oak

README

Oak

A pure Go game engine

Installation

go get -u github.com/oakmound/oak/...

On linux, for audio, see klangsynthese for audio installation requirements

Usage

This is an example of the most basic oak program:

oak.AddScene("firstScene",
    // Initialization function
    func(prevScene string, inData interface{}) {}, 
    // Loop to continue or stop current scene
    func()bool{return true}, 
    // Exit to transition to next scene
    func()(nextScene string, result *oak.SceneResult){return "firstScene", nil}) 
oak.Init("firstScene")

See the examples folder for longer demos, godoc for reference documentation, and the wiki for more guided feature sets, tutorials and walkthroughs.

Motivation

The initial version of oak was made to support Oakmound Studio's game, Agent Blue, and was developed in parallel. Oak supports Windows with no dependencies and Linux with limited audio dependencies. We don't own a machine to check with, but hypothetically it supports OSX as well. We hope that users will be able to make great pure Go games with oak and welcome improvements.

Because Oak wants to have as few non-Go dependencies as possible, Oak does not use OpenGL or GLFW. We're open to adding support for these in the future for performance gains, but we always want an alternative that requires zero or near-zero dependencies. (We are very sad about the linux audio dependency and are considering writing an audio driver just to get rid of it.)

Support

For talk about the engine or help, that is not significant enough to be an Issue or PR, see the #oak channel on the gophers slack.

Features

1. Window Rendering
   • Windows and key events forked from shiny
   • Logical frame rate distinct from Draw rate
2. Image Management
   • render.Renderable interface
   • Sprite Sheet Batch Loading at startup
   • Manipulation
     • render.Modifiable interface
     • Built in Transformations and Filters
     • Some built-ins via gift
     • Extensible Modification syntax func(image.Image) *image.RGBA
   • Built in Renderable types
     • Sprite
     • Primitive builders, ColorBox, Line, Bezier
     • Sequence for animations
     • Switch for conditionally displaying one other Renderable
     • Composite for displaying multiple Renderables as one
     • History-tracking Reverting
   • Primarily 2D
3. Particle System
4. Mouse Handling
   • Click Collision
   • MouseEnter / MouseExit reaction events
   • Drag Handling
5. Audio Support
   • From klangsynthese
   • Batch Loading
   • Positional filters to pan and scale audio based on a listening position
6. Collision
   • Collision R-Tree forked from rtreego
   • 2D Raycasting
   • Collision Spaces
     • Attachable to Objects
     • Auto React to collisions through events
     • OnHit bindings func(s1,s2 *collision.Space)
     • Start/Stop collision with targeted objects
7. Physics System
   • Vectors
     • Attachable to Objects / Renderables
     • Momentum
     • Friction
     • Force / Pushing
8. Event Handler, Bus
   • PubSub system
   • event.CID can Bind(fn,eventName) and selectively Trigger(eventName) events
   • GlobalBind and event.Trigger for entity-independent
9. Timing utilities
   • Smoothed draw rate, frame rate tracking
   • FPS conversion to time.Duration
   • Manipulatable time.Ticker to readily change frame rate
10. Shaping
    • Shapes from func(x float64) (y float64) equations
    • Shapes from func(x,y,w,h int) bool containment
    • Convert shapes into:
      • Containment checks
      • Outlines
      • 2D arrays
11. Custom Console Commands
12. Logging
    • Swappable with custom implementations
    • Default Implementation: 4 log levels, writes to file and stdout

Documentation

Overview

Package oak is a game engine. It provides scene control, control over windows and what is drawn to them, propagates regular events to evaluate game logic, and so on.

