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const std = @import("std");
const component = @import("component.zig");
const ComponentType = component.ComponentType;
pub const EntityComponentSystem = struct {
allocator: std.mem.Allocator,
components: std.MultiArrayList(component.Components),
available_ids: std.ArrayList(usize),
next_id: usize,
fn nullEntity(self: *EntityComponentSystem, entity: usize) void {
inline for (std.enums.valuesFromFields(ComponentType, std.meta.fields(ComponentType))) |comp| {
self.componentRemoveEntity(comp, entity);
}
}
pub fn init(allocator: std.mem.Allocator) EntityComponentSystem {
return EntityComponentSystem{
.allocator = allocator,
.components = .{},
.available_ids = std.ArrayList(usize).init(allocator),
.next_id = 0,
};
}
pub fn deinit(self: *EntityComponentSystem) void {
self.available_ids.deinit();
self.components.deinit(self.allocator);
}
pub fn createEntity(self: *EntityComponentSystem) !usize {
const id = self.available_ids.popOrNull() orelse noroom: {
const id = self.next_id;
try self.components.append(self.allocator, undefined);
self.next_id += 1;
break :noroom id;
};
self.nullEntity(id);
return id;
}
pub fn componentAddEntity(
self: *EntityComponentSystem,
comp: component.ComponentType,
entity: usize,
args: anytype,
) !void {
switch (comp) {
ComponentType.component_stub => self.components.items(.component_stub)[entity] = component.ComponentStub.init(args),
}
}
pub fn deleteEntity(self: *EntityComponentSystem, entity: usize) !void {
self.nullEntity(entity);
try self.available_ids.append(entity);
}
fn componentRemoveEntityGeneric(comp: anytype, entity: usize) void {
var fixed_comp = comp[entity] orelse return;
fixed_comp.deinit();
comp[entity] = null;
}
pub fn componentRemoveEntity(
self: *EntityComponentSystem,
comp: component.ComponentType,
entity: usize,
) void {
var components = self.components;
switch (comp) {
ComponentType.component_stub => componentRemoveEntityGeneric(components.items(.component_stub), entity),
}
}
};
test "add entities to components" {
var ecs = EntityComponentSystem.init(std.testing.allocator);
defer ecs.deinit();
for (0..100) |i| {
const entity = try ecs.createEntity();
try std.testing.expectEqual(i, entity);
try ecs.componentAddEntity(ComponentType.component_stub, entity, .{});
try std.testing.expect(ecs.components.items(.component_stub)[entity] != null);
}
}
test "remove entities from components" {
var ecs = EntityComponentSystem.init(std.testing.allocator);
defer ecs.deinit();
const entity = try ecs.createEntity();
try ecs.componentAddEntity(ComponentType.component_stub, entity, .{});
const entity2 = try ecs.createEntity();
try ecs.componentAddEntity(ComponentType.component_stub, entity2, .{});
try std.testing.expect(ecs.components.items(.component_stub)[entity2] != null);
ecs.componentRemoveEntity(ComponentType.component_stub, entity2);
try std.testing.expect(ecs.components.items(.component_stub)[entity2] == null);
}
test "delete entities" {
var ecs = EntityComponentSystem.init(std.testing.allocator);
defer ecs.deinit();
const entity = try ecs.createEntity();
try ecs.componentAddEntity(ComponentType.component_stub, entity, .{});
const entity2 = try ecs.createEntity();
try ecs.componentAddEntity(ComponentType.component_stub, entity2, .{});
try std.testing.expect(ecs.components.items(.component_stub)[entity2] != null);
try ecs.deleteEntity(entity2);
try std.testing.expect(ecs.components.items(.component_stub)[entity2] == null);
try std.testing.expectEqual(1, ecs.available_ids.items.len);
}
test "recycle entities" {
var ecs = EntityComponentSystem.init(std.testing.allocator);
defer ecs.deinit();
const entity = try ecs.createEntity();
try ecs.componentAddEntity(ComponentType.component_stub, entity, .{});
const entity2 = try ecs.createEntity();
try ecs.componentAddEntity(ComponentType.component_stub, entity2, .{});
try ecs.deleteEntity(entity2);
try std.testing.expectEqual(1, ecs.available_ids.items.len);
const entity3 = try ecs.createEntity();
try std.testing.expectEqual(1, entity3);
try std.testing.expectEqual(0, ecs.available_ids.items.len);
const entity4 = try ecs.createEntity();
try std.testing.expectEqual(2, entity4);
try ecs.deleteEntity(entity);
try std.testing.expectEqual(1, ecs.available_ids.items.len);
const entity5 = try ecs.createEntity();
try std.testing.expectEqual(0, entity5);
try std.testing.expectEqual(0, ecs.available_ids.items.len);
try ecs.deleteEntity(entity5);
try ecs.deleteEntity(entity4);
try ecs.deleteEntity(entity3);
try std.testing.expectEqual(3, ecs.available_ids.items.len);
}
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