I want the wider bloom that I see in the viewport to be rendered. As you can see, the render is completely inadequate. I understand Evee and Compositor having different looks when it comes to bloom, but this is Cycles + Compositor. I should be able to render what I see.
The warning says the “Render passes not supported in the viewport compositor”… so then why does it look like it’s supported and working? Infuriating.
It’s never going to look the same as a render and it’s far from being a completed project. It is meant for quick previews so that you can get your game on without having to constantly render to get a sense of how your project is coming along.
If you don’t like it, don’t use it. Getting mad at it is like being mad at a dog for barking. The dog is simply acting according to it’s nature and so is the software. Any time you take a short cut there is going to be a trade off and that trade is where you are finding frustration.
Bloom in the viewport compositor is actually similar to how it works in Eevee. It’s also a temporary solution according to the devs, so it might change in the future.
Bloom effect is also affected by the camera’s passepartout setting.
Because in the compositor you’re not using any render passes, like the alpha or the noisy image output of your render layers node.
As of now viewport compositor is still a WIP. It’s good for simpler stuff like color correction, But theres still a lot of things that needs to be worked out.
OH! Chain the glare nodes. Easy.
Viewport preview ≠ render output.
Just like a book synopsis is not the book, a movie teaser preview isn’t the movie, and a picture of a pizza tastes far different than a real pizza.
at least eating a picture of a pizza doesn’t set off my blood sugar. 