Index

• Constants
• Variables
• func Add(name string, start scene.Start, loop scene.Loop, end scene.End) error
• func AddCommand(s string, fn func([]string)) error
• func AddScene(name string, s scene.Scene) error
• func BindKey(key string, binding string)
• func BindKeyBindings(r io.Reader) error
• func BindKeys(bindings KeyBindings)
• func ChangeWindow(width, height int)
• func ClearScreenFilter()
• func GetKeyBind(key string) string
• func GetScreen() *image.RGBA
• func Init(firstScene string)
• func IsDown(key string) (k bool)
• func IsHeld(key string) (k bool, d time.Duration)
• func LoadConf(filePath string) error
• func LoadConfData(r io.Reader) error
• func MoveWindow(x, y, w, h int) error
• func Quit()
• func ScreenShot() *image.RGBA
• func SeedRNG(inSeed int64)
• func SetAspectRatio(xToY float64)
• func SetBinaryPayload(payloadFn func(string) ([]byte, error), dirFn func(string) ([]string, error))
• func SetFullScreen(on bool) error
• func SetKeyBindings(r io.Reader) error
• func SetLang(s string)
• func SetLogicHandler(h event.Handler)
• func SetPalette(palette color.Palette)
• func SetScreen(x, y int)
• func SetScreenFilter(screenFilter mod.Filter)
• func SetViewportBounds(x1, y1, x2, y2 int)
• func ShakeScreen(dur time.Duration)
• func UnbindAllKeys()
• func UnbindKey(key string)
• func ViewVector() physics.Vector
• type Assets
• type Config
• type Debug
• type Driver
• type Font
• type FullScreenable
• type KeyBindings
  • func LoadKeyBindings(r io.Reader) (KeyBindings, error)
• type Language
• type MovableWindow
• type Screen
• type ScreenShaker
  • func (ss *ScreenShaker) Shake(dur time.Duration)

Constants

const (
	// DefaultSeed is a key int64 sent in to SeedRNG
	// used to indicate that the seed function should just
	// do the default operation for seeding, using the current
	// time.
	DefaultSeed int64 = iota
)

Variables

var (
	// Background is the uniform color drawn to the screen in between draw frames
	Background = image.Black
	// DrawTicker is the parallel to LogicTicker to set the draw framerate
	DrawTicker *timing.DynamicTicker
)

var (

	// ScreenWidth is the width of the screen
	ScreenWidth int
	// ScreenHeight is the height of the screen
	ScreenHeight int

	// FrameRate is the current logical frame rate.
	// Changing this won't directly effect frame rate, that
	// requires changing the LogicTicker, but it will take
	// effect next scene
	FrameRate int

	// DrawFrameRate is the equivalent to FrameRate for
	// the rate at which the screen is drawn.
	DrawFrameRate int
)

var (
	// ColorPalette is the current color palette oak is set to conform to. Modification of this
	// value directly will not effect oak's palette, use SetPalette instead. If SetPallete is never called,
	// this is the zero value ([]Color of length 0).
	ColorPalette color.Palette
)

var (
	// DefShaker is the global default shaker, used when oak.Shake is called.
	DefShaker = ScreenShaker{false, floatgeom.Point2{1.0, 1.0}}
)

var (
	DefaultDriver = driver.Main
)

Driver alternatives

var InitDriver = DefaultDriver

InitDriver is the driver oak will call during initialization

var (

	// LoadingR is a renderable that is displayed during loading screens.
	LoadingR render.Renderable
)

var (
	// SceneMap is a global map of scenes referred to when scenes advance to
	// determine what the next scene should be.
	// It can be replaced or modified so long as these modifications happen
	// during a scene or before oak has started.
	SceneMap = scene.NewMap()
)

var (
	// UseAspectRatio determines whether new window changes will distort or
	// maintain the relative width to height ratio of the screen buffer.
	UseAspectRatio = false
)

var (
	// ViewPos represents the point in the world which the viewport is anchored at.
	ViewPos = image.Point{}
)

Functions

func Add

func Add(name string, start scene.Start, loop scene.Loop, end scene.End) error

Add is shorthand for oak.SceneMap.Add

func AddCommand

func AddCommand(s string, fn func([]string)) error

AddCommand adds a console command to call fn when '<s> <args>' is input to the console. fn will be called with args split on whitespace.

func AddScene

func AddScene(name string, s scene.Scene) error

AddScene is shorthand for oak.SceneMap.AddScene

func BindKey

func BindKey(key string, binding string)

