Porting ue4-dev improvements to ue5-dev

[youtalk]

Motivation

The ue4-dev branch has accumulated a significant number of bug fixes, feature additions, and improvements over the past several releases that have not been ported to ue5-dev. Since ue5-dev is the future of the project, these gaps leave users on the newer branch without fixes and features that are already available in ue4-dev.

Rather than cherry-picking commits (which often fail due to the UE4→UE5 structural differences), I propose implementing equivalent functionality as new code targeting ue5-dev directly, submitted as a series of focused, independently reviewable PRs.

Proposed PR series

The changes are organized into 21 PRs across 9 categories. Each PR is self-contained and can be reviewed and merged independently.

Category 1: Bug fixes (small PRs, ready for immediate merge)

PR	Title	Changes	Reference commits (ue4-dev)
#0a	fix(LibCarla): core bug fixes	RPC deadlock (atomic_bool), assert removal, OpenDrive lane width, GeoReferenceParser crash, TM NaN error, yield→sleep_for, assert relaxation	0c477d65c, 7b2ef1d94, 3b3b890ae, 280c71c42, 488fd42a4, 4c49a741d, 5161fb09e
#0b	fix(streaming): restore ROS 2 sensor data flow	Fix ROS 2 sensor data stopping when no Python client is connected	6bf5e3d94
#0c	fix(sensors): camera fx, semantic tags, pedestrian bbox	Camera fx calculation, actor semantic tags, large map tag IDs, pedestrian bounding box, Environment Object API, camera frame/timestamp	86ebadcee, 40ac1f19e, ff009c8a3, ccc86c6b4, 742113a92, 86a1ec101, a095219c7
#0d	fix(LibCarla): eliminate compiler warnings	Fix ~282 compiler warnings (integer truncation, NRVO inhibition, C-style casts, etc.)	d179041f4

Category 2: ROS 2 enhancements

PR	Title	Changes	Reference commits (ue4-dev)
#0e	feat(ros2): transformation fix and refactor	ROS 2 transformation calculation fixes, degree→radian conversion, multi-GPU actor destruction fix, dependency compilation fix	a46b2690b, cd3d640f3, 201d375d3, a6f6ed03d
#0f	feat(ros2): geometry data types and multistream support	Updated geometry data types (28 files), multistream preparation (67 files)	590d54f02, 3b938d718
#0g	feat(ros2): V2X sensor and serializer	V2X sensor (28 files), serializer/RPC (90 files)	8f33324d9, 1146277a7
#0h	feat(ros2): fine-grained server synchronization	Per-client independent synchronization (14 files)	aa9c92b21

Category 3: Recorder and replay

PR	Title	Changes	Reference commits (ue4-dev)
#0i	feat(recorder): weather recording and simultaneous record/replay	Weather recorder support, simultaneous record/replay, stop_replayer flag, map_override argument, spectator attach to signals	df0161e87, be60694b7, 5ab7c76ea, 70bee19db, fd6c4e0bf
#0j	fix(recorder): replay compatibility fixes	0.9.15 log file replay, door animation crash/hang, sample replayer fix	c9f2e3ab6, 7b0707548, 969f9ce20

Category 4: TrafficManager

PR	Title	Changes	Reference commits (ue4-dev)
#0k	feat(tm): improved large vehicles and PID tuning	Large vehicle intersection behavior, angle-based PID, null access segfault fix, mutex removal, vehicle reuse aliasing	4fdea38a5, c8dfee97e, fb5f61269, e7e076f1b, 141fc20ae

Category 5: Vehicle, physics, and control API

PR	Title	Changes	Reference commits (ue4-dev)
#0l	feat(vehicle): wheel rotation API and telemetry	Wheel pitch rotation API, server-side processing, telemetry data, WheelTelemetryData Python conversion, physics-off GetVehiclePhysicsControl, wheel check when physics disabled, COM height adjustment	a14b2d943, 03e71c251, 01b1ede51, 3647beaf0, fda970b88, e7e3987f7, bd6860437
#0m	feat(api): new force/impulse and actor component functions	Position-specified force/impulse, actor component getters, bone transform retrieval, socket name retrieval, debug shape clear, GeoLocation→Transform conversion, custom path map loading	60fdd57e0, 0b13c72d6, 5d6862c3d, 3eb9a7626, 00ff27ac3, 5ca6323f4, 842f44294

