package render import ( "encoding/json" "errors" "fmt" "image/color" "regexp" "strconv" ) 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), ) } // ToRGBA converts to a standard Go color.Color func (c Color) ToRGBA() color.RGBA { return color.RGBA{ R: c.Red, G: c.Green, B: c.Blue, A: c.Alpha, } } // 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 } // IsZero returns if the color is all zeroes (invisible). func (c Color) IsZero() bool { return c.Red+c.Green+c.Blue+c.Alpha == 0 } // 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), } } // AddColor adds another Color to your Color. func (c Color) AddColor(other Color) Color { return c.Add( int(other.Red), int(other.Green), int(other.Blue), int(other.Alpha), ) } // 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 }