2.10 layer composition options and modes

[Ofnuts]

The 2.10 release notes say:

Quote:Compositing options for layers are exposed to users now, and all layer-related settings are finally available in the Layer Attributes dialog.

If I sort of guess the Blend space/Composite space, I wonder what the "Composite modes" do?

These notes also mention new blend modes, but I'm still wondering what these do: Erase, Exclusion, Merge, and Split. Exclusion seems to be some kind of "xor", but I can't even find an case where the other three have a visible result.

[mholder]

Clip to backdrop and intersection seem to work like a layer that gets the alpha value of the pixels in the visible layers under it.

Now you can over ride it and not have it clip, or have it clip for any mode.

It can't work like a true clipping mask, because it clips all visible pixels in all layers below it. It is very strange and not very useful. Clipping masks would be very useful in Gimp if someone would for a few minutes study PS.

[Ofnuts]

(06-17-2020, 12:03 AM)mholder Wrote: Clip to backdrop and intersection seem to work like a layer that gets the alpha value of the pixels in the visible layers under it.

Now you can over ride it and not have it clip, or have it clip for any mode.

It can't work like a true clipping mask, because it clips all visible pixels in all layers below it.  It is very strange and not very useful.  Clipping masks would be very useful in Gimp if someone would for a few minutes study PS.

Erase seems to be an (anti-)clipping mask, it makes transparent all pixels under its non-transparent pixels. If you put it in a group it only
applies to layers below it in the group. But Split has the same result... so why both?

[Krikor]

Summarizing some of what I found in my research on Composite Mode Options.

Some clarifications for a better understanding of the image below:

Only in the first picture (top left) the composition on the left shows the green circle in Normal mode and the Composite Mode in Auto.

In the other figures, the green circles on the left are in Addition mode with composite Mode Auto.

In all other figures the green circle on the right is in Addition mode, and Composite Mode is indicated by the label.

   
Most of the information contained herein was obtained from:
https://mail.gnome.org/archives/gimp-doc...00009.html

[tmanni]

The 4 compositing modes are some equivalent to the Porter Duff compositing operators :
Union -> Source Over
Clip to Backdrop -> Source Atop
Clip to Layer -> Destination Atop
Intersection -> Source In

Technical details here https://www.w3.org/TR/compositing-1/#por...goperators

From the commits description:

- app: add merge layer mode
   
   Merge mode lays the source layer on top of the destination, same as
   normal mode, however, it assumes the source and destination are two
   parts of an original whole, and are therefore mutually exclusive.
   
   This is useful for blending cut & pasted content without artifacts,
   or for replacing erased content in general.

- app: add split layer mode
   
   Subtracts the source layer from the destination, such that
   recompositing the result with the source using merge mode
   reproduces the original content.