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