pi

README

pi

The retro game development engine for Go, inspired by Pico-8 and powered by Ebitengine.

FAQ

Is this a new fantasy console?

No, it's not. It's rather a game development library with dev-tools which make it simple (and fun!) to write retro games in Go.

What is a retro game?

It's a game that resembles old 8-bit/16-bit games. This usually means:

• (extremely) Low resolution (like 128x128 pixels)
• Limited number of colors (like 16)
• Very small number of assets (like 256 sprites, map having up to 8K tiles)
• Small number lines of code (thousands rather than millions)
• Sound effects and music made using predefined synth instruments and effects

What similarities does Pi have with Pico-8?

• Most API function names are similar and behave the same way.
• Screen resolution is small, and the number of colors is limited. Although in Pi you can change the resolution and palette.
• You have one small sprite sheet.

Why would I use it?

Because it's the easiest way to write a game in Go. IMHO ;)

Is Pi ready to use?

Pi is under development. Only limited functionality is provided. API is not stable. See ROADMAP for details.

How to get started?

1. Install dependencies
   • Go 1.18+
   • If not on Windows, please install additional dependencies for Linux or macOS.
2. Try examples from examples directory.
3. Create a new game using provided Github template.
4. Read the documentation.

Documentation

Overview

Package pi provides API to develop retro games.

Please note that the entire pi package is not concurrency-safe. This means that it is unsafe to run functions and access package variables from go-routines started by your code.

Index

• Constants
• Variables
• func Atan2(dx, dy float64) float64
• func Btn(button Button) bool
• func BtnBits() int
• func BtnPlayer(button Button, player int) bool
• func Btnp(button Button) bool
• func BtnpBits() int
• func BtnpPlayer(button Button, player int) bool
• func Camera(x, y int) (prevX, prevY int)
• func CameraReset() (prevX, prevY int)
• func Circ(centerX, centerY, radius int, color byte)
• func CircFill(centerX, centerY, radius int, color byte)
• func Clip(x, y, w, h int) (prevX, prevY, prevW, prevH int)
• func ClipReset() (prevX, prevY, prevW, prevH int)
• func Cls()
• func ClsCol(col byte)
• func Cos(angle float64) float64
• func Line(x0, y0, x1, y1 int, color byte)
• func Load(resources fs.ReadFileFS)
• func MouseBtn(b MouseButton) bool
• func MouseBtnp(b MouseButton) bool
• func MousePos() (x, y int)
• func Pal(color byte, replacementColor byte)
• func PalDisplay(color byte, replacementColor byte)
• func PalReset()
• func Palt(color byte, transparent bool)
• func PaltReset()
• func Pget(x, y int) byte
• func Print(text string, x, y int, color byte) (rightMostX int)
• func Pset(x, y int, color byte)
• func Rect(x0, y0, x1, y1 int, color byte)
• func RectFill(x0, y0, x1, y1 int, color byte)
• func Reset()
• func SetCustomFontHeight(height int)
• func SetCustomFontSpecialWidth(w int)
• func SetCustomFontWidth(w int)
• func SetScreenSize(w, h int)
• func Sget(x, y int) byte
• func Sin(angle float64) float64
• func Spr(n, x, y int)
• func SprSize(n, x, y int, w, h float64)
• func SprSizeFlip(n, x, y int, w, h float64, flipX, flipY bool)
• func Sset(x, y int, color byte)
• func Stop()
• func Time() float64
• func UseEmptySpriteSheet(w, h int)
• type Button
• type Controller
• type Font
  • func CustomFont() Font
  • func SystemFont() Font
  • func (f Font) Print(text string, x, y int, color byte) int
• type MouseButton
• type Position
• type Region
• type Screen
  • func Scr() Screen
• type SpriteSheet
  • func SprSheet() SpriteSheet

Constants

const (
	Left  = 0
	Right = 1
	Up    = 2
	Down  = 3
	O     = 4 // O is a first fire button
	X     = 5 // X is a second fire button
)

Keyboard mappings:

player 0: [DPAD] - cursors  [O] - Z C N   [X] - X V M
player 1: [DPAD] - SFED     [O] - LSHIFT  [X] - TAB W Q A

First connected gamepad controller is player 0, second player 1 and so on. On XBox controller O is A and Y, X is B and X.

