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Smoke renders as transparent in OpenGL render
Closed, ResolvedPublic

Description

System Information
Archlinux
Nvidia 7900GT

Blender Version
Broken: Blender 2.69 Release (from arch repos)

Short description of error
Smoke appears transparent when rendered with the OpenGL render.

Exact steps for others to reproduce the error
Based on

  1. Simulate the smoke
  2. Render with the openGL render
  3. Smoke is rendered as transparency

Event Timeline

Ellwood Zwovic (gandalf3) set Type to Bug.
Ellwood Zwovic (gandalf3) created this task.
Ellwood Zwovic (gandalf3) raised the priority of this task from to Needs Triage by Developer.
Thomas Dinges (dingto) triaged this task as Normal priority.

I cannot confirm this on Windows 7 x64 with Geforce 540M, both the smoke sim and the OpenGL render look fine.

Also looks fine on Mac OS X 10.9 with Intel Iris Pro.

Here's a related post blender stack exchange.

Tested with an official blender.org build, still happens.

I'm on FreeBSD -

While a smoke only sim renders fine, when the inflow is set to fire or fire & smoke it shows up as transparent in an opengl rendering. Be sure to update the cache or bake after changing inflow type.

Maybe this is *nix opengl issue.

This began in 2.67 - 2.66 did not exhibit this issue.

Looking more at this, what is happening is that the fire is cutting the alpha channel through the entire opengl render even the background. Like it's using the fire for a mask. The full colour exists in the rgb only display.

What I see is this

Steps -

  • Load Factory defaults
  • select cube and apply quick smoke
  • select original cube and change smoke inflow to fire
  • click opengl render

Tested with different settings on arch.

Setup steps are the same as @Shane Ambler (sambler)'s:

  1. Load factory settings
  2. Apply Quick smoke on cube
  3. Simulate to frame 30

With the flow cube set to smoke I see this:

For Fire+Smoke I get:

And for only Fire I get:

So it seems fire is okay, only smoke is rendered transparent.

In addition to sambler's note about masking anything behind the smoke, it even seems to mask object in front of it:

My system: Windows 7 Profesional x64, nVidia Geforce GTX 660

With the attatched file everything works fine.
Just when using fire or fire+smoke it renders some parts as transparent.

Smoke:

Fire:

Fire+Smoke:

I also noticed that the domain renders (if you set alpha to transparent) not transparent as it should. Instead it renders as a big black box:

Viewport rendering is convenient and using alpha can work too, but drawing volumetrics with correct alpha for opengl render is just not supported and its not needed for using smoke in the viewport.

The problem is caused by draw_smoke_volume Using glBlendFunc(GL_SRC_ALPHA, GL_ONE); but from what I can see this is needed to draw smoke correctly.

Closing, this as an unsupported feature.

Brecht Van Lommel (brecht) changed the task status from Archived to Resolved.

This is actually reasonably simple to fix, I did this already for transparent faces, now added the same code for smoke as well.