High-level wrapper around Flecs, a powerful ECS (Entity Component System) library, written in Zig language
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const std = @import("std");
const c = @import("./c.zig");
const meta = @import("./meta.zig");
pub fn Context(comptime ctx: anytype) type {
return struct {
pub const Entity = @import("./entity.zig").Entity(ctx);
pub const Id = @import("./id.zig").Id(ctx);
pub const Iter = @import("./iter.zig").Iter(ctx);
pub const Pair = @import("./pair.zig").Pair(ctx);
pub const World = @import("./world.zig").World(ctx);
/// Looks up an entity ID unique to this `Context` for the provided
/// type that has been registered previously, typically done by
/// calling functions such as `World.component(...)`.
pub fn lookup(comptime T: type) c.ecs_entity_t {
const result = lookupMut(T).*;
if (result == 0) std.debug.panic("No lookup for {s}", .{@typeName(T)});
return result;
}
/// Returns a pointer unique to this `Context` and the provided type
/// that holds an entity ID. Useful for associating types to entities.
pub fn lookupMut(comptime T: type) *c.ecs_entity_t {
_ = T; // Only necessary to create a unique type.
const EntityHolder = struct {
pub var id: c.ecs_entity_t = 0;
};
return &EntityHolder.id;
}
/// Converts the specified value to an `ecs_entity_t`.
///
/// If `null` is passed to this function, either directly or through an
/// optional type of one of the supported types, `0` is returned. It's up to
/// the caller to do any necessary testing for `0` values, and whether the
/// returned entity is valid or alive.
///
/// The following can be converted:
/// - `Entity` and `ecs_entity_t` - Self-explanatory.
/// - `type` - Looks up the entity associated with that type.
pub fn anyToEntity(value: anytype) c.ecs_entity_t {
return switch (@TypeOf(value)) {
@TypeOf(null) => 0,
c.ecs_entity_t => value,
Entity => value.raw,
?Entity => if (value) |v| v.raw else 0,
type => lookup(value),
else => @compileError("Value of type " ++ @typeName(@TypeOf(value)) ++ " can't be converted to Entity"),
};
}
/// Converts the specified value to an `ecs_id_t`.
///
/// If `null` is passed to this function, either directly or through an
/// optional type of one of the supported types, `0` is returned. It's up to
/// the caller to do any necessary testing for `0` values, and whether the
/// returned id is valid.
///
/// The following can be converted:
/// - `Id` and `ecs_id_it` - Self-explanatory.
/// - `Entity` and `ecs_entity_t` - Self-explanatory.
/// - `Pair` - Converts to the equivalent `Id`.
/// - `.{ relation, target }` - A `Pair`, converted using `anyToEntity()`.
/// - `type` - Looks up the entity associated with that type.
pub fn anyToId(value: anytype) c.ecs_id_t {
const T = @TypeOf(value);
if (comptime meta.isTuple(T)) {
if (@typeInfo(T).Struct.fields.len != 2)
@compileError("Value of type " ++ @typeName(T) ++ " must be a tuple with 2 elements, to be a Pair");
const relation = anyToEntity(value[0]);
const target = anyToEntity(value[1]);
return c.ecs_make_pair(relation, target);
}
return switch (T) {
@TypeOf(null) => 0,
c.ecs_id_t => value,
Id => value.raw,
?Id => if (value) |v| v.raw else 0,
Pair => value.raw,
?Pair => if (value) |v| v.raw else 0,
// Technically same type as `ecs_id_it`.
// c.ecs_entity_t => value,
Entity => value.raw,
?Entity => if (value) |v| v.raw else 0,
type => lookup(value),
else => @compileError("Value of type " ++ @typeName(T) ++ " can't be converted to Id"),
};
}
/// Registers type lookups for the builtin Flecs entities.
/// These are defined in the `./src/builtin/` directory.
pub fn registerFlecsLookups(world: *World) !void {
const error_writer = std.io.getStdErr().writer();
const flecs = @import("./builtin/flecs.zig");
const root = try lookupAndRegister(world, null, "flecs", flecs, error_writer);
try lookupAndRegisterDeclarations(world, root, flecs, error_writer);
}
pub fn registerFlecsCoreLookups(world: *World) !void {
const error_writer = std.io.getStdErr().writer();
const flecs = @import("./builtin/flecs.zig");
const flecs_core = @import("./builtin/flecs.core.zig");
const root = try lookupAndRegister(world, null, "flecs", flecs, error_writer);
const core = try lookupAndRegister(world, root, "core", flecs_core, error_writer);
try lookupAndRegisterDeclarations(world, core, flecs_core, error_writer);
}
fn lookupAndRegister(
world: *World,
parent: ?Entity,
comptime name: []const u8,
comptime T: type,
error_writer: anytype,
) !Entity {
if (world.lookupChild(parent, name)) |entity| {
const id_ptr = lookupMut(T);
if (id_ptr.* != 0 and id_ptr.* != entity.raw) {
if (!meta.isNull(error_writer))
try std.fmt.format(error_writer, "Trying to register lookup for entity '{}' as {d}, but it's already registered as {d}\n", .{ entity, entity.raw, id_ptr.* });
return error.LookupIdMismatch;
}
id_ptr.* = entity.raw;
return entity;
} else {
if (!meta.isNull(error_writer)) {
if (parent) |p|
try std.fmt.format(error_writer, "Could not find child '{s}' of parent '{}'\n", .{ name, p })
else
try std.fmt.format(error_writer, "Could not find root entity '{s}'\n", .{name});
}
return error.EntityNotFound;
}
}
fn lookupAndRegisterDeclarations(
world: *World,
parent: Entity,
comptime T: type,
error_writer: anytype,
) !void {
inline for (@typeInfo(T).Struct.decls) |decl| {
const ChildType = @field(T, decl.name);
if (@TypeOf(ChildType) != type) continue;
comptime var child_name = decl.name;
if (@hasDecl(T, "_" ++ decl.name ++ "_Name"))
child_name = @field(T, "_" ++ decl.name ++ "_Name");
const child = try lookupAndRegister(world, parent, child_name, ChildType, error_writer);
try lookupAndRegisterDeclarations(world, child, ChildType, error_writer);
}
}
};
}