197 lines
9.5 KiB
Markdown
197 lines
9.5 KiB
Markdown
## JGR's Patchpack: Low level changes
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This document describes low-level changes to the codebase which are not generally visible when actually running/playing the game, this is a non-exhaustive list.
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This document does not describe the player-visible changes/additions described in the main readme.
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### Crash logger and diagnostics
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* Additional logged items: current company ID, map size, configure invocation, thread name, recently executed commands, static NewGRFs.
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* Additional logged platform-specific items: detailed OS version (Unix), signal details (Unix, Mac), exception record data (Windows).
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* Better handling of crashes which occur in a non-main thread (ask the main thread to do the crash screenshot and savegame).
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* Support logging register values on Unix and Mac.
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* Support using libbfd for symbol lookup and line numbers (gcc/clang).
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* Support using gdb/lldb if available to add further detail to the crashlog (Unix, Mac).
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* Support using sigaction and sigaltstack for more information and correct handling of stack overflow crashes (Unix).
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* Attempt to log stack overflow and heap corruption exceptions (Windows).
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* Demangle C++ symbols (Unix).
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* Attempt to handle crashes which occur within the crashlog handler, by skipping or only partially writing the faulting section.
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* Emit a "crash" log, savegame and screenshot on multiplayer desync.
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* Add crash/desync information to output screenshot and savegame files.
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* Multiplayer server and client exchange desync logs after a desync occurs.
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* Multiplayer clients send state hashes and random values since the last sync to the server after a desync, to identify which frame first diverged.
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* Decrease sync frame period when desync occurs.
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#### Assertions
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* Various assertions are extended to log further information on failure.
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* Various assertions which check the state of a tile are extended to dump the tile state (m1 - m8, etc.) on failure.
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#### Scope annotations
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* Scopes (in the main thread) can be annotated with a functor/lambda which is called in the event of a crash to provide further information to add to the crash log.
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#### NewGRF debug window
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* Add various supplementary non-GRF information, e.g. vehicle variables and flags.
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* Add NewGRF sprite group dumping and related functionality.
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#### Logging
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* Add yapfdesync, linkgraph, sound, and command log levels.
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* Extend desync and random logging.
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### Map
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* Store tunnel start/end pairs in a pool, indexed in the start/end tiles.
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* Set bit in map if level crossing is possibly occupied by a road vehicle.
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* Cache inferred one-way state of road tiles.
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* De-virtualise calls to AnimateTile().
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* Cache animated tile speed.
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* Cache whether water tiles have water for all neighbouring tiles.
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* Improve performance of arctic snow line checks.
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### Viewport
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* Cache bridge/tunnel start and ends.
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* Cache station sign bounds.
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* Split sprite sort regions when more than 60 sprites present.
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* Reduce unnecessary region redraws when scrolling viewports.
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* Reduce viewport invalidation region size of track reservation and signal state changes.
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* Cache landscape background in map mode.
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* Partial parallelisation of non-map mode viewport rendering.
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### Rendering
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* Track dirty viewport areas seperately from general screen redraws, using a zoom-level dependant sized grid.
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* Use a rectangle array for general screen redraws instead of a block grid.
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* Add a dirty bit to windows and widgets, for redrawing entire windows or widgets.
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* Clip drawing of window widgets which are not in the redraw area.
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* Reduce unnecessary status bar and vehicle list window redraws.
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* Filter out tile parts which are entirely outside the drawing area, within DrawTileProc handlers.
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* Improve performance of drawing rail catenary.
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* Cache which window types are currently shown.
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### Data structures
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* Various data structures have been replaced with B-tree maps/sets (cpp-btree library), or robin-hood hash maps.
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* Various lists have been replaced with vectors, or other data structures.
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* Various deques and queues have been replaced with ring buffers.
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* Remove mutexes from SmallStack, only used from the main thread.
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* Add a third parameter p3, and an auxiliary data mechanism to DoCommand/CommandContainer.
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* Add a free bitmap for pool slots.
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* Maintain free list for text effect entries.
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* Many fields have been widened.
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* Change underlying data structures for ScriptList, create reverse mapping on demand instead of unconditionally.
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* Split GoodsEntry structure.
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### Vehicles
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* Cache the sprite_seq bounds.
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* Index the order list in a vector.
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* Observe the operation of the NewGRF when getting the vehicle image/sprite, and elide further calls to the NewGRF if it can be determined that the result will be the same.
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* Update train/road vehicle image/sprite on demand (i.e. when on screen) when image is continuously updated by GRF.
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* Add consist flag for the case where no vehicles in consist are on a slope.
