go-chart/drawing/color.go
2016-07-09 11:23:35 -07:00

86 lines
1.8 KiB
Go

package drawing
import (
"fmt"
"strconv"
)
var (
// ColorTransparent is a fully transparent color.
ColorTransparent = Color{}
// ColorWhite is white.
ColorWhite = Color{R: 255, G: 255, B: 255, A: 255}
// ColorBlack is black.
ColorBlack = Color{R: 0, G: 0, B: 0, A: 255}
// ColorRed is red.
ColorRed = Color{R: 255, G: 0, B: 0, A: 255}
// ColorGreen is green.
ColorGreen = Color{R: 0, G: 255, B: 0, A: 255}
// ColorBlue is blue.
ColorBlue = Color{R: 0, G: 0, B: 255, A: 255}
)
func parseHex(hex string) uint8 {
v, _ := strconv.ParseInt(hex, 16, 16)
return uint8(v)
}
// ColorFromHex returns a color from a css hex code.
func ColorFromHex(hex string) Color {
var c Color
if len(hex) == 3 {
c.R = parseHex(string(hex[0])) * 0x11
c.G = parseHex(string(hex[1])) * 0x11
c.B = parseHex(string(hex[2])) * 0x11
} else {
c.R = parseHex(string(hex[0:2]))
c.G = parseHex(string(hex[2:4]))
c.B = parseHex(string(hex[4:6]))
}
c.A = 255
return c
}
// Color is our internal color type because color.Color is bullshit.
type Color struct {
R uint8
G uint8
B uint8
A uint8
}
// RGBA returns the color as a pre-alpha mixed color set.
func (c Color) RGBA() (r, g, b, a uint32) {
fa := float64(c.A) / 255.0
r = uint32(float64(uint32(c.R)) * fa)
r |= r << 8
g = uint32(float64(uint32(c.G)) * fa)
g |= g << 8
b = uint32(float64(uint32(c.B)) * fa)
b |= b << 8
a = uint32(c.A)
a |= a << 8
return
}
// IsZero returns if the color has been set or not.
func (c Color) IsZero() bool {
return c.R == 0 && c.G == 0 && c.B == 0 && c.A == 0
}
// IsTransparent returns if the colors alpha channel is zero.
func (c Color) IsTransparent() bool {
return c.A == 0
}
// String returns a css string representation of the color.
func (c Color) String() string {
fa := float64(c.A) / float64(255)
return fmt.Sprintf("rgba(%v,%v,%v,%.1f)", c.R, c.G, c.B, fa)
}