Gradient functions

[jarodium]

I would like to open this discussion on the topic of gradient functions.
As mentioned in #130 and taking #104 as the source base ( the gradient ) I was trying to create a gradient function with 2 distinct colors as a start and a end colors.

I ended up using the one color as the base ( and for the other color, I just added another gradient with composite2 ).
Taking from @jcupitt 's example, I ended up making some tweaks, just for "quality of life":

function fxGradient($image, $start, $end, $invert = []): \Jcupitt\Vips\Image {

    if (count($invert) == 0) {
            $invert = [
                    "color" => false,
                    "coord" => false 
            ];
    }
    # a two-band image the size of $image whose pixel values are their
    # coordinates
    $xyz = \Jcupitt\Vips\Image::xyz($image->width, $image->height);

    # the distance image: 0 - 1 for the start to the end of the gradient
    if ($invert["coord"]) {
            $d = $xyz[0]->divide($xyz->width);
    }
    else {
            $d = $xyz[1]->divide($xyz->height);
    }
                

  # and use it to fade the quads ... we need to tag the result as an RGB
  # image
  return $d
          ->multiply(!$invert["color"] ? $end : $start)
          ->add($d
          ->multiply(-1)
          ->add(1)
          ->multiply(!$invert["color"] ? $start : $end)
          )->copy(["interpretation" => "srgb"]);
}

My goal now is to add or remove more of the gradient to the image ( I mean that I want to put solid black at X% of the image and transparent black at Y%) , and I am experimenting on adding/removing extra "adds" and multiplies, and tweaking up with the divide to see if it looks nice.

I can also do rotations on the result of this function but the results are not quite I expected. I am sure I'm not doing it the proper way or perhaps the rotation may require some more solid colors to provide better results, but i'm pretty much happy with this function.

In my use case, I use lab as the interprepration, because i'm using hex colors and I require a conversion process that does not require many conversion steps from sRGB to LAB, and was told that LAB equals HSL and it was safe to use.

In time, and more testing I will keep this thread updated with other enhancements I've made.

What is your take in the gradient function?