Add a new boolean option, relativeToWrapper.

[MadsMadsDk]

This addition originates from the need to let movement be relative to a wrapper, rather than scroll position of a wrapper or the scroll position of the window.
We'll use the wrappers vertical offset, and subtract it from the scrollposition, to enable an effect, that feels like the element is relative to its wrapper instead.

Simply a boolean, telling us whether or not it should be relative to the container selected in the wrapper option.

[simgooder]

I just reviewed this as a potential fix, and for my use case, this seems to do the trick. I was half expecting this to support multiple wrapper options. I'll have to take further look when I get some time.
Your fix works as expected.

[salunet]

How can i use this for horizontal scrolling?

[MadsMadsDk]

This feature is currently only supported for vertical scrolling.

[salunet]

@MadsMadsDk can you make it work for horizontal scrolling?

[moeamaya]

@MadsMadsDk Should I merge or you interested in adding it for horizontal?

[MadsMadsDk]

@moeamaya You can merge this - I'll do another PR for horizontal if I get the time to look into it. Shouldn't be too hard though.

[lindsayweb]

Does relativeToWrapper still work with the current version of Rellax? When I add relativeToWrapper:true, the rellax elements stop moving. The transform CSS does not change on scroll.

[cristian-rodriguez-glb]

Same thing using wrapper: this.parentElement 😞

[one-juru]

This is a great addition, but it seems to be broken in the current version (if I'm not mistaken)

As far as my understanding goes, setting a wrapper will enable Rellax to use the scroll position inside the wrapper for the movement. If there is no scrolling inside the element which was set as a wrapper, Rellax won't move anything. This option (relativeToWrapper) is supposed to change that behavior, and instead still takes the scroll position of the body but calculates the difference between the body and the wrapper element, so that is seems as if the element only moves after the wrapper element is seen by the user. Is this a correct understanding of this option?

Using "relativeToWrapper" at the moment will result in the object being further down the page (so I can confirm that the initial calculation (body minus position of the wrapper element) still works) but it won't move and stick to the position that initially was calculated. If my understanding is correct, the element is supposed to move with the scroll position of the body if relativeToWrapper is set to true