Add kOfxParamPropColourManaged for colour-managed RGB/RGBA params (#158)

Add kOfxParamPropColourManaged, a boolean parameter property a plug-in can
set on an RGB or RGBA parameter to declare that the parameter's values —
including its default — are in the ACES2065-1 (AP0) reference colourspace
rather than an unmanaged, display-referred encoding. The values are
scene-linear and not constrained to [0..1], so a colour-managed host (or any
host that supports wide-gamut colours) can interpret and convert them
correctly. Plug-ins must check the set status: if the host does not implement
the property, they should fall back to old-style colour values. It defaults to
0, so existing plug-ins are unaffected.

- include/ofxParam.h: the property with its @propdef metadata (bool, dim 1),
  plus new ParamsRGB and ParamsRGBA property sets (the colour param types were
  not previously modelled in the property metadata).
- Documentation/sources/Reference/ofxParameter.rst: describe the property in
  the Colour Parameters section.
- release-notes.md: note the addition under 1.5.1.
- openfx-cpp/include/openfx/*: regenerated metadata, property sets, and typed
  accessors (scripts/gen-props.py).

Signed-off-by: Gary Oberbrunner <garyo@darkstarsystems.com>

Author: garyo

Documentation/sources/Reference/ofxParameter.rst

@@ -150,9 +150,25 @@ These are typed by :c:macro:`kOfxParamTypeRGB` and :c:macro:`kOfxParamTypeRGBA`.
 
 Colour parameters are 3 or 4 dimensional double precision floating point
 parameters. They are displayed using the host's appropriate interface
-for a colour. Values are always normalised in the range [0 .. 1], with 0
+for a colour. By default values are normalised in the range [0 .. 1], with 0
 being the nominal black point and 1 being the white point.
 
+A plug-in may set :c:macro:`kOfxParamPropColourManaged` on an RGB or RGBA
+parameter to declare that its values — including its default — are in the
+ACES2065-1 (AP0) reference colourspace rather than an unmanaged,
+display-referred encoding. These values are scene-linear and are not
+constrained to the [0 .. 1] range. This lets a host interpret and convert the parameter's colour correctly — for
+example to draw an accurate swatch, or to transform the value into its own
+working colourspace, or to give wide-gamut colours to the plugin. Hosts or
+plug-ins that do not support this property should treat the values as before.
+
+Plugins should check the return status when setting
+:c:macro:`kOfxParamPropColourManaged`; if the host returns an error,
+the plugin should continue to use and expect unmanaged colour values.
+
+See :c:macro:`kOfxImageEffectPropColourManagementStyle` and the
+related colour management properties for the native colour management
+config and its reference colourspaces.
 
 Boolean Parameters
 ------------------

include/ofxParam.h

@@ -421,6 +421,36 @@ The exact type and dimension is dependent on the type of the parameter. These ar
  */
 #define kOfxParamPropDefault "OfxParamPropDefault"
 
+/** @brief Flags that an RGB or RGBA parameter's colour values are
+colour-managed.
+
+When set to a non-zero value on a parameter of type ::kOfxParamTypeRGB or
+::kOfxParamTypeRGBA, the parameter's colour values — including its default
+(::kOfxParamPropDefault) and its current value — are expressed in the
+ACES2065-1 (AP0) reference colourspace, rather than an unmanaged,
+display-referred encoding. ACES2065-1 is the reference colourspace of the OFX
+native colour management config (see @ref ofxColour.h); values are scene-linear
+and not constrained to the [0..1] range.
+
+This lets a host interpret and convert the parameter's colour correctly — for
+example to draw an accurate swatch, or to transform the value into its own
+working colourspace, or to give wide-gamut colours to the plugin. Hosts or
+plug-ins that do not support this property should treat the values as before.
+
+Plugins must check the status when setting this property; if it's unimplemented
+by the host, the plugin should use and expect old-style colour values.
+
+This property is only meaningful on RGB and RGBA parameters and is ignored on
+other parameter types. It defaults to 0 (not colour-managed) so that existing
+plug-ins are unaffected.
+
+    @propdef
+    type: bool
+    dimension: 1
+    introduced: "1.5.1"
+*/
+#define kOfxParamPropColourManaged "OfxParamPropColourManaged"
+
 /** @brief Describes how the double parameter should be interpreted by a host.
 
    - Valid Values -This must be one of
@@ -1453,6 +1483,26 @@ changes a keyframe.  The keyframe indices will not change within a single action
       - ParamsNumeric_REF
 */
 
+/** @propset ParamsRGB
+    write: plugin
+    props:
+      - OfxParamPropColourManaged
+      - ParamsCommon_REF
+      - ParamsAllButGroupPage_REF
+      - ParamsValue_REF
+      - ParamsNumeric_REF
+*/
+
+/** @propset ParamsRGBA
+    write: plugin
+    props:
+      - OfxParamPropColourManaged
+      - ParamsCommon_REF
+      - ParamsAllButGroupPage_REF
+      - ParamsValue_REF
+      - ParamsNumeric_REF
+*/
+
 /** @propset ParamsChoice
     write: plugin
     props: