go-chart/drawing/color.go

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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
}
// ColorFromAlphaMixedRGBA returns the system alpha mixed rgba values.
func ColorFromAlphaMixedRGBA(r, g, b, a uint32) Color {
fa := float64(a) / 255.0
var c Color
c.R = uint8(float64(r) / fa)
c.G = uint8(float64(g) / fa)
c.B = uint8(float64(b) / fa)
c.A = uint8(a | (a >> 8))
return c
}
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// ColorChannelFromFloat returns a normalized byte from a given float value.
func ColorChannelFromFloat(v float64) uint8 {
return uint8(v * 255)
}
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// Color is our internal color type because color.Color is bullshit.
type Color struct {
R, G, B, A uint8
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}
// 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
}
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// WithAlpha returns a copy of the color with a given alpha.
func (c Color) WithAlpha(a uint8) Color {
return Color{
R: c.R,
G: c.G,
B: c.B,
A: a,
}
}
// Equals returns true if the color equals another.
func (c Color) Equals(other Color) bool {
return c.R == other.R &&
c.G == other.G &&
c.B == other.B &&
c.A == other.A
}
// AverageWith averages two colors.
func (c Color) AverageWith(other Color) Color {
return Color{
R: (c.R + other.R) >> 1,
G: (c.G + other.G) >> 1,
B: (c.B + other.B) >> 1,
A: c.A,
}
}
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// 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)
}