const (
	MouseLeft   = 0
	MouseMiddle = 1
	MouseRight  = 2
)

const (
	SpriteWidth, SpriteHeight = 8, 8
)

Variables

var (
	// Update is a user provided function executed each frame (30 times per second).
	//
	// The purpose of this function is to handle user input, perform calculations, update
	// game state etc. Typically, this function does not draw on screen.
	Update func()

	// Draw is a user provided function executed at most each frame (up to 30 times per second).
	// π may skip calling this function if previous frame took too long.
	//
	// The purpose of this function is to draw on screen.
	Draw func()

	// Palette has all colors available in the game. Up to 256.
	// Palette is taken from loaded sprite sheet (which must be
	// a PNG file with indexed color mode). If sprite-sheet.png was not
	// found, then default 16 color palette is used.
	//
	// Can be freely read and updated. Changes will be visible immediately.
	Palette = defaultPalette
)

User parameters.

var (
	// DrawPalette contains mapping of colors used to replace color with
	// another one for all subsequent drawings.
	//
	// The index of array is original color, the value is color replacement.
	DrawPalette [256]byte

	// DisplayPalette contains mapping of colors used to replace color with
	// another one for the entire screen, at the end of a frame
	//
	// The index of array is original color, the value is color replacement.
	DisplayPalette [256]byte

	// ColorTransparency contains information whether given color is transparent.
	//
	// The index of array is a color number.
	ColorTransparency = defaultTransparency

	// TimeSeconds is the number of seconds since game was started
	TimeSeconds float64

	GameLoopStopped bool
)

var Controllers [8]Controller // 0th element is for Player 0, 1st for Player 1 etc.

Functions

func Atan2

func Atan2(dx, dy float64) float64

Atan2 converts DX, DY into an angle from 0..1

Similar to Cos and Sin, angle is taken to run anticlockwise in screenspace. For example:

atan(0,-1)  // returns 0.25

func Btn

func Btn(button Button) bool

Btn returns true if a controller button is being pressed at this moment by player 0.

func BtnBits

func BtnBits() int

BtnBits returns the state of all controller buttons for players 0 and 1 as bitset.

The first byte contains the button states for player 0 (bits 0 through 5, bits 6 and 7 are unused). The second byte contains the button states for player 1 (bits 8 through 13).

Bit 0 is Left, 1 is Right, bit 5 is the X button.

A bit of 1 means the button is pressed.

func BtnPlayer

func BtnPlayer(button Button, player int) bool

BtnPlayer returns true if a controller button is being pressed at this moment by specific player. The player can be 0..7.

func Btnp

func Btnp(button Button) bool

Btnp returns true when the controller button has just been pressed. It also returns true after the next 15 frames, and then every 4 frames. This simulates keyboard-like repeating.

func BtnpBits

func BtnpBits() int

BtnpBits returns the state of all controller buttons for players 0 and 1 as bitset.

The first byte contains the button states for player 0 (bits 0 through 5, bits 6 and 7 are unused). The second byte contains the button states for player 1 (bits 8 through 13).

Bit 0 is Left, 1 is Right, bit 5 is the X button.

A bit of 1 means the button has just been pressed.

func BtnpPlayer

func BtnpPlayer(button Button, player int) bool

BtnpPlayer returns true when the controller button has just been pressed. It also returns true after the next 15 frames, and then every 4 frames. This simulates keyboard-like repeating. The player can be 0..7.

func Camera

func Camera(x, y int) (prevX, prevY int)

Camera sets the camera offset used for all subsequent draw operations.

func CameraReset

func CameraReset() (prevX, prevY int)

CameraReset resets the camera offset to origin (0,0).

func Circ

func Circ(centerX, centerY, radius int, color byte)

Circ draws a circle

Circ takes into account camera position, clipping region and draw palette.

func CircFill

func CircFill(centerX, centerY, radius int, color byte)

CircFill draws a filled circle

CircFill takes into account camera position, clipping region and draw palette.

func Clip

func Clip(x, y, w, h int) (prevX, prevY, prevW, prevH int)

Clip sets the clipping region in the form of rectangle. All screen drawing operations will not affect any pixels outside the region.

