Re: [Gimp-developer] Overlay Mode - fix.

["Guillermo Espertino (Gez)" <gespertino gmail com>]

El 14/11/12 12:43, yahvuu escribió:
> > I was thinking about adding it along with the lock buttons. A checkbox
> > labeled "legacy mode" that adds the needed gamma correction nodes to all
> > the layers and replaces the new overlay for soft-light is all that we need.
> > I can't see a reason for having legacy blending modes co-existing with
> > native.
> A good reason for co-existence is that all the new blending goodness will
> be available when touching up/building upon prior work.
>
> A global switch between old/new blending characteristics might also turn into
> conflicts with future developments. With co-existance, we're on the safe
> side in that regard.
>
> In the latter case, we're only talking about when the legacy modes show up
> in the UI. With a global switch, we would be be putting constraints on the
> composition.

I guess we can put this issue in simpler terms and see if we agree:
- Linear is the way blending should be done. The most basic compositing 
operation, which is the porter-duff alpha over works better in linear space.
it's extremely easy to see this just blending a couple of saturated 
colors. The semi-transparent pixels tend to add a dark fringe if you 
blend them in non-linear.
- Legacy is legacy. For some reason which no longer applies blending was 
done in non-linear space. There is no other reason for using non-linear 
blending other than:
a) support legacy GIMP
b) support applications that still use blending in non-linear space. Web 
browsers, for instance.
- This brings two problems:
a) How to deal with old GIMP files
b) How to provide a reliable web workflow without packing the UI with 
duplicated menus.

I think that making linear and non-linear blending coexist is the worst 
thing that can be done, because it creates a complexity which is not 
really necessary.
It's not putting constraints on the composition. You can use any 
technical errors as creative tools, but making the UI of the "proper" 
tools because of that is a mistake. It's like asking to keep a buggy 
filter as an alternative "because I like how it looks".
Other tools should be provided to re-create the intended look, not 
keeping things that don't work as they should. And blending in nonlinear 
space probably falls in the latter.

After thinking about it for a moment, I can't imagine a better way to 
address this problem other than adding a special "mode" that makes all 
blends non-linear, but considering the need of a web-safe workflow, it 
probably shouldn't be named "legacy", but something more accurate like 
"Allow blending in non-linear space"

And if it's possible, only when that switch is selected, then show the 
alternative "old overlay", which only makes sense for legacy.

Gez.