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Gdnim

gdnim is a testbed for experimental features for godot-nim projects that implements hot reloading of dlls as well as features for ease of development.

NOTE A new macro gdnim was added to replace gdobj for defining classes. See the gdobj branch for the old samples.

Why?

The goal is to streamline and speed up the process of development for godot-nim by adding experimental features like:

  • support for Nim 2.0 ARC/ORC
  • hot reloading
  • match gdscript features, e.g.: signal declarations, async signal handling, field accessors
  • reducing boilerplate, error proneness:
    • file watcher recompiles on save
    • generation of files for scripts and editor plugins (.nim, .gdns, .tscn, etc)
    • generated Godot API includes exports for referenced classes. For example you don't need to import godotapi / [scene_tree] on node since node exports scene_tree, unless you want autocompletion from nimsuggest.
    • automatic nil'ing Godot types on exit_tree to stop console warnings. e.g.: self.myResource = nil in exit_tree is defined automatically.

Quick Setup Guide

  • Compile the build script: nim c build
  • Configure the build.ini with the location of godot bin files. If you have your own build of godot you can configure the repo source directory and use ./build gdengine
  • See available tasks: ./build help
  • Download Nim prerequisite libraries and generate the godot-nim bindings: ./build prereqs
  • Build watcher and components: ./build cleanbuild

For a new project (sample code removed), branching from master: ./build init [branch_name]

Quick Dev Guide

  • To make a new nim component run: ./build gencomp my_comp node_2d. The nim file is created for you in components See Setup for details.
  • Edit as needed components/my_comp.nim
  • Build the component: ./build -m (-m moves the safe dll to the hot dll path)
  • Launch godot editor with: ./build gd (if this fails, launch godot manually, or see the Setup section)
  • Open, edit (as needed) and play the generated component scene file: _tscn/my_comp.tscn
  • Start the component file watcher for recompilation ./build cwatch
  • Make a modification to component, the component watcher will rebuild the component.
  • Hot reload should occur if there were no compiler errors.

Prerequisites

Component Setup

Create a component by running ./build gencomp [name] [godot_class]. name is the name of your component, and godot_class is the class from which it derives. Both should be in snake_case.

For example ./build gencomp my_node node_2d generates a my_node.nim file in /components. And a matching tscn, gdns, and gdnlib file in the directories specified in build.ini.

To delete a component run: ./build delcomp [name].

New components are generated from template strings defined in tasks.nim. Customize it for your needs. Remember to recompile ./build with nim c build with any change to tasks.nim.

Hot Reloading Setup

The gdnim macro is a layer over godot-nim's gdobj macro that interacts with the Watcher to enable hot reloading. There are four sections to consider when setting up for hot reloading.

  • first: Takes a body of code that is only run during initialization. It executes at the top of enter_tree.
  • dependencies: Declares other components as dependencies. If a component instance holds a reference to other component instances, but their relationship is not declared in dependencies hot reloading will fail when the dependency needs to reload. By declaring dependencies, when the dependency reloads the dependent component will reload with it. See the example components color_palette and color_palette_slot.
  • unload: Used to perform data serialization for data that can't be saved as a {.gdExport.}. Call the save() macro to store the data with Watcher.
  • reload: Declares that the component is hot reloadable. This takes a body of code that is run at the top of enter_tree, but after first. Call the load() macro to retrieve any data stored with Watcher via save().

You can choose not to define the enter_tree method and put its code inside the reload: section.

Hot Reloading Checks

The proc isNewInstance() can be used to check the reloading state of a component instance at runtime. This is useful for initialization or adding children dynamically.

You can do conditional compilation for reloading code with when defined(does_reload):, but this currently, only works inside methods. It would require a modification to gdobj to work in general.

Hot Reloading Switch

A top level gdnim macro is implemented to replace the use of gdobj. See below for implementation details

  • Hot reloading makes use of components as sub-scenes. A component is a unit that has a .tscn scene file, with the root node containing the .gdns nativescript attached, pointing to the .nim code file generated dynamic library. The correct setup for reloading is a hierarchy of scenes. See /app/scenes/main.tscn and how it references the other component scenes from /app/_tscn.
  • In the autoload settings, the Watcher scene is loaded which monitors the /app/_dlls folder for changes.
  • Setup a component properly for reloading, use the gdnim macro to define your class.

See components for samples on how to set things up for reloading.

  • Disable hot reloading This will stop compilation of the Watcher, delete the Watcher files, and disable the reloading parts of the components.

    • Edit build.ini, under [Hot], set reload="off".
    • Do a clean build. ./build cleanbuild
    • Modify project.godot Autoload so the Watcher isn't loaded. You can go through the Project settings or modify project.godot directly.

