not sure why you want to use blending, do you have some special
> algorithm that needs it? If you have an initial texture with input values,
> you can just sample it in your shader and modify the value yourself (based
> on maths, input uniforms or other textures) and put it into the final
> texture.
>
> [1] Attachments to the camera are outputs, textures bound to geometry are
> used as inputs for RTT.
>
> cheers
> jp
>
>
>
>
>> Thanks for your help
>>
>> Clement
>>
>> 2010/1/7 J.P. Delport <[email protected] <mailto:[email protected]
>> >>
>>
>>
>> Hi Clement,
>>
>> could you explain a bit more what you expect and what you are
>> getting? Do you want to blend between the different textures (AFAIK
>> you cannot do this unless you do another pass)? Are you expecting
>> max, but getting average?
>>
>> jp
>>
>> clement vidal wrote:
>>
>>
>> Hi,
>>
>> I have a problem with BlendEquations and shaders. That is the
>> situation:
>>
>> I attach several textures to my camera using COLOR_BUFFER0,
>> COLOR_BUFFER1, ...
>> I use a shader to make the rendering into this textures.
>>
>> There is some values in this textures and i would like to use a
>> max blending between the value wich are already in and the
>> values i affect in the shader.
>>
>> When I define an osg::BlendEquation with RGBA_MAX blending, i
>> have the blend result between the value in the frame buffer
>> (background color or ClearColor ) and the value in the shader.
>>
>> What I do wrong? Somebody have a idea?
>>
>> Thanks for helping
>>
>>
>>
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