Swiping a direction="vertical" Scene down only by its header or custom component

[jacenko]

Version

Tell us which versions you are using:

• react-native-router-flux v3.37.0
• react-native v0.40.0

Expected behaviour

There should be a way to turn on the ability to swipe a modal down only by its header or specific custom component while ignoring modal swipe gestures on the content itself. This will be ideal behavior when there is a ScrollView in the Scene, for example.

Actual behaviour

When you are in a modal Scene (direction="vertical") that has a ScrollView, using panHandlers={null} on the Scene allows the ScrollView to be used without bugs, but swiping the header down doesn't do anything.

Alternatively, not using panHandlers={null} on the Scene makes the whole Scene movable, but creates unexpected behavior if there's a ScrollView within the Scene. In this scenario, only moving the ScrollView slowly works. Flicking down the ScrollView dismisses the Scene. Flicking it up just freezes the ScrollView for a second.

Steps to reproduce

1. Create a second Scene with direction="vertical" and panHandlers={null} and add a ScrollView with a bunch of items to its component.
2. Go to this scene using Actions.key, for example.
3. Try to swipe/flick the ScrollView (should work). Swiping the header down won't do anything.
4. Remove panHandlers={null} from the Scene and go to it again.
5. You can swipe the modal by its header to dismiss but the ScrollView will be wonky as described above.

[getnashty]

this is a huge problem, we should be able to control edgeHitWidth