I'm trying to have a grease pencil fade in and out over a number of frames. I'm able to get this behaviour in the blender viewport, but not when I render. I've created a minimal example which is available here:

The minimal example has a grey square, drawn in the default "Lines" layer of the default "Stroke" grease pencil. The opacity of this layer is set to transition from 1 at the start to around 0.1 at the end. When I play in the blender viewport, I see a smooth transition. When I hit "render animation", I see no change in opacity for different frames, and the rendered opacity matches whichever frame I have selected in the UI. "Render animation" will still correctly render motion, if I add location keyframes, but the opacity still behaves in the described manner.

Is there a way to make the render output respect the transition between opacity values?

Steps to create the minimal example:

  1. Draw a square in a new 2D animation
  2. Set end frame to 20 in the timeline
  3. Create a keyframe for the opacity property of the "Lines" layer, at frame 0
  4. Create another keyframe for the opacity property of the "Lines" layer, at frame 20
  5. In the graph editor, drag the opacity at frame 20 down to around 0.1

This appears to have been a bug in blender 2.81. The example above behaves as expected in blender 2.82.

  • $\begingroup$ Possibly better suited to a comment on question. Questions re bugs in blender are regarded as off-topic, and it is suggested they be reported to the official bug tracker. As mentioned it appears tho, this one has been fixed. $\endgroup$ – batFINGER Mar 5 '20 at 14:49
  • $\begingroup$ I initially wasn't sure if this was a bug, or a misunderstanding on my part about how rendering works. Do you know of a more appropriate forum for discussing issues when I'm not sure whether there's a bug in blender or a problem with my use of blender? I'd like to respect the rules and etiquette of this site! Thanks. $\endgroup$ – Ed Wagstaff Mar 5 '20 at 15:22
  • $\begingroup$ Wouldn't worry about it too much. The "powers that be" (other users) will decide if it be closed or not. Seems to me worth marking as about a bug, since it appears to be fixed and you were spot on, on method. (Hence the upvotes). When not sure, I would err on a question here rather than an official bug report too. $\endgroup$ – batFINGER Mar 5 '20 at 15:35

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