09-28-2021, 08:32 AM
@ Geocide
You have set up nicely
What you can do is
Go to the port layer then Layer -> Transparency -> Alpha-to-Selection. That will select all the red block
Go to the above port layer then Layer -> Transparency -> Subtract from Selection. Using that will keep any semi-transparency in the selection.
You can check the effect with a fill: 30 second demo: https://i.imgur.com/iZlsUbM.mp4
You have set up nicely

Go to the port layer then Layer -> Transparency -> Alpha-to-Selection. That will select all the red block
Go to the above port layer then Layer -> Transparency -> Subtract from Selection. Using that will keep any semi-transparency in the selection.
You can check the effect with a fill: 30 second demo: https://i.imgur.com/iZlsUbM.mp4