BindKey binds a name to be triggered when this key is triggered

func BindKeyBindings

func BindKeyBindings(r io.Reader) error

BindKeyBindings loads and binds KeyBindings at once. It maintains existing keybindings not a part of the input reader.

func BindKeys

func BindKeys(bindings KeyBindings)

BindKeys loops over and binds all pairs in the input KeyBindings

func ChangeWindow

func ChangeWindow(width, height int)

ChangeWindow sets the width and height of the game window. Although exported, calling it without a size event will probably not act as expected.

func ClearScreenFilter

func ClearScreenFilter()

ClearScreenFilter resets the draw function to no longer filter the screen before publishing it to the window.

func GetKeyBind

func GetKeyBind(key string) string

GetKeyBind returns either whatever name has been bound to a key or the key if nothing has been bound to it. Todo: this should be a var function that starts out as "return key", and only becomes this function when a binding is made.

func GetScreen

func GetScreen() *image.RGBA

GetScreen returns the current screen as an rgba buffer

func Init

func Init(firstScene string)

Init initializes the oak engine. It spawns off an event loop of several goroutines and loops through scenes after initialization.

func IsDown

func IsDown(key string) (k bool)

IsDown returns whether a key is held down

func IsHeld

func IsHeld(key string) (k bool, d time.Duration)

IsHeld returns whether a key is held down, and for how long

func LoadConf

func LoadConf(filePath string) error

LoadConf loads a config file, that could exist inside oak's binary data storage (see fileutil), to SetupConfig

func LoadConfData

func LoadConfData(r io.Reader) error

LoadConfData takes in an io.Reader and decodes it to SetupConfig

func MoveWindow

func MoveWindow(x, y, w, h int) error

MoveWindow sets the position of a window to be x,y and it's dimensions to w,h If the window does not support being positioned, it will report as such.

func Quit

func Quit()

Quit sends a signal to the window to close itself, ending oak.

func ScreenShot

func ScreenShot() *image.RGBA

ScreenShot takes a snap shot of the window's image content. ScreenShot is not safe to call while an existing ScreenShot call has yet to finish executing. This could change in the future.

func SeedRNG

func SeedRNG(inSeed int64)

SeedRNG seeds go's random number generator and logs the seed set to file.

func SetAspectRatio

func SetAspectRatio(xToY float64)

SetAspectRatio will enforce that the displayed window does not distort the input screen away from the given x:y ratio. The screen will not use these settings until a new size event is received from the OS.

func SetBinaryPayload

func SetBinaryPayload(payloadFn func(string) ([]byte, error), dirFn func(string) ([]string, error))

SetBinaryPayload just sets some public fields on packages that require access to binary functions as alternatives to os file functions. This is no longer necessary, as a single package uses these now.

func SetFullScreen

func SetFullScreen(on bool) error

SetFullScreen attempts to set the local oak window to be full screen. If the window does not support this functionality, it will report as such.

func SetKeyBindings

func SetKeyBindings(r io.Reader) error

SetKeyBindings removes all existing keybindings and then binds all bindings within the input reader.

func SetLang

func SetLang(s string)

SetLang parses a string as a language

func SetLogicHandler

func SetLogicHandler(h event.Handler)

SetLogicHandler swaps the logic system of the engine with some other implementation. If this is never called, it will use event.DefaultBus

func SetPalette

func SetPalette(palette color.Palette)

SetPalette tells oak to conform the screen to the input color palette before drawing.

func SetScreen

func SetScreen(x, y int)

SetScreen sends a signal to the draw loop to set the viewport to be at x,y

func SetScreenFilter

func SetScreenFilter(screenFilter mod.Filter)

SetScreenFilter will filter the screen by the given modification function prior to publishing the screen's rgba to be displayed.

func SetViewportBounds

func SetViewportBounds(x1, y1, x2, y2 int)

SetViewportBounds sets the minimum and maximum position of the viewport, including screen dimensions

func ShakeScreen

func ShakeScreen(dur time.Duration)

