If I pass vertices to a shader between -1 and 1, with 0 being the middle of the screen.

would I be able to use those values without any modifications?

Yes

Those are the limits in the Normalized Device Coordinates system (NDC)

If you also want UV coordinates for this, simply do:

out_texcoord = (in_vertex + vec2(1.0)) * 0.5;

note that this is only for a fullscreen quad

for anything else you will want to provide UVs as well

Yes, but you must make sure that the w component of the vertex position is 1, because the perspective divide will still occur after the vertex shader.

Thank you :)

What are the UV quads relative to?
If I provided a quad's verticies between -1 and 1 couldn't I use them again for the UV if it's relative to the screen

or -1 and 1 if it's relative to the quad.

Thank you

What are the UV quads relative to?
If I provided a quad's verticies between -1 and 1 couldn't I use them again for the UV if it's relative to the screen

or -1 and 1 if it's relative to the quad.

UVs are texture coordinates, between 0 and 1, unless the texture repeats, always

Of course there are lots of variations on how people specify these coordinates due to eg. texture atlasing.

But, what I did in my example was simply scaling the vertex coordinates [-1, 1] to [0, 1] so that you could re-use the vertex coordinates for a fullscreen quad. Those UVs represent the entire texture.

To answer your question - yes, but you still need to rescale the UVs to match the [0, 1] scale of texture coordinates.

Great I see what you mean by a fullscreen quad, because the math would break otherwise.

That was the confusion.