Add/Sub blend mode broken in Tile Sampler?

[mvijfwinkel]

I use a Tile Sampler node set to 'Add/Sub' blending, the documentation says:

- Foreground pixels with a value higher than 0.5 are added to their respective background pixels.
- Foreground pixels with a value lower than 0.5 are substracted from their respective background pixels.

But the Tile Sampler seems to be blending with 'Add' instead.



Please note that the black parts from the input are not being blended with Substractive blending. The regular Blend node does do this correctly.

What am I doing wrong? Example scene attached.

[mvijfwinkel]

I still haven't got this figured out. Allegorithmic support said that this is not a bug, because the Add/Sub blend mode only applies to blending between the pattern (not the background). However, I still cannot get it it work.

I made a new test file with a pattern containing only black and neutral gray.



The documentation says:

The Add Sub blending mode works as following:
Foreground pixels with a value higher than 0.5 are added to their respective background pixels.
Foreground pixels with a value lower than 0.5 are substracted from their respective background pixels.

Since my pattern has only values lower than 0.5, all blending should be substractive. When I input this pattern in the Tile Sampler (or Tile Generator) with Add/Sub blending, then the result has white colors:



Note that the same setup with the regular Blend node and 'Add/Sub' blending has no white colors, and the Blend node with 'Add' blending looks exactly the same as the Tile Sampler output.

I looked at the FX map for the Tile Generator node, the function that controls the blendmode is overriding the Add/Sub blend mode (3) to a Add blend mode (0):



So it seems Add/Sub is broken, and for the Tile Generator node it is being disabled/overridden on purpose?

I've attached the test file.

[mvijfwinkel]

*Bump*

I'm still looking for an asnwer to this (either a solution of confirmation that add/sub is broken).