Fix: add world tracking on Apple Vision Pro for drawables to be visible

[okwasniewski]

This PR fixes the last issue with Apple Vision Pro rendering on a real device.

Note: While reviewing, look only at this commit: b83ca5e another one has already open PR (#3325)

Currently, when we don't attach the device anchor to the drawable (cp_drawable_set_device_anchor) the drawables are not presented on the device. To retrieve the device anchor we need to do following things:

1. Initalize a new world tracking provider:

ar_world_tracking_configuration_t config = ar_world_tracking_configuration_create();
world_tracking = ar_world_tracking_provider_create(config);

2. Start an AR session with this provider

  ar_session = ar_session_create();
  auto data_providers = ar_data_providers_create_with_data_providers((ar_data_provider_t)world_tracking, NULL);
  ar_session_run(ar_session, data_providers);

Important

This is API suggestion that unfortunately changes public-facing API, I'm open to another solution to make it work.

3. Pass world tracking provider to the bgfx::init:

init.platformData.worldTracking = entry::getWorldTracking();

4. Inside of bgfx we use this world tracking provider to get data about the headset position and set in on the drawable. This is a design decision issue that Apple made forcing us to mix rendering with retrieving device position.

Another possible solution is to run the ARSession inside BGFX, but this may limit the user's ability to run other providers like Hand Tracking Provider, etc.

You can see a full integration into the bgfx examples here: okwasniewski@337474a (it first requires #3292 to be merged)

[okwasniewski]

Hey! I rebased the changes on the latest Apple Vision Pro PR.

[okwasniewski]

Hey @bkaradzic,

I've refactored the flow to start up ARSession inside of bgfx when running on AVP. This is the last bit that was required to fix rendering.

Here is a recording of the latest changes:

ScreenRecording_07-30-2024.12-37-56_1.MP4

(imgui may need some adjustments but overall it works good)

[bkaradzic]

Hey @okwasniewski I created visionOS channel on Discord so people interested in visionOS can discuss features and integration at one place. Please join here: https://discord.com/channels/712512073522872352/1267923444826112120