Clip returns previous clipping region.

func ClipReset

func ClipReset() (prevX, prevY, prevW, prevH int)

ClipReset resets the clipping region, which means that entire screen will be clipped.

func Cls

func Cls()

Cls cleans the entire screen with color 0. It does not take into account any draw state parameters such as clipping region or camera.

func ClsCol

func ClsCol(col byte)

ClsCol cleans the entire screen with specified color. It does not take into account any draw state parameters such as clipping region or camera.

func Cos

func Cos(angle float64) float64

Cos returns the cosine of angle which is in the range of 0.0-1.0 measured clockwise.

If you want to use conventional radian-based function use math.Cos.

func Line

func Line(x0, y0, x1, y1 int, color byte)

Line draws a line between points x0,y0 and x1,y1 (inclusive).

Line takes into account camera position, clipping region and draw palette.

func Load

func Load(resources fs.ReadFileFS)

Load loads files like sprite-sheet.png, custom-font.png

func MouseBtn

func MouseBtn(b MouseButton) bool

MouseBtn returns true if the mouse button is being pressed at this moment.

func MouseBtnp

func MouseBtnp(b MouseButton) bool

MouseBtnp returns true when the mouse button has just been pressed. It also returns true after the next 15 frames, and then every 4 frames. This simulates keyboard-like repeating.

func MousePos

func MousePos() (x, y int)

MousePos returns the position of mouse in screen coordinates.

func Pal

func Pal(color byte, replacementColor byte)

Pal replaces color with another one for all subsequent drawings (it is changing the so-called draw palette).

Affected functions are Pset, Spr, SprSize, SprSizeFlip, Rect and RectFill.

func PalDisplay

func PalDisplay(color byte, replacementColor byte)

PalDisplay replaces color with another one for the whole screen at the end of a frame (it is changing the so-called display palette).

func PalReset

func PalReset()

PalReset resets all swapped colors for all palettes.

func Palt

func Palt(color byte, transparent bool)

Palt sets color transparency. If true then the color will not be drawn for next drawing operations.

Color transparency is used by Spr, SprSize and SprSizeFlip.

func PaltReset

func PaltReset()

PaltReset sets all transparent colors to false and makes color 0 transparent.

func Pget

func Pget(x, y int) byte

Pget gets a pixel color on the screen.

func Print

func Print(text string, x, y int, color byte) (rightMostX int)

Print prints text on the screen using system font. It takes into consideration clipping region and camera position.

Only unicode characters with code < 256 are supported. Unsupported chars are printed as question mark. The entire table of available chars can be found here: https://github.com/elgopher/pi/blob/master/internal/system-font.png

Print returns the right-most x position that occurred while printing.

func Pset

func Pset(x, y int, color byte)

Pset sets a pixel color on the screen.

func Rect

func Rect(x0, y0, x1, y1 int, color byte)

Rect draws a rectangle between points x0,y0 and x1,y1 (inclusive).

Rect takes into account camera position, clipping region and draw palette.

func RectFill

func RectFill(x0, y0, x1, y1 int, color byte)

RectFill draws a filled rectangle between points x0,y0 and x1,y1 (inclusive).

RectFill takes into account camera position, clipping region and draw palette.

func Reset

func Reset()

func SetCustomFontHeight

func SetCustomFontHeight(height int)

func SetCustomFontSpecialWidth

func SetCustomFontSpecialWidth(w int)

func SetCustomFontWidth

func SetCustomFontWidth(w int)

func SetScreenSize

func SetScreenSize(w, h int)

func Sget

func Sget(x, y int) byte

Sget gets the pixel color on the sprite sheet.

func Sin

func Sin(angle float64) float64

Sin returns the sine of angle which is in the range of 0.0-1.0 measured clockwise.

Sin returns an inverted result to suit screen space (where Y means "DOWN", as opposed to mathematical diagrams where Y typically means "UP"):

sin(0.25) // returns -1

If you want to use conventional radian-based function without the y inversion, use math.Sin.

func Spr

func Spr(n, x, y int)

Spr draws a sprite with specified number on the screen. Sprites are counted from left to right, top to bottom. Sprite 0 is on top-left corner, sprite 1 is to the right and so on.

func SprSize

func SprSize(n, x, y int, w, h float64)

SprSize draws a range of sprites on the screen.

n is a sprite number in the top-left corner.

