ID:2937005
 
Resolved
The displace filter now accepts a flags argument, with FILTER_OVERLAY as the only supported flag. If used, the displaced pixels will be overlaid on top of the original image.
Applies to:DM Language
Status: Resolved (515.1643)

This issue has been resolved.
It would be very useful for some shadowcasting effects to be able to set displacement map to copy pixels instead of pulling them.
+1, would be cool
I don't quite follow what you mean. How would you define "copy" here?

The way the displacement filter works is that it reads the mask to figure out a direction, and the shader just says "grab the pixel from over there".
In terms of how displacement filter works, "copy" will probably mean "grab the pixel from over there and left a copy of it there"
Or, maybe, in other words, "don't grab but copy the pixel from over there"
In response to Vallat
Vallat wrote:
In terms of how displacement filter works, "copy" will probably mean "grab the pixel from over there and left a copy of it there"

That doesn't make sense.

When the displacement filter is grabbing a pixel from somewhere else, that somewhere-else—if it's covered by the mask as well—is also doing that. Every pixel under the displacement mask is using that mask, independently of one another.

If you want pixel A to copy pixel B due to displacement, but pixel B to be left alone, then at pixel B's location the displacement mask has to be neutral.
Lummox JR resolved issue with message:
The displace filter now accepts a flags argument, with FILTER_OVERLAY as the only supported flag. If used, the displaced pixels will be overlaid on top of the original image.