zntg - a UI framework for Go
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package zntg
import (
"errors"
"image/color"
"regexp"
)
var hexColorRE = regexp.MustCompile(`^#?([0-9A-Fa-f]{2})-?([0-9A-Fa-f]{2})-?([0-9A-Fa-f]{2})-?([0-9A-Fa-f]{2})?$`)
// HexColor parses hexadecimal string s and returns the RGBA color. Accepted are 3 or 4 components (R, G, B, A) following an optional hash character '#'.
func HexColor(s string) (color.RGBA, error) {
match := hexColorRE.FindStringSubmatch(s)
if match == nil {
return color.RGBA{}, errors.New("invalid color format")
}
values, err := HexToInts(match[1:]...)
if err != nil {
return color.RGBA{}, err
}
a := 255
if len(match[4]) > 0 {
a = values[3]
}
return RGBA(uint8(values[0]), uint8(values[1]), uint8(values[2]), uint8(a)), nil
}
// HexToInt tries to convert a string with hexadecimal characters to an integer.
func HexToInt(s string) (int, error) {
var i int
for _, c := range s {
i *= 16
if c >= '0' && c <= '9' {
i += int(c - '0')
} else if c >= 'A' && c <= 'F' {
i += int(c - 'A' + 10)
} else if c >= 'a' && c <= 'f' {
i += int(c - 'a' + 10)
} else {
return 0, errors.New("hex digit not supported")
}
}
return i, nil
}
// HexToInts tries to convert multiple strings with hexadecimal characters to a slice of integers.
func HexToInts(s ...string) ([]int, error) {
ints := make([]int, len(s))
for i, s := range s {
value, err := HexToInt(s)
if err != nil {
return nil, err
}
ints[i] = value
}
return ints, nil
}
// MustHexColor parses hexadecimal string s and returns the RGBA color. If the conversion fails it panics.
func MustHexColor(s string) color.RGBA {
color, err := HexColor(s)
if err != nil {
panic(err)
}
return color
}
// RGB creates an opaque color with the specified red, green and red values.
func RGB(r, g, b byte) color.RGBA { return RGBA(r, g, b, 0xff) }
// RGB creates a color with the specified red, green, red and alpha values.
func RGBA(r, g, b, a byte) color.RGBA {
return color.RGBA{R: r, G: g, B: b, A: a}
}