[FEATURE] gradient colors

Is your feature request related to a problem? Please describe.
only a static color for a foreground/background is allowed right now, which limits creativity

Describe the solution you'd like
being able to set the foreground/background color, to a horizontal/vertical/diagonal gradient.
ideally, we would have a Gradient trait with a fn get_color(pos: XY, size: XY) -> Color that would allow users to make their own gradients which would fit their needs

Describe alternatives you've considered
if having gradients isnt very important you can just use a static color, if you need them the only option is using the Canvas or writing your own View

Additional context
was already mentioned here, seems like theres no progress on it tho
i could write the code for this, but im not sure what the api should look like
heres a gist with a proof-of-concept

[gyscos]

Hi, and thanks for the report!

Being able to use gradients sounds very fun indeed! I haven't spent much time thinking about it though so I'm not sure yet what the API would look like - in particular:

• How to unify the styling with the current flat colors styles
  • And possibly with a future "opacity" concept where views can be partially transparent, letting lower layers be seen through.
• How to make it easily configurable in json/yaml for theme files
• Support for "absolute positioning" gradient, where the gradient is defined on the entire terminal window but only applied to a single view

[gyscos]

The latest couple of commits bring some gradient features:

• cursive::style::gradient defines a few new types:
  • Linear is a piecewise 1D (linear) gradient (converts a float between 0 and 1 to a RGB color).
  • Angled, Radial and Bilinear are 2D gradients: they assign a color to each cell of a grid (sometimes using a Linear internally).

A few places make use of these:

• cursive::utils::markup::gradient can apply a Linear gradient to a StyledString, either for the front or background color.
• cursive::views::GradientView takes a 2D gradient, and applies it to a wrapped view, either using local coordinates (the gradient stretches to the extend of the view), or "global" coordinates (the gradient is calculated using the absolute position of the view in the terminal), which can give nice effects when used by multiple views.

Finally, a gradient example has been added, which uses all of these.

thanks! Is there anything yet to add, or can we close the issue?

[gyscos]

thanks! Is there anything yet to add, or can we close the issue?

Well, it depends if your use-case was solved :)

There's an endless list of potential improvements: support for more 2D gradients (diamond, conical, ...), composite 2D gradients, LCH/HSB/HSL color space interpolation, more gradient presets, user-expandable list of presets that can be loaded by the builder module, animated gradients, ...