flecs-zig-ble/README.md

# flecs-zig-ble

.. is a [Zig] wrapper around [Flecs], the powerful and fast Entity Component System library. It provides higher-level abstractions around Flecs' primitives and uses Zig's meta-programming functionality for more easily readable and maintainable code.

This library is still very much work-in-progress and not ready for use. It's available for people to have a look, give feedback and take inspirations. I'm attempting to develop this project using a test-driven development approach, translating Flecs' C tests (and later, examples) to Zig, creating wrapper types and functions as I go.

[Zig]: https://ziglang.org/
[Flecs]: https://github.com/SanderMertens/flecs

## Example

```zig
const std = @import("std");

const flecs = @import("flecs-zig-ble");
const Context = flecs.Context(void);
const World = Context.World;
const Iter = Context.Iter;

const Position = struct { x: f32, y: f32 };
const Velocity = struct { x: f32, y: f32 };

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    flecs.init(gpa.allocator());

    const world = try World.init();
    defer world.deinit();

    // Register components.
    _ = try world.component(Position);
    _ = try world.component(Velocity);

    // Register a system that moves any entity that has a `Position` by `Velocity` each update.
    _ = try world.system("Move", move, flecs.c.EcsOnUpdate, "Position, [in] Velocity");

    // Create an entity with both `Position` and `Velocity` already pre-added.
    const e = try world.entity(.{ .name = "Wroom" }, .{ Position, Velocity });
    // However the components aren't initialized, so do that here:
    e.set(Position, .{ .x = 10, .y = 20 });
    e.set(Velocity, .{ .x = 1, .y = 2 });

    // Progress the world, updating it forever.
    while (world.progress(0.0)) {  }
}

fn move(it: Iter) void {
    // Entities that share components are stored in the same table.
    // This function will be called for each table that matches the query.
    // With `field` we can grab a column from this table as a typed slice.
    const pos_col = it.field(Position, 1);
    const vel_col = it.field(Velocity, 2);

    // Both columns have the same size, so we can iterate them at the same time.
    // Since we want to modify `Position` we can get a pointer to the element.
    for (pos_col, vel_col) |*pos, vel| {
        pos.x += vel.x * it.deltaTime();
        pos.y += vel.y * it.deltaTime();
    }
}
```