Feature request: User-defined control panel for script snippet

[pierrelabreche]

Would it be possible to let users define combinations of transformations driven by overall sliders.

1. Ability to drive a transformation's slider using an expression

• A menu item to link to an expression could be defined by right-clicking a slider marker
• When a slider marker is controlled by an expression, the marker icon is changed to indicate that it is driven by an expression
• The expression driving a slider can refer to the value of another slider in an upstream transformation
• Expression macros can refer to the value of a slider marker ( e.g. black and white markers)
• Expression macros can refer to the value of a color line control

2. A special transformation, "Custom control panel", can drive a script snippet :

• One or more sliders can be defined in a custom control panel
• The scale of a custom slider has a user-defined range
• A custom control panel has an amount control ( and a mask button ), like those of built-in transformations
• The output image of the custom control panel is the output image of the last transformation of the associated script snippet, modulated by the custom control panel's amount slider and mask.

Example of use : User-defined "Contrast Color Range"
This would allow to define a color transformation whereby the intensity of a hue is boosted, while darkening the opposite hue, that is 180 degrees apart. One slider directly controls the hue to be enhanced, while indirectly controlling the hue to be darkened (using an expression).
User would be able to fine-tune the hue to be enhanced and its opposite hue using a single control.

[pierrelabreche]

This feature, if developed, would enable users to create complex filters and their associated control panels. For example, similar to Nik collection's Color Efex

• Contrast color range, with sliders for : Color, color contrast, luminosity, contrast
• Reflector Efex, with sliders for : Light intensity, Transition, Position, Direction ; with enumerated choices for : Method

Rather than dispersing the sliders or other controls in individual transformations, the overall control panel would allow adjusting the visual effect in one place.

If the separate feature "interactive adjustment display while a control is handled" ( viewtopic.php?f=4&t=3163&p=12254#p12254) is also enabled, users could see instantly the effect of adjusting custom sliders.