resources/images: Add $image.Colors

Which returns the most dominant colors of an image using a simple histogram method.

Fixes #10307

resources/images/color.go

@@ -45,6 +45,14 @@ func ReplaceColorInPalette(c color.Color, p color.Palette) {
 	p[p.Index(c)] = c
 }
 
+// ColorToHexString converts a color to a hex string.
+func ColorToHexString(c color.Color) string {
+	r, g, b, a := c.RGBA()
+	rgba := color.RGBA{uint8(r), uint8(g), uint8(b), uint8(a)}
+	return fmt.Sprintf("#%.2x%.2x%.2x", rgba.R, rgba.G, rgba.B)
+
+}
+
 func hexStringToColor(s string) (color.Color, error) {
 	s = strings.TrimPrefix(s, "#")
 

resources/images/color_test.go

@@ -60,6 +60,30 @@ func TestHexStringToColor(t *testing.T) {
 	}
 }
 
+func TestColorToHexString(t *testing.T) {
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		arg    color.Color
+		expect string
+	}{
+		{color.White, "#ffffff"},
+		{color.Black, "#000000"},
+		{color.RGBA{R: 0x42, G: 0x87, B: 0xf5, A: 0xff}, "#4287f5"},
+	} {
+
+		test := test
+		c.Run(test.expect, func(c *qt.C) {
+			c.Parallel()
+
+			result := ColorToHexString(test.arg)
+
+			c.Assert(result, qt.Equals, test.expect)
+		})
+
+	}
+}
+
 func TestAddColorToPalette(t *testing.