ShakeScreen will Shake using the package global DefShaker

func UnbindAllKeys

func UnbindAllKeys()

UnbindAllKeys clears the contents of the oak's keybindings.

func UnbindKey

func UnbindKey(key string)

UnbindKey removes the binding for the given key in oak's keybindings. Does nothing if the key is not already bound.

func ViewVector

func ViewVector() physics.Vector

ViewVector returns ViewPos as a Vector

Types

type Assets

type Assets struct {
	AssetPath string `json:"assetPath"`
	AudioPath string `json:"audioPath"`
	ImagePath string `json:"imagePath"`
	FontPath  string `json:"fontPath"`
}

Assets is a json type storing paths to different asset folders

type Config

type Config struct {
	Assets              Assets `json:"assets"`
	Debug               Debug  `json:"debug"`
	Screen              Screen `json:"screen"`
	Font                Font   `json:"font"`
	FrameRate           int    `json:"frameRate"`
	DrawFrameRate       int    `json:"drawFrameRate"`
	Language            string `json:"language"`
	Title               string `json:"title"`
	BatchLoad           bool   `json:"batchLoad"`
	GestureSupport      bool   `json:"gestureSupport"`
	LoadBuiltinCommands bool   `json:"loadBuiltinCommands"`
}

Config stores initialization settings for oak.

var (
	// SetupConfig is the config struct read from at initialization time
	// when oak starts. When oak.Init() is called, the variables behind
	// SetupConfig are passed to their appropriate places in the engine, and
	// afterword the variable is unused.
	SetupConfig Config
)

type Debug

type Debug struct {
	Filter string `json:"filter"`
	Level  string `json:"level"`
}

Debug is a json type storing the starting debug filter and level

type Driver

type Driver func(f func(screen.Screen))

A Driver is a function which can take in our lifecycle function and initialize oak with the OS interfaces it needs.

type Font

type Font struct {
	Hinting string  `json:"hinting"`
	Size    float64 `json:"size"`
	DPI     float64 `json:"dpi"`
	File    string  `json:"file"`
	Color   string  `json:"color"`
}

Font is a json type storing the default font settings

type FullScreenable

type FullScreenable interface {
	SetFullScreen(bool) error
}

FullScreenable defines windows that can be set to full screen.

type KeyBindings

type KeyBindings map[string]string

KeyBindings map input keys to meaningful names, so code can be built around those meaningufl names and users can easily rebind which keys do what.

func LoadKeyBindings

func LoadKeyBindings(r io.Reader) (KeyBindings, error)

LoadKeyBindings converts a reader into a map of keys to meaningful names. It expects a simple .toml syntax, of key = "value" pairs per line. The resulting KeyBindings will have the keys and values reversed, so `MoveUp = "W"` will correspond to kb["W"] = "MoveUp"

type Language

type Language int

Language is hypothetically something games might care about in their text work: Consider moving this to oakerr, and also moving all strings to oakerr so messages output by the engine are localized.

const (
	ENGLISH Language = iota
	GERMAN
)

Lang enumerator

var (
	// Lang is the current langugae
	Lang Language
)

type MovableWindow

type MovableWindow interface {
	MoveWindow(x, y, w, h int32) error
}

MovableWindow defines windows that can have their position set

type Screen

type Screen struct {
	X      int `json:"X"`
	Y      int `json:"Y"`
	Height int `json:"height"`
	Width  int `json:"width"`
	Scale  int `json:"scale"`
}

Screen is a json type storing the starting screen width and height

type ScreenShaker

type ScreenShaker struct {
	Random    bool
	Magnitude floatgeom.Point2
}

A ScreenShaker knows how to shake a screen by a (or up to a) given magnitude. If Random is true, the Shaker will shake up to the (negative or positive) magnitude of each the X and Y axes. Otherwise, it will oscillate between negative magnitude and positive magnitude.

func (*ScreenShaker) Shake

func (ss *ScreenShaker) Shake(dur time.Duration)

Shake shakes the screen based on this shaker's attributes. See ScreenShaker.