  • Re-enable hot reloading

    • Edit build.ini, under [Hot], set reload="on".
    • Do a clean build. ./build cleanbuild
    • Modify project.godot Autoload so the Watcher is loaded. Select _tscn/watcher.tscn to load.

Tips

  • Flags used with ./build
    • By default, builds any modified component .nim for hot reload.
    • ./build comp compName is the same as ./build compName. Only component compName is built.
    • ./build will build all changed components for hot reloading.
    • -m or --move: ./build -m builds and moves the dll from the safe to hot path. Use when the game is closed to prevent Watcher from reloading on start.
    • -f or --force: ./build -f force builds the components.
    • --ini:custom_build.ini: pass in your own ini file for different build configurations.
  • If the godot app crashes, or your component gets into a weird state where it can't reload cleanly. Close the app and run ./build -m to move the safe dll to the hot dll path and rerun the app.
  • If the app is crashing when trying to reload, try force rebuilding the component ./build -f comp_name or deleting the dll and rebuilding.
  • If all else fails, ./build cleanbuild to rebuild the dlls from scratch.

Debugging Crashes

  • On Windows you can get a stacktrace of a crash if you use vcc as the compiler and set the build_kind to debug.
  • If you get some type of crash when running your game, you probably have a NilAccess error in your code. Using the ifValid macro in utils you can wrap your code in a nil check, and it'll print to the console if a nil access is detected. You can do toggle the output with build.ini's verbose_nil_check.
  • Another cause of crashes could be from calling Godot's virtual functions by accident. For example, you might try calling get or get_property_list. This might cause a crash because _get and _get_property_list are virtual functions in Godot. In godot-nim, Godot's _get is mapped to godot-nim's method get, and Godot's get is mapped to godot-nim's getImpl. See deps/godotapi/objects.nim for examples.

Sample Projects

Project Structure

Gdnim uses a customized build script and godot engine 3.x which unloads gdnative libraries when their resource is no longer referenced. It removes the dependency on nake and nimscript, but requires you to recompile build.nim if you change build.nim or tasks.nim. Gdnim also uses a custom version of the godot-nim bindings in the deps/godot directory.

Files and Folders

  • You can customize the location of folders in build.ini.
  • app: This is the godot project folder.
    • app/_dlls: Location for ./build compiled, component libraries (.dll's, .so's). If you have other dlls you want to store here, modify tasks.nim. See task cleandll, or put your dlls somewhere else.
    • app/_gdns: Location for ./build gencomp generated NativeScript files. These are checked and regenerated for each component nim file. So they're safe to delete when you want to remove a component.
    • app/_tscn: Location for ./build gencomp generated tscn files. Customize these for your needs.
    • app/scenes: (Optional) Location for your own scenes to keep separate from _tscn.
  • deps/app: A blank godot project used when creating a new project with ./build init.
  • deps/godot: Custom version of godot-nim bindings. You can move this and update the location in build.ini
  • deps/tcc: tcc header required on Windows for asyncdispatch
  • deps/watcher: scene files for Watcher. When reload is re-enabled, the Watcher scene files are copied from here to app.
  • build.nim: The build script, compiled with nim c build, includes the tasks.nim
  • tasks.nim: Build tasks are specified here for updating / compiling the godot engine, generating / compiling components, running the godot editor, etc. You can modify the templates used to generate component files up top. After modifying rebuild with nim c build.
  • gdnim/watcher.nim: The Watcher node that monitors changes to registered components. In a new godot project set _tscn/watcher.tscn to autoload in Project Settings.
  • gdnim/gdnim.nim: Included in every component, imports and exports godot-nim and stuff below.
    • gdnim/globals.nim: Defines constants and symbols used for hot reloading and Watcher signals.
    • gdnim/hot.nim: The module implements the gdnim, save, load and other macros to make interacting with Watcher and hot reloading easier.
    • gdnim/utils.nim: This module contains helper procs and macros.
  • build.ini: The default configuration file used to specify directories and settings. This is read when ./build is run. A different config file can be set using the --ini flag. Example: ./build --ini:my_config.ini cleanbuild
  • components: Where .nim component files live. Components must have unique identifiers across the project. Dlls are generated from these components.
  • components/tools: Where nim files for tool / editor plugins go. Generated with ./build gentool my_tool_name
    • WARNING: GDNative reloading of tool scripts is broken. If you enable and disable the plugin, or unfocus the editor window while the plugin is enabled which will cause the plugin to reload, you might get a crash. You also might get warnings about leaked resources, when the plugin is enabled while the editor is closed. As a workaround, gdnlib's reloadable flag is set to false, so the plugin will not reload when the editor is unfocused. To see your changes, close the editor and reopen after compilation.

