refactor: change project structure and package name

pkg/drawing/color.go

@@ -0,0 +1,126 @@
+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
+}
+
+// ColorChannelFromFloat returns a normalized byte from a given float value.
+func ColorChannelFromFloat(v float64) uint8 {
+	return uint8(v * 255)
+}
+
+// Color is our internal color type because color.Color is bullshit.
+type Color struct {
+	R, G, B, 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
+}
+
+// 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,
+	}
+}
+
+// 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)
+}