UV Editor Slots, GLSL renders and Compositing

Can UV Editor’s Slots be used in Compositing?
Can i have two UV editor windows open, each showing different image (or Slot)?
How can GLSL render be used in Compositor in combination with Scene render (without using intermediate Save As and further loading back as image)?

Can’t have any of that as far as I know, except show two different images in the uv/image editor. Render result is one image, and could show render layer and composite versions of that by changing what layer is shown, but that’s about it.

Showing two different images, like render result and viewer node is possible, or whatever are available in the image datablock list.

JA12, thank you for answering.

I’ve run into these limitations while trying to do some illustrative material using GLSL render and Scene render as a composite source. To my surprise even separate Scenes did not allow to use GLSL render as a source without saving it as an image first. While it is just a couple of additional clicks for a static render, from a usability point of view this seems not expected, mildly put, especially now when viewport is being actively developed. I imagine i’d run into a lot more hurdles to use such compositing in some animation.
Being able to make use of Slots as a source for composite analysis (image difference e.g.) or artistic purposes could have been quicker without intermediate saves - i assume Slot image data is a low hanging fruit.

Likewise i am always wondering why i have to re-render same scene if i have changed any of Freestyle line style parameters: since Freestyle is a post render process, image is rendered and Freestyle has all the necessary Scene data to apply one line style, for a changed style same Scene data seems gone or irrelevant. That’s a different topic though.