Non-integer w or h may be used to draw partial sprites.

func SprSizeFlip

func SprSizeFlip(n, x, y int, w, h float64, flipX, flipY bool)

SprSizeFlip draws a range of sprites on the screen.

If flipX is true then sprite is flipped horizontally. If flipY is true then sprite is flipped vertically.

func Sset

func Sset(x, y int, color byte)

Sset sets the pixel color on the sprite sheet. It does not update the global Color.

func Stop

func Stop()

Stop will stop the game loop after Update or Draw is finished. If you are using devtools, the game will be paused. Otherwise, the game will be closed.

func Time

func Time() float64

Time returns the amount of time since game was run, as a (fractional) number of seconds.

Calling Time() multiple times in the same frame will always return the same result.

func UseEmptySpriteSheet

func UseEmptySpriteSheet(w, h int)

UseEmptySpriteSheet initializes empty sprite-sheet with given size. Could be used when you don't have sprite-sheet.png in resources.

Types

type Button

type Button int

Button is a virtual button on any game controller. The game controller can be a gamepad or a keyboard.

Button is used by Btn, Btnp, BtnPlayer, BtnpPlayer, BtnBits and BtnpBits.

type Controller

type Controller struct {
	// BtnDuration is how many frames button was pressed:
	// Index of array is equal to controller button constant.
	BtnDuration [6]uint
}

type Font

type Font struct {
	// Data contains all 256 characters sorted by their ascii-like number.
	// Each character is 8 subsequent bytes, starting from the top.
	// Left-most pixel in a line is bit 0. Right-most pixel in a line is bit 7.
	//
	// The size of slice is always 8 * 256 = 2048.
	//
	// Can be freely read and updated. Changes will be visible immediately.
	Data []byte
	// Width in pixels for all characters below 128. For Width > 8 only 8 pixels are drawn.
	Width int
	// SpecialWidth is a with of all special characters (code>=128)
	// For SpecialWidth > 8 only 8 pixels are drawn.
	SpecialWidth int
	// Height of line
	Height int
}

Font contains all information about loaded font and provides method to Print the text.

func CustomFont

func CustomFont() Font

func SystemFont

func SystemFont() Font

func (Font) Print

func (f Font) Print(text string, x, y int, color byte) int

Print prints text on the screen at given coordinates. It takes into account clipping region and camera position.

Only unicode characters with code < 256 are supported. Unsupported chars are printed as question mark. The entire table of available chars can be found here: https://github.com/elgopher/pi/blob/master/internal/system-font.png

Print returns the right-most x position that occurred while printing.

type MouseButton

type MouseButton int

type Position

type Position struct {
	X, Y int
}

var (
	// MouseBtnDuration has how many frames in a row a mouse button was pressed:
	// Index of array is equal to mouse button constant.
	MouseBtnDuration [3]uint

	// MousePosition is the position of mouse in screen coordinates.
	MousePosition Position
)

type Region

type Region struct {
	X, Y, W, H int
}

type Screen

type Screen struct {
	// Width and height in pixels
	W, H int

	// Pix contains pixel colors for the screen visible by the player.
	// Each pixel is one byte. It is initialized during pi.Boot.
	//
	// Pix on the screen are organized from left to right,
	// top to bottom. Slice element number 0 has pixel located
	// in the top-left corner. Slice element number 1 has pixel color
	// on the right and so on.
	//
	// Can be freely read and updated. Useful when you want to use your own
	// functions for pixel manipulation.
	Pix []byte

	Clip Region

	Camera Position
	// contains filtered or unexported fields
}

func Scr

func Scr() Screen

type SpriteSheet

type SpriteSheet struct {
	// Width and height in pixels
	W, H int

	// Pix contains pixel colors for the entire sprite sheet.
	// Each pixel is one byte. It is initialized during pi.Boot.
	//
	// Pixels in the sprite-sheet are organized from left to right,
	// top to bottom. Slice element number 0 has pixel located
	// in the top-left corner. Slice element number 1 has a pixel color
	// on the right and so on.
	//
	// Can be freely read and updated.
	// Useful when you want to use your own functions for pixel manipulation.
	Pix []byte
	// contains filtered or unexported fields
}

func SprSheet

func SprSheet() SpriteSheet