Hi Julien,
you might be lucky if your output pixel does not depend on any input
neighbours. Imagine all output fragment shader progs being executed in
parallel with no fixed order. If an output pixel depends on input
neighbours, the input values might be overwritten before they are read.
I also tried this when I started osgpingpong (try it) and you get weird
results.
jp
Julien Valentin wrote:
I Have used a copy of unchanged pixels and it works,
but I have still a question:
I try to remove the pinponging by giving the 2 passes same textures as
input and output... ( new renderPass(texture[0],texture[0]))
And it works perfectly?!!! Performances are the same and i can use discard
Can someone can give me clues about why is it working as everywhere on
the net advise not to use a read/write texture in shader???
Hi,
try copying the input texture value to the output instead of using
discard.
jp
Julien Valentin wrote:
> Hello all,
> I'm playing with the osg gameoflife example in order to implement a
> FastIterativeMethod using the pingpong textures and a FBO already
in the
> example.
> This iterative method is looping over several GPU loops (a pixel
> shader) until it converges ( all pixels are set).
> Pixel shader seems like it:
> main(){
> if (need to update current pixel)
> gl_FragColor=updatedcolor;
> else gl_FragColor=oldcolor;;
>
> }
> It work fine but there's no convergence test in order to stop
looping in
> the shader....
> For the purpose of convergence test I would like to use an occulsion
> query that return the number of pixel setted in a loop (not
discarded).
> For this I modify my shader:
> main(){
> if (need to update current pixel)
> gl_FragColor=updatedcolor;
> else discard;
>
> }
> So It discard fragment that dont need to be setted again with the
same value
> Now each pixel would update when it need otherwise it is would
discard
> itself.
>
> But with this code the result on my textured quad s don't stop
flicking
> between correct color and a checkboard ..:(
>
> Do you know where the problem is?
> It seems to be like osg is not calling the two pingpong passes
> alternately...
>
> NB:To sum up, The only change I made from the osg gameOfLife
example is
> the shader where i introduces a discard branch...
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