AnimationEditor : Fix changing of frame by click & drag

[johnhaddon]

We mustn't edit the context returned by the ContextTracker - nobody is tracking it for changes, it is intended to be const, and other UI components might be using it in other threads. Instead we just use the ScriptNode context in the AnimationEditor as before.

This is the most minimal change needed to fix the bug. You could argue the case for making the AnimationEditor genuinely focus-aware by accounting for TimeWarps between the node being viewed and the node being edited. That would require a lot of work though, and it's not clear that it's worth it, or that it can be done without an ABI break.

[murraystevenson]

Thanks! I can confirm that this fixes the aforementioned bug, but unfortunately it exposes another. The AnimationGadget was reliant on the now removed setContext() call to dirty itself for rendering when the context changed, so it now doesn't update when the frame is changed on the playback slider unless you dirty it another way, such as by madly waving the mouse over the gadget during playback...

[johnhaddon]

it now doesn't update when the frame is changed on the playback slider

Doh! Thanks for catching that. I've pushed another version which should fix both the old and the new problem. I've also added some notes about how we should do this better - we can't currently do that easily because it would mean adding a member to AnimationGadget, which would cause an ABI break.

[murraystevenson]

Thanks for the todo! This looks good to merge after a rebase to fix the Changes.md conflict.