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Newbie post. Problem with two samplers.

Subject: Newbie post. Problem with two samplers.
From: email@hidden
Date: Thu, 30 Jul 2009 16:38:12 +0100
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Hi Folks,
I'm very confused about how sampler coordinates work. I've read the manuals and a fair bit of theory. It's the practice I'm sticking on.

If anyone could offer any advice it would be much appreciated.

I'm writing a kernel app that will take change an image to black and white. The threshold is the image's average colour. Anything darker than average becomes black, and anything lighter than average becomes white.

In Quartz Composer I have the Area Average filter running fine. I can see the one pixel value that's generated and it looks good.

Here's the test code for this. For now "imageSampler" is ignored....

kernel vec4 threshold(sampler imageSampler, sampler averageSampler)
{
vec4 vec4Average = sample(averageSampler, samplerCoord(averageSampler));
return vec4Average;
}

Now, here's the funny thing. When I connect my video capture device input to the imageSampler parameter above, the billboard output goes black. Despite the fact I've made no coding changes.

I can only guess that it's something to do with coordinates. Perhaps samplerCoord no longer returns my 1 pixel average. I've tried replacing this with samplerTransform, etc. but no dice.

Any idea why this might be?

Many thanks,
Max

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