Sorry, I cut the top off in the screengrab. That last post was in the compositor. All you have to do is render your view then open the compositor, and find the nodes as I showed, it will drop a rendered png to the directory you pick, as seen in the windows viewer…the reason it shows a white background is the transparent PNG is on a white background…
I copied your Principled Volume shader, with just a bit of tweak to work with the VDB I grabbed…
…OK, then it’s easy to say, grab a VDB render it and save the render as a transparent PNG… Show us, ignorant people, just how easy it is!
As I’ve already said, but apparently neither of you read.
There’s nothing special about working with VDBs when it comes to transparency. No special technique or magic button. If it doesn’t work then a mistake has been made and without a copy of the blend file it’s time consuming to guess at issues when the user is a novice. Particularly so when they can’t tell the difference between a material tree and a compositing tree.
And to diagnose the mistake.
Let me clarify when you say " Aside from enabling Film > Transparent" , could you also mean EXCEPT enabling Film > Transparent…?
as that is a LONG outstanding debate over on Developer.Blender.org
Transparent Background is a necessity for @Alessio_Tyrell that is the whole point…
I also ask you to read our comments and look at the images…we know how to render a transparent VDB …and save an image as an RGBA PNG… obvious as to what we showed…
But with a transparent BACKGROUND…is not working! So show how YOU do it!
I was seeing unexpected results when previewing the alpha channel of my render result:
While checking out the shader I noticed the principled volume shader density socket was unused and set on 0. I’m guessing cycles ignores emissive volumetrics for generating alphas. Once I plugged in the value I was using for the emmision strength input into the density input, cycles was able to generate a proper alpha result.
Since altering the density value changed the look of the fire quite drastically, doing the following in the compositor allowed me to keep the look I want, but export with transparency. Bit of a dirty fix but works well enough.
This isn’t a bug. The PNG image format, because it uses straight alpha internally, and requires an alpha divide / multiply step, is incapable of storing additive pixels—that is, pixels with RGB values but little or no alpha. Not Blender’s fault.
If you want to export additive pixels, use EXR, or export your PNG on black and use Add mode—if you have no alpha, that’s the result you would have gotten anyway: the math is identical.