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* Add vehicle flag to mark the last vehicle in a consist with a visual effect.
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* Index the vehicle list in per type arrays for use by CallVehicleTicks.
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* Cache whether the vehicle should be drawn.
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* Pre-compute engine refit capacity callbacks if possible.
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### Network/multiplayer
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* Add supplementary information to find server UDP packets and reply in an extended format with more info/wider fields if detected.
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* Paginate UDP packets longer than the MTU across multiple packets.
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* Use larger "packets" where useful in TCP connections.
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* Send vehicle caches from network server to clients to avoid desyncs caused by non-deterministic NewGRFs.
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* Change network protocol to send server/join and rcon passwords in an encrypted form (key exchange) instead of in clear text.
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* Encrypt the contents of rcon messages to the server and any responses.
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### Sprites/blitter
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* Add a fast path to Blitter_32bppAnim::Draw.
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* Replace sprite cache implementation.
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* Only cache sprites at the currently required zoom levels instead of all of them.
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* Add brightness adjusting modes to non-8bpp blitters.
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### Link graph
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* Completely change link graph job scheduling to make the duration of a job and the number of jobs per thread instance variable according to the estimated size of the job.
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* Various use of custom allocators, etc.
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* Early abort link graph threads if abandoning/quitting the game.
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* Various forms of caching and incremental updates to the link graph overlay.
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* Change FlowStat from an RB-tree to a flat map with small-object optimisation.
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* Change FlowStatMap from an RB-tree to a B-tree indexed vector.
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* Change LinkGraph::EdgeMatrix to a sparse storage format.
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* Replace MCF Dijkstra RB-tree with B-tree.
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* Reduce performance issues when deleting stale links with refit to any cargo.
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* Dynamically adjust accuracy parameters in MCF 1st pass to avoid computing large numbers of excessively small flows.
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### Pathfinder
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* YAPF: Reduce need to scan open list queue when moving best node to closed list
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### Save and load
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* Feature versioning, see readme and code.
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* Extend gamelog to not truncate version strings.
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* Save/load the map in a single chunk, such that it can be saved/loaded in one pass.
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* Various other changes to savegame format and settings handling, see readme and code for details.
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* Replace read/write accessors and buffering.
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* Perform savegame decompression in a separate thread.
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* Pre-filter SaveLoad descriptor arrays for current version/mode, for chunks with many objects.
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* Support zstd compression for autosaves and network joins.
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### AI/GS
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* [AI/GS script additions](docs/script-additions.html).
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* Add AI/GS method to get current day length.
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* Add GS method to create river tiles.
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* Add AI/GS methods related to road and tram types.
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* Add workaround for performance issues when attempting to create a town when no town names are left.
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* Fixup a GS otherwise inconsistent with day length.
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### NewGRF
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* [NewGRF specification additions](docs/newgrf-additions.html).
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* Add workaround for a known buggy NewGRF to avoid desync issues.
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* Apply many optimisations to VarAction2 deterministic sprite groups.
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* Avoid making callbacks which can be pre-determined to be unhandled, or which can be statically determined ahead of time.
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* Avoid animating industry tiles which are not actually animated in the current layout.
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* Setting the animation frame to its current value no longer triggers a redraw.
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* Animation is not started if it can be determined that it would stop immediately.
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* Avoid unnecessarily triggering or redrawing NewGRF houses.
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### SDL2
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* Update whole window surface if >= 80% needs updating.
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* Only pass a single rectangle to SDL_UpdateWindowSurfaceRects to prevent screen tearing.
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* Allow using the hash key (#) as a hotkey.
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### Other performance improvements
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* Use multiple threads for NewGRF scan MD5 calculations, on multi-CPU machines.
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* Avoid redundant re-scans for AI and game script files.
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* Avoid iterating vehicle list to release disaster vehicles if there are none.
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* Avoid quadratic behaviour in updating station nearby lists in RecomputeCatchmentForAll.
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### Command line
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* Add switch: -J, quit after N days.
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* Add savegame feature versions to output of -q.
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### Configure/build
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* Changes to gcc/clang detection and flags
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* Changes to version detection and the format of the version string.
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* Minor CMake changes.
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### Misc
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* Use of __builtin_expect, byte-swap builtins, overflow builtins, and various bitmath builtins.
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* Add various debug console commands.
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* Cache font heights.
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* Cache resolved names for stations, towns and industries.
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* Change inheritance model of class Window to keep UndefinedBehaviorSanitizer happy.
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* Various other misc changes and fixes to reduce UndefinedBehaviorSanitizer and ThreadSanitizer spam.
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* Add a chicken bits setting, just in case.
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