fading edges working only on top and left

Question

I made a custom ImageView that supports basic scrolling through calls to View.scrollBy() in a GestureDetector. I wanted to add some feedback on the reaching of scrolling bounds so I enabled fading with:

setVerticalFadingEdgeEnabled(true);
setHorizontalFadingEdgeEnabled(true);

but the fading works as I expected only on top and left edges, while bottom and right ones don't fade. I'm sure those edges aren't off screen because the view is set to fill_parent in height and width. So what's wrong?

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EDIT: enabling only vertical/horizontal fading edges confirms that only top/left edges get drawn. Now I'm trying to read View.java (6870 an on)...

Answer 1

It seems that the problem is in getBottomFadingEdgeStrength() and getRightFadingEdgeStrength(), or better, in the fact that I didn't override them to work with my custom view.

These protected methods tell view's draw() when to draw the fadings (and how strongly -- see what a ScrollView does when you get close to the scrolling limit).

For top and left edges it's easy because the limit is 0 in both cases and the default implementation works (in its on/off manner), but for the other two I need to override the methods to take into account my own scrolling bounds (in my case, the drawable dimensions).