Issues with with Canvas rendering

[whirlywhopter]

NOTE: IF YOU DO NOT ATTACH A SEQUENCE THAT DEMONSTRATES YOUR PROBLEM THEN THERE IS A HIGH PROBABILITY YOUR ISSUE WILL JUST BE CLOSED AND NOT INVESTIGATED.

Describe the bug
It appears that canvas mode is not rendering correctly in situations with multiple layers in version 15 but these types of combinations rendered correctly in earlier versions. It seems that layer blending settings may be getting lost when stacked effects are rendered causing strange rendered output with more complex layered effects. The issue is occurring with new sequences created in version 15 and I assume will impact existing sequences created in earlier versions as well.

To Reproduce
Steps to reproduce the behavior:
(and/or link to a short video showing the problem with audio track describing what you are doing)

1. From a clean show directory, create a layout with a single matrix. In the attached test sequence, I created a 192x192 matrix.
2. Create a new sequence, simple timing track and add multiple layers to the test matrix (I added 10)
3. Create some effects (I used shockwave) in at least 2 of the lower layers so that they overlap. (I used a shockwave effect). Set these effects to "Additive" layer blending.
4. Create another effect above these such as the pinwheel effect
5. Create an "Off" effect, with the style Black->Transparent, select "Canvas" and select only the layers for the shockwave or whatever effect was used in step 3. Unselect all other layers in the canvas settings so that only these layers are included. Set the layer blending to "Brightness"

This should render as the portion of the effect in step 4 that would be shown by the combination of effects included in the canvas selection as expected.

To create the issue:

6. Add another "Off" effect above all of these. Set the option Black->Transparent, enable canvas and select all but the layer blending layer

This should not change anything in the rendering since it is simply including all the layers below the "Off" effect with canvas enabled but this is not the behavior observed. It actually renders showing both the earlier output and the shockwave effects themselves which should not be displayed. I have seen this same type of behavior on multiple different combinations of effects that rendered as expected in previous recent versions of xlights.

Versions (please complete the following information):

• OS: MacOS 26.5.2 (25F84)
• xLights version: 2026.15

Additional context

Canvas Issue v15.zip

Attachments

• If associated with a crash please attach/link to a dropbox containing the crash log that was produced
• If it crashed but no crash log was produced please use Tools Menu/Package Logs and attach/link to a dropbox containing the resulting zip file
• If the error relates to rendering an effect or a crash while sequencing please use Tools Menu/Package Sequence and attach/link to a dropbox containing the resulting zip file

If you would prefer not to post your sequences publically please say so and be ready to PM them to one of the developers when asked.

[derwin12]

Unless I messed up .. I tested this sequence with current vs 2024.12 vs 2024.01 and it renders the same way.

[derwin12]

We think this might be the flaw in the logic "enable canvas and select all but the layer blending layer". Doing so reverses the work of the lower Off effect "groupings". You just want to include the layers above and incl. that off effect. Not the lower shockwaves and pinwheels.
It doing the same in 2024.01 and is it in the current version.