thank you wretchedSid.

Now that I understand UV coordinates are actually 0,1, I can see why now the following snippet causes only half the screen to be post processed:

if (texCoord.y >= .5) // postprocess only the lower half of the image
{
...code
}


So the pixel shader , in a sense, applies its effect over every pixel, in this case every pixel of the render target/render buffer quad.

Why is it called a fragment? A pixel shader runs its code for every single pixel, are these the "fragments" that make the whole surface?

So knowing that UVs are 0,1, how would I be able to find the color of an arbitrary pixel within the texture? I want to find the rgb values of the pixel thats x=32 and y=245 for example, how would I do this? vecViewPort?