Category 6: New sensors

PR	Title	Changes	Reference commits (ue4-dev)
#0n	feat(sensor): fisheye camera (Kannala-Brandt model)	Fisheye camera (32 files), Normals camera fisheye variant	390aa0b8e, 8f6e2b348
#0o	feat(sensor): hybrid solid-state LiDAR	Hybrid solid-state LiDAR	a4eca2e4d
#0p	feat(sensor): IMU gravity parameter and geolocation	IMU gravity parameter, geo projection, GNSS UTM projection	caca5f02e, 39f7741b7, 9ce853e99

Category 7: Segmentation

PR	Title	Changes	Reference commits (ue4-dev)
#0q	feat(segmentation): masked materials and instance segmentation fixes	Masked material instance segmentation, mesh segmentation appearance bug, instance segmentation improvements, terrain invisibility fix, spline mesh invisibility fix, translucent material segmentation	8b79b708e, 9c620141f, e8947a47c, d859cd9d2, f45dd6943, 4da825b42

Category 8: Left-hand traffic

PR	Title	Changes	Reference commits (ue4-dev)
#0r	feat(map): left-hand traffic support	Full LHT support (maps, lanes, signals, TrafficManager)	77894abcd

Category 9: Other improvements

PR	Title	Changes	Reference commits (ue4-dev)
#0s	feat(opendrive): lane marking and waypoint fixes	Lane marking/tree generation, reverse connection waypoint fix, Lane.GetLaneCorners crash fix, xml_node null pointer checks, OpenDriveActor custom path	86fcfe5e8, e41ffa03c, 4d4dd1d11, 4ca87e818, 6cb77140c, 58c870ae3
#0t	feat(traffic): traffic light and sign improvements	Floating signal fix, sign height adjustment refactor, underground trigger box fix, OpenDRIVE-based signal trigger volume fix, BoxComponent for sign height	f856729ee, e06993189, c1ba7342c, 2fed7136e, 363da3d78
#0u	feat(python): agent improvements and InvertedAI	Agent code typing/modernization, BasicAgent set_destination improvement, InvertedAI QoL improvements, InvertedAI script, obstacle detection fix (empty list), carla.command import fix	9a59963ca, 4da0c7415, 29af5dc89, b60034be6, 694ad122a, aeeff9907

Submission order

All PRs within each week are independent and can be reviewed in parallel.

PRs	Focus
#0a, #0b, #0c, #0s	Bug fixes — small, immediately mergeable
#0d, #0k, #0l, #0t	Compiler warnings, TrafficManager, vehicle API, traffic signs
#0i, #0j, #0m, #0q	Recorder, API extensions, segmentation
#0e, #0u, #0p	ROS 2 transformation fixes, Python agents, IMU/GNSS
#0f, #0g, #0h, #0n, #0o, #0r	Larger features: ROS 2 multistream, V2X, fisheye camera, solid-state LiDAR, left-hand traffic

The Week 1 PRs are intentionally the smallest and most straightforward — pure bug fixes that should be uncontroversial and quick to review. This establishes the pattern and builds momentum for the larger PRs.

Approach

For each PR, I am implementing equivalent functionality as new code targeting ue5-dev rather than cherry-picking from ue4-dev. The reference commits listed above are used to understand what needs to change, but the actual implementation accounts for UE5.5 API differences and the current state of ue5-dev.

Questions for maintainers

1. Granularity: Are 21 PRs too many, or is this level of granularity helpful for review? I can split or merge PRs based on your preference.
2. Priority: Are there specific categories you'd like to see first? I've ordered by estimated ease-of-merge, but if there are particular pain points on ue5-dev, I can reprioritize.

I'm happy to adjust the plan based on feedback. Looking forward to your thoughts.

[youtalk]

Tracking issue: #9635