Corona MTL Advanced options: "Visible in masks" effects alpha channel

[rfletchr]

Were rendering some shots at the moment of an aircraft that has to be composited onto a backplate. The cockpit has a number of masks that we need for comp, so we disabled  the "visible to masks" option for the Glass Canopy's material. unfortunately not only does this remove the glass from the render elements but it also gives it zero alpha in the beauty.

This makes it pretty much impossible to composite a backplate behind the plane.

[rfletchr]

I've clarified the report. I hope im right reporting this as a bug, It doesnt seem a usefull feature if the materials contribution is lost when compositing

[maru]

Sorry but it is hard for me to imagine what is going on by only reading the description. Can you post some images of what is happening, and what you think should be happening if it worked fine? It doesn't have to be this specific model, it can be something simple that illustrates the problem.

[Ludvik Koutny]

Unfortunately, alpha masking option when it comes to refraction are currently very limited in Corona. After next rewrite, it should be possible to easily propagate refraction into masks.

One PITA workaround would be to disable render elements, and render beauty only with Canopy material that has enabled masks visibility, and once rendering of beauty ends, render masking elements using "render masks only" or the string option bool shading.enable = false in case you are submitting it to render farm.

It's planned to be fixed, but unfortunately still not here.

Sorry about that :(

[rfletchr]

My Apologies Guys, my original message was very poorly explained. Hopefully this clears up the issue.
We need the glass to be visible the the beauty has had the Alpha premulted.




Rawalanche
We're quite happy to live with thin-wall glass for this sort of stuff. Is enabling this mask fundamentally changing how corona calculates the alpha channel?

Sorry but it is hard for me to imagine what is going on by only reading the description. Can you post some images of what is happening, and what you think should be happening if it worked fine? It doesn't have to be this specific model, it can be something simple that illustrates the problem.

Not suprising i explained it terribly ;)

[Ludvik Koutny]

Rawalanche
We're quite happy to live with thin-wall glass for this sort of stuff. Is enabling this mask fundamentally changing how corona calculates the alpha channel?

I am not quite sure what you mean by enabling mask in this case :)

[Ondra]

I am still not sure what is the problem here... alpha counts as one of render channels, so disabling the checkbox removes it

[pdaniun]

I think this is the problem, the glass around those candles is set to be transparent in alpha, and it is not transparent, just black. When alpha behaviour is set to default, the channel is transparent according to refraction settings of the material. Thus there is no way of removing the material from being displayed in alpha channel completely without making it invisible in the beauty pass or cutting a great big black hole in the alpha channel.

[Ondra]

can you provide a scene for this?

[pdaniun]

Uploaded, and rendered for explanation. The file is 1446470063_alpha_test.zip
I think the middle Teapot should not be black in the alpha channel but invisible.

BTW, a minor bug: When choosing the render environment map from the Environment window, and selecting a new "CoronaBitmap" there is no "Browse images for input" window appearing. One has to drag the new Corona Bitmap to the Material Editor window to be able to select the source file. Same thing happens with setting the environment and various overrides in Render Setup window|Scene Environment.

[Ondra]

we know about the CoronaBitmap not popping up, unfortunately it is a pretty tough call, because 3dsmax is giving its own bitmap some exclusive treatment to make it happen... we are not sure if we will be able to do the same without Max support

[Ondra]

Ok, what you are requesting is not supported by Corona, and rpobably wont be for some time. Hopefully we will rewrite to support arbitrary AOVs one day. In the meantime I changed the wording so it is not confusing - from transparent/solid to black/white