Hi LIMN,

On Sun, Apr 26, 2009 at 7:07 PM, LightningIsMyName
<lightningismyn...@gmail.com> wrote:
> Hello,
>
> Gimp 2.6 allows to use brush dynamics to control opacity, size, hard and 
> color.
> These features greatly increase the drawing capabilities of gimp, and many
> users find them very useful.
> However, we don't have any way to access these from inside the PDB...
>
> I think that it would be nice to be able to access these using the PDB, 
> however
> I'm not sure about the right method:
> Do we want to allow the user to specify velocity, and pressure for each coord,
> or should we use the "emulate brush dynamics" feature (the same one we have in
> the libart stroking)? Personally, I believe that the "emulate brush dynamics"
> is the right method.

We should definitely make dynamics available, but IMO both of these
methods is quite unsuitable and would only add to the current
inconsistencies of the pdb interface to paint tools.

In my opinion this is what needs to happen:
 A) Migrate paint tools at least partially to GEGL (so that the actual
rendering of strokes is done by evaluating a 1-node GEGL graph). This
will help us define a consistent, expansion-compatible way of
communicating and storing stroke information.
 B) Make a system for handling both full strokes (where each point
specifies parameters such as brush scale, rotation, aspect ratio,
spacing directly) and simple strokes (where each point only specifies
the 'source' information -- pressure, velocity, angle, etc.), and
converting simple to full strokes
 C) Work out a way to pass this information through the PDB, in a
backwards + forwards-compatible way
      -- so that older scripts work in newer versions because their
missing fields are automatically expanded and filled in with sensible
default values, and that newer scripts work (in a limited sense) in
older versions of GIMP.
 D) Provide a method of constructing and communicating GEGL graphs
through the PDB.
      This can be used by scripts to actually do the required painting.
 E) Use it (and deprecate the current 'gimp-paintbrush' etc API)

I also think we need to look harder at our current inability to
communicate various tool options such as Jitter,  Color from Gradient,
 and Incremental; possibly communicate these via a keyword-argument
sort of interface (ala Python)

>
> I'm willing to try to write a patch to add this for gimp-paintbrush,
> gimp-airbrush, etc.
Do you understand that you must not change the api of gimp-paintbrush,
gimp-airbrush, etc? Because that would break a lot of scripts and
plugins. This is part of the problem with the current PDB interface to
tools; supporting new options must be done through additional PDB
functions.

David
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