Make a gradient follow a specific path on a shape

Question

I'm a beginner AI user and what I'm trying to do is to make a gradient follow a path on a specific shape. This is the shape, I want to fade it from the line to the end of the loop:

The shade would simply be from white to transparent and it should start fading from the red line to the end of the loop.

If I simply apply the gradient to fill the shape it goes from left to right at whatever angle is given, but I want it to follow that specific path. I already found this question but I don't have an actual inner path, it's more of a shape filled with white and with no stroke.

Is there a way to do so?

Thank you for the help, have a good day.

Answer 1

The only way to do this in Illustrator would be to use a gradient on path outline (stroke), instead of shape. (Post CS6)

You will have to recreate your path as a line instead of a shape.

Draw a path in the shape you want then apply a gradient to the stroke.

In the Gradient Panel Window→Gradient (Ctrl+F9), you want to switch it to Apply gradient along stroke

You will want to set the stroke thickness up in order to see your result.

Here's a quick one I did:

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I recognize that converting that shape into a path is actually quite challenging, here's a rough (eyeballed) sample you can use, I'm sure there's a more mathematical way to create this, but here's the Illustrator file where you can see the process I used to create it.