Digging into Defold’s position APIs and physics timing nuances

Questions
1

I’ve learned that unlike get_position(), get_world_position() returns the value of the position from the previous frame:

It’s good that this is documented, but there are some nuances that aren’t documented that are important if you’re doing precise fixed-timestep physics. If anyone could answer these, it would prevent me having to run a bunch of experiments! I volunteer to open a PR to capture these answers, if anyone already knows:

  1. At which component lifecycle hooks, if any, should I expect get_world_position to match get_position for a moving object? Or will get_world_position universally return data that is at least 1-frame stale?

  2. What is meant by “frame” in the docs? Is it a physics frame, or a render frame? ie in update, is get_world_position reliably 1-frame delayed? In fixed_update is it unknown N-frames delayed?

  3. For a given object in a single frame, which is called first, fixed_update or update?

  4. For other API functions, like physics.raycast(), that take world coordinates as input and return them as output, what state of the physics world are they working with? Will a raycast hit or miss an object that was moved into its path just in the last frame? When it returns a world hit.position, does that point reflect the current get_position() of the object, or the get_world_position() of last frame, or is the answer unreliable?

  5. Is there any mechanism of ordering physics? I’ve learned that for certain very limited situations, if I want say a single type of game objects (like players), to update after the rest of the world has updated, I can msg.post("#", "deferred_fixed_update") and handle the message myself. However, I don’t know if this means that multiple “deferred_fixed_update” messages will be queued up and passed in the “message delivery” part of the lifecycle if for instance a frame fit multiple physics ticks within it (imagine a 120Hz physics game running on a 60Hz monitor), and if they’d still be in order.

Cheers!

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