hello.go

// +build examples

// MIT License
//
// Copyright (c) 2021 Wojciech Franczyk
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package main

import (
	"github.com/wfranczyk/ento"
)

type Component1 struct{ value int }
type Component2 struct{ value int }
type Component3 struct{ value int }

type System struct {
	// Always use pointer to base component type (!)
	// Add `ento` tag to automatically bind components
	C1 *Component1 `ento:"required"`
	C2 *Component2 `ento:"required"`
	C3 *Component2 `ento:"optional"`

	// Systems can have non-component-bound fields
	calls int
}

// Update implements ento.System
// Based on `ento` tag, entities will be selected for update by the system.
// Entities that do not contain all the `required` components will be skipped.
func (s *System) Update(entity *ento.Entity) {
	// Before Update is called, all tagged components
	// will be replaced with values from entity
	s.C1.value += s.C2.value

	// Optional field will be set to null if entity does not contain them
	if s.C3 != nil {
		s.C1.value += s.C3.value
	}

	s.calls++
}

func main() {
	// Create the world and register components
	world := ento.NewWorldBuilder().
		// Use "zero-values" as values are ignored when registering
		WithSparseComponents(Component1{}, Component2{}, Component3{}).
		// Pre-allocate space for 256 entities (world can grow beyond that automatically)
		Build(256)

	// Add systems
	system := &System{}
	world.AddSystems(system)

	// Create an entity (it is added to the world immediately)
	entity := world.AddEntity(Component1{1}, Component2{1})

	// Use Set to add or change entity components
	entity.Set(Component3{1})

	// Update the world
	world.Update()
	println(system.calls) // prints: 1

	// Use Get to receive component value (or nil if not present)
	var c1 *Component1
	entity.Get(&c1)
	println(c1.value == 3) // prints: true

	// Use Rem to remove component from entity
	// As Component2 is `required` in the System
	// it will no longer be updated by it
	entity.Rem(Component2{})

	world.Update()
	println(system.calls) // prints: 1 - the system was not called

	entity.Get(&c1)
	println(c1.value == 3) // true - the entity is no longer updated by the system
}