Project Setup

Modify the build.ini, build.nim and tasks.nim script for your needs. build.ini expects some paths the godot engine repo and editor executables.

If you're not interested in building godot from source, you can use Godot 3.x and ignore the ./build gdengine command. If you want to use ./build gd or ./build play to launch the editor or app fill out the paths to your editor binaries.

The rest of the settings under build.ini's [Godot] section are for building godot from source. If you have all my mods from build.ini's merge_branches in your git repo you can, run ./build gdengine update. Otherwise stick to using godot engine 3.x.

The app folder contains the godot project. You can use ./build init branch_name to create a new gdnim project on a new branch.

You create "components" which are the classes that can reload by running the ./build gencomp your_module_name godot_base_class_name. A nim file will appear in the components folder. Generated files are stored in app/_dlls, app/_gdns, app/_tscn.

See the examples in the components folder.

See ./build help for available tasks like downloading the godot source, compiling the engine, generating godot-nim bindings api, compiling the watcher and components, etc.

./build gd Launches the godot editor. On Windows it spawns a terminal using Terminal. On Linux there isn't a general way to support launching the editor from a terminal for all distributions (as far as I know), so modify the task gd for your system.

Tasks

xxx The build system consists of build.nim, tasks.nim, build.nim.cfg and build.ini. build.nim includes tasks.nim and reads build.ini at runtime. To compile the build system run: nim c build.

Tasks are defined in tasks.nim. You can customize it for your needs, just make sure to recompile. Changes to build.ini are picked up when ./build executes. Find out what tasks are available by inspecting that file or running ./build help

By default running ./build will build any components that have changed. If you supply an argument with no task name: ./build my_comp the argument is assumed to be a component.

Implementation details

Watcher monitors the app/_dlls folder for updates and coordinates the reload process with the components. The components use the hot module save and load macros to persist data with Watcher.

NOTE Below details how to hot reloading works when using the gdobj macro. Using the gdnim macro reduces the boilerplate for the setup, and does all this stuff for you. See the gdobj branch components for samples.

To set up a component for reloading, the component needs to:

  • Call hot.register_instance which registers the component name with the Watcher node. Typically, done when godot's Node.enter_tree() runs, so the component can find the Watcher. The gdnim macro defines this if you have a reload: section.
  • To persist data between reloads Watcher uses PackedScenes and calls proc hot_unload(): seq[byte] {.gdExport.} on the Node to serialize custom data. The gdnim macro defines hot_unload with the unload: section.
  • Inside hot_unload the hot.save() macro is used to specify member fields to save.
  • To reload custom data, after registering you can call the hot.load macro like register_instance(comp)?.load(self.data). Watcher will return previously persisted data after a component is registered so the node can complete initialization.
  • Components can be independently hot reloaded as long as they don't share an ascendant/descendant relationship in the scene hierarchy. If a component A has another component B as a descendant, a dependency needs to be defined between the components.

When a component is compiled it generates a library file (safe dll). If the godot editor is not in focus with the project opened the safe dll can be copied to the hot dll path. Otherwise, you'll get a warning that the dll can't be moved and reload will fail.

When the project application is running, update and build the components. Watcher will check if safe dll is newer than hot dll and start a reload if so.

Nim notes

The godot-nim library in deps has been customized to use the new gc:ORC and prep it for future versions of nim. This is why ORC is suitable for games: https://nim-lang.org/blog/2020/12/08/introducing-orc.html Use the build script to generate the godotapi into the deps folder. Gdnim, and the godot-nim bindings are tested against the nim devel branch 3b963a81.

Avoid the useMalloc option with ORC. It'll eventually cause a crash.

Compiler notes

  • GCC is the recommended compiler for most use cases. It supports all the features in gdnim, and is the middle of pack in terms of compilation speed.

    • Install gcc with scoop scoop. Gcc will be in your user's ~/scoop/apps/gcc directory.
    • Or use the latest builds for MinGW64 here: http://winlibs.com/.

    gcc requires some additional dlls in the _dlls folder to run. Using gcc on Windows, tasks.nim's final task checks for a couple dll's to support threading.

  • VCC is only available on Windows. It produces the smallest dlls, but has the longest compile times. Vcc + Visual Studio is useful for crash debugging purposes.

  • TCC Tiny C Compiler TCC has the fastest compile times, but crashes when compiling with threads:on. If compiling on windows, read deps/tcc/README.md to make tcc work with the asynchdispatch module. Tcc is not as well supported as the other compilers, and may not support all features of gdnim.

License

This project is licensed under the MIT license. Read LICENSE file for details.

Copyright (c) 2018 Xored Software, Inc.

Copyright (c) 2020 Don-Duong Quach

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godot-nim based bootstrapping framework supporting hot reloading

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