Re: [Gimp-gui] Multi-layer selection

[Ofnuts <ofnuts gmx com>]

On 10/10/15 18:50, Jehan wrote:
> > Good question. The "link" selection applies across different types of
> > objects
>
> I never realized this. You can indeed link and move together layers 
> and paths for instance. This by itself says to me these are very 
> different concepts.

Actually fairly useful. Transform tools on paths (especially text paths) 
aren't very easy to use because their reference is the image and not the 
layer from which you produced the path. But you can link the path and a 
copy of the layer, and use the transform tools on the layer, and then 
discard the layer and use the transformed path...

> Actually a new question can be to define what is a layer link exactly! 
> The doc says 
> (http://docs.gimp.org/en/gimp-image-combining.html#gimp-layer-properties): 
> "chain icon, which enables you to group layers for operations on 
> multiple layers (for example with the Move tool or a transform tool)."
> And that's it. It does not look like a very proper definition.

As far as I can tell, it just means that a transform tool (and that 
includes moves) is applied to all items linked to the one that was used 
with the Transform tool. Layer groups also allow this (when you act on 
the group), but only between layers.

> For instance, when I hear operations, I think also "filters" (now even 
> renamed GEGL *operations*). Shouldn't these be applied to all linked 
> layers then, according to the above definition?

This would not make sense for paint tools (because you would be painting 
at the same spot on all layers....). This could make sense (sometimes) 
for Color tools (by applying the same correction to all layers). But the 
links are somewhat permanent, that would make them work for everything, 
and since there are plenty of cases where this is not wanted, the user 
would have to drop links, and then reinstate them later... This gets 
messy, unless we have a "mode" to enable/disable repeating action on 
linked items. Speaking of GEGL, whatever is done here will have to be 
included in the GEGL nodes model.

> > so could be considered different (what happens to linked paths
> > when you just reorganize layers in the layers list? What happens when
> > you delete some thing in one list, should linked items of other types
> > be deleted too? IMHO the current "links" are a bit insufficient anyway
> > because you cannot permanently link two distinct sets of items, I'd
> > love to have a way to tell Gimp that these two layers and this path
> > should always be transformed together, while these three other layers
> > and that other path are also always related.
>
> It's true. In other software, like Blender, Inkscape or Scribus, you 
> can "group" items together (not layer groups, this is independent to 
> the stack position). Then these grouped items are considered the same 
> item for most operations (while still retaining the ability to be 
> ungrouped, so this is not a merge).
>
> This said, when these items are grouped in other software, that 
> usually mean you cannot modify them at core anymore (for GIMP, it 
> means you can't draw into a linked layer). On these aspect, we are 
> different, and maybe more powerful.
>
> It very much looks like our concept of "links" except that we only 
> allow for 1 link group at a time. And also it is not consistent since 
> GEGL ops don't work on all items of a link group.
> It may indeed be worth reviewing and improving the link concept while 
> making its definition clear.
>
> > Repeating the action on selected items can be left to the scripts and
> > plug-ins, if they are provided an API to retrieve the selected items.
>
> Yes. Actually a lot of our API calls don't do what we would expect 
> from the equivalent graphical usage. For instance saving as XCF in the 
> API does not clean the dirty flag (there is a separate call for this). 
> It can be the choice (and maybe already is) to say that the API should 
> stay as low level as possible and not automate too much, allowing more 
> freedom to scripts.

I'm all in favor of a rather low-level API with utility/helper functions 
to make the more frequent use cases easy to code.