[cairo] [RFC] Color space API (partial proposal)

[Andrea Canciani]

On Mon, Feb 22, 2010 at 3:35 PM, Kai-Uwe Behrmann <ku.b at gmx.de> wrote:
> Am 22.02.10, 12:28 +0100 schrieb Andrea Canciani:
>>
>> On Mon, Feb 22, 2010 at 11:10 AM, Kai-Uwe Behrmann <ku.b at gmx.de> wrote:
>
>>> cairo_color_t/cairo_t meta data:
>>> Rendering intents are defined by the ICC standard. But as the system is
>>> evolving several additional arguments are in the queue or will become to
>>> that. Think of black point compensation (BPC) typical supported by most
>>> colour managed linux graphics applications, or CMM specific options like
>>> lcms' preserve black one.
>>> So rather than placing this stuff into cairo_t
>>> +cairo_public void
>>> +cairo_set_render_intent (cairo_t                      *cr,
>>> +                        cairo_render_intent_t  render_intent);
>>> +
>>> I would find it much more adequate to place it into cairo_color_t.
>>> cairo_public void
>>> cairo_color_set_render_intent (cairo_color_t         *color,
>>>                               cairo_render_intent_t  render_intent);
>>
>> Since rendering intent is actually used only when a color space
>> conversion is done,
>> basically we can choose whether select a rendering intent for all the
>> sources
>> we are going to use (colors, patterns) or for all the destinations
>> (cairo_t, gradients (they
>> convert color stops to the pattern color space)).
>
> I think now its a "and" and not a "or". On entrance of the blending space a
> conversion has to take place with all options. And on converting to the
> output colour space the same again, but possibly with different options.

It was an "or" (exclusive or, actually). Now I'm sure rendering intent
should only
be specified for destinations as (from pdf reference" 11.7.5.3 Rendering Intent
and Colour Conversions"):
...
The rendering intent influences the conversion from a CIE-based colour
space to a target colour space, taking
into account the target space’s colour gamut (the range of colours it
can reproduce). Whereas in the opaque
imaging model the target space shall always be the native colour space
of the output device, in the transparent
model it may instead be the group colour space of a transparency group
into which an object is being painted.
The rendering intent is needed at the moment such a conversion is
performed—that is, when painting an
elementary or group object specified in a CIE-based colour space into
a parent group having a different colour
space.