A rendering engine library for Go supporting both SDL2 and WebAssembly (HTML Canvas) targets.
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package render
import (
"encoding/json"
"errors"
"fmt"
"image/color"
"regexp"
"strconv"
"github.com/vmihailenco/msgpack"
)
var (
// Regexps to parse hex color codes. Three formats are supported:
// * reHexColor3 uses only 3 hex characters, like #F90
// * reHexColor6 uses standard 6 characters, like #FF9900
// * reHexColor8 is the standard 6 plus alpha channel, like #FF9900FF
reHexColor3 = regexp.MustCompile(`^([A-Fa-f0-9])([A-Fa-f0-9])([A-Fa-f0-9])$`)
reHexColor6 = regexp.MustCompile(`^([A-Fa-f0-9]{2})([A-Fa-f0-9]{2})([A-Fa-f0-9]{2})$`)
reHexColor8 = regexp.MustCompile(`^([A-Fa-f0-9]{2})([A-Fa-f0-9]{2})([A-Fa-f0-9]{2})([A-Fa-f0-9]{2})$`)
)
// Color holds an RGBA color value.
type Color struct {
Red uint8
Green uint8
Blue uint8
Alpha uint8
}
// RGBA creates a new Color.
func RGBA(r, g, b, a uint8) Color {
return Color{
Red: r,
Green: g,
Blue: b,
Alpha: a,
}
}
// FromColor creates a render.Color from a Go color.Color
func FromColor(from color.Color) Color {
// downscale a 16-bit color value to 8-bit. input range 0x0000..0xffff
downscale := func(in uint32) uint8 {
var scale = float64(in) / 0xffff
return uint8(scale * 0xff)
}
r, g, b, a := from.RGBA()
return RGBA(
downscale(r),
downscale(g),
downscale(b),
downscale(a),
)
}
// MustHexColor parses a color from hex code or panics.
func MustHexColor(hex string) Color {
color, err := HexColor(hex)
if err != nil {
panic(err)
}
return color
}
// HexColor parses a color from hexadecimal code.
func HexColor(hex string) (Color, error) {
c := Black // default color
if len(hex) > 0 && hex[0] == '#' {
hex = hex[1:]
}
var m []string
if len(hex) == 3 {
m = reHexColor3.FindStringSubmatch(hex)
} else if len(hex) == 6 {
m = reHexColor6.FindStringSubmatch(hex)
} else if len(hex) == 8 {
m = reHexColor8.FindStringSubmatch(hex)
} else {
return c, errors.New("not a valid length for color code; only 3, 6 and 8 supported")
}
// Any luck?
if m == nil {
return c, errors.New("not a valid hex color code")
}
// Parse the color values. 16=base, 8=bit size
red, _ := strconv.ParseUint(m[1], 16, 8)
green, _ := strconv.ParseUint(m[2], 16, 8)
blue, _ := strconv.ParseUint(m[3], 16, 8)
// Alpha channel available?
var alpha uint64 = 255
if len(m) == 5 {
alpha, _ = strconv.ParseUint(m[4], 16, 8)
}
c.Red = uint8(red)
c.Green = uint8(green)
c.Blue = uint8(blue)
c.Alpha = uint8(alpha)
return c, nil
}
func (c Color) String() string {
return fmt.Sprintf(
"Color<#%02x%02x%02x+%02x>",
c.Red, c.Green, c.Blue, c.Alpha,
)
}
// ToHex converts a render.Color to standard #RRGGBB hexadecimal format.
func (c Color) ToHex() string {
return fmt.Sprintf(
"#%02x%02x%02x",
c.Red, c.Green, c.Blue,
)
}
// ToColor converts a render.Color into a Go standard color.Color
func (c Color) ToColor() color.RGBA {
return color.RGBA{
R: c.Red,
G: c.Green,
B: c.Blue,
A: c.Alpha,
}
}
// Transparent returns whether the alpha channel is zeroed out and the pixel
// won't appear as anything when rendered.
func (c Color) Transparent() bool {
return c.Alpha == 0x00
}
// MarshalJSON serializes the Color for JSON.
func (c Color) MarshalJSON() ([]byte, error) {
return []byte(fmt.Sprintf(
`"#%02x%02x%02x"`,
c.Red, c.Green, c.Blue,
)), nil
}
// UnmarshalJSON reloads the Color from JSON.
func (c *Color) UnmarshalJSON(b []byte) error {
var hex string
err := json.Unmarshal(b, &hex)
if err != nil {
return err
}
parsed, err := HexColor(hex)
if err != nil {
return err
}
c.Red = parsed.Red
c.Blue = parsed.Blue
c.Green = parsed.Green
c.Alpha = parsed.Alpha
return nil
}
func (c Color) EncodeMsgpack(enc *msgpack.Encoder) error {
return enc.EncodeString(fmt.Sprintf(
`"#%02x%02x%02x"`,
c.Red, c.Green, c.Blue,
))
}
func (c Color) DecodeMsgpack(dec *msgpack.Decoder) error {
hex, err := dec.DecodeString()
if err != nil {
return fmt.Errorf("Color.DecodeMsgpack: %s", err)
}
parsed, err := HexColor(hex)
if err != nil {
return fmt.Errorf("Color.DecodeMsgpack: HexColor: %s", err)
}
c.Red = parsed.Red
c.Blue = parsed.Blue
c.Green = parsed.Green
c.Alpha = parsed.Alpha
return nil
}
// // MarshalMsgpack serializes the Color for msgpack.
// func (c Color) MarshalMsgpack() ([]byte, error) {
// data := []uint8{
// c.Red, c.Green, c.Blue, c.Alpha,
// }
// return msgpack.Marshal(data)
// }
//
// // UnmarshalMsgpack decodes a Color from msgpack format.
// func (c *Color) UnmarshalMsgpack(b []byte) error {
// var data []uint8
// if err := msgpack.Unmarshal(data, b); err != nil {
// return err
// }
// c.Red = 255
// c.Green = data[1]
// c.Blue = data[2]
// c.Alpha = data[3]
// return nil
// }
// Add a relative color value to the color.
func (c Color) Add(r, g, b, a int) Color {
var (
R = int(c.Red) + r
G = int(c.Green) + g
B = int(c.Blue) + b
A = int(c.Alpha) + a
)
cap8 := func(v int) uint8 {
if v > 255 {
v = 255
} else if v < 0 {
v = 0
}
return uint8(v)
}
return Color{
Red: cap8(R),
Green: cap8(G),
Blue: cap8(B),
Alpha: cap8(A),
}
}
// Lighten a color value.
func (c Color) Lighten(v int) Color {
return c.Add(v, v, v, 0)
}
// Darken a color value.
func (c Color) Darken(v int) Color {
return c.Add(-v, -v, -v, 0)
}
// Transparentize adjusts the alpha value.
func (c Color) Transparentize(v int) Color {
return c.Add(0, 0, 0, v)
}
// SetAlpha sets the alpha value to a specific setting.
func (c Color) SetAlpha(v uint8) Color {
c.Alpha = v
return c
}