This post became VERY interesting thanks to all your different approaches and solutions! :)
Sorry for this long post, I hope that some of you may find this interesting:
Since I'm not a programmer, but I am a professional animator (my day job) and have years of experience with post production, my simple-brain wanted to try the same way I use when I work on a post production stage for a video.
It's called "color grading" and it can get much more complex than what I tried here, but I think this will make my original goal (2 points gradient covers the layout) a bit more interesting with my approach joins to the party.
Basically in video post production we start with a simple "canvas" to do a color grading over specific group of layers by adding an adjustment layer on top and placing the needed effects over it (so you can dynamically change it at any time during production) and THIS is what I tried to SHOW on this file, based on the first file by noah since it was the most simple for me to look at.
I call this "FAKE GRADIENT" because it is probably NOT how an actual programmer will do this, also I'm not interested using the SPRITE Gradient way on a FULL canvas, because it will add extra space "size" to the saved file project for the user, also since it's already built-in and can be used with the Drawing Canvas with more Dynamic way to manipulate it using true-colors instead of a sprite.
As you can see, on the MIDDLE this is what I FAILED to achieve, covering the FULL area with gradient.
on the RIGHT is I show how it SHOULD look like but I played with the numbers on the Drawing Canvas Gradient and couldn't get to the same result...
I wonder if anyone can have a look and make the MIDDLE drawing canvas to look more like the RIGHT one because I believe that I can't get the covering numbers right...
The final goal is to cover FULL LAYOUT SIZE with the canvas + gradient and not just a tiny cube which makes the quality looks smooth and amazing... color grading with less than 32bit true color covers a full screen may look REALLY BAD that's why I mention this.
Play around with the color wheel, and look at the Middle and the Right examples to see what I mean:
DOWNLOAD - Color Grading Project
I'm curious to see this "Fake" way works on the drawing canvas without a SPRITE gradient!
please feel free to share your versions :)