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https://github.com/ggabriel96/lasso

A generic game loop implementation in C++
https://github.com/ggabriel96/lasso

cpp game-development game-loop

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A generic game loop implementation in C++

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README 

        
# lasso



A generic game loop implementation in C++ based on

[Fix Your Timestep!](https://gafferongames.com/post/fix_your_timestep/)



lasso is at early stages of design and development and is subject to

incompatible changes. All feedback is welcome and appreciated!

Detailed documentation is being built on the

[wiki](https://github.com/ggabriel96/lasso/wiki).



# Getting started



This project supports the [Meson](https://mesonbuild.com/) build system,

so you may want to install it (although it is not required). A legacy

[`CMakeLists.txt`](CMakeLists.txt) still exists, but is not

*actively* maintained.

A compiler with

[Concepts TS](https://en.cppreference.com/w/cpp/experimental/constraints)

support (e.g. GCC 6 or above with options `-std=c++2a` and `-fconcepts`)

is required to use lasso. Then, having Meson installed,

run the following commands at the root of this project:



```sh

meson build

cd build && meson install

```



Alternatively, you may just put [`lasso.h`](include/lasso.h) somewhere in

the source tree of your project.



## Using lasso



The `meson install` command above will put (install) it at `/{prefix}/lasso/`

(relative to the default Meson

[paths](https://mesonbuild.com/Builtin-options.html)).

On Linux, that is `/usr/local/include/lasso/`.

Then you just need to have `/usr/local/include/` in your header search path

and you are ready to `#include `.

Conversely, if you have somehow put [`lasso.h`](include/lasso.h) in your

source tree, you need to `#include "lasso.h"`.



lasso knows how to call into your game via the C++ concept below:



```cpp

template concept bool GameLogic =

requires (T logic,

          LoopStatus const &status,

          duration const &delta) {

    { logic.init() } -> void;

    { logic.simulate(status, delta) } -> void;

    { logic.render(status, delta) } -> void;

    { logic.is_done() } -> bool;

    { logic.terminate() } -> void;

};

```



That means you need a `class` or `struct` that implements the

following member functions:



- `void init();`, which is called once right before the loop starts and you

  can use it to initialize anything you need (beyond the constructor of your

  class);

- `void simulate(LoopStatus const &, duration const &);`,

  which is called if `delta` or more nanoseconds have passed since the last

  call to advance your simulation (input, physics, AI, etc.);

- `void render(LoopStatus const &, duration const &);`,

  which is called once in every iteration to render what has been simulated;

- `bool is_done();`, which is called once in every iteration to

  determine whether the loop should terminate;

- `void terminate();`, which is called once right after the loop ends and you

  can use it to clean up anything you need (additionally to what will be

  done in the destructor of your class).



Additional member functions may be added to GameLogic

and its existing ones might be modified in the future.

There are no constraints on other member functions or

variables that the class may have.

Examples of classes implementing this concept can be seen in the

[examples folder](examples/), especially the [`Game.h`](examples/Game.h).

and [`Game.cpp`](examples/Game.cpp) blueprints.



After having implemented your class (let us call it `T`),

running it is as simple as:



```cpp

T t;

// ...

lasso::MainLoop{}.run(t); // or pass in T{} directly

```



## Building the examples



The [Simple and Fast Multimedia Library (SFML)](https://github.com/SFML/SFML)

must be installed to compile and run an [example](examples/).

If you want to enable the compilation of the examples, you may run:



```sh

meson build -Dexamples=true

cd build && ninja

```



or, after having initially run Meson and while at the `build/` directory:



```sh

meson configure -Dexamples=true

ninja

```



In order for an example to locate [`Roboto-Regular.ttf`](examples/data/fonts/)

and hence render text, you must run the compiled executable from either the

build or the [`examples/`](examples/) directory (or set any of them as the

working directory in your IDE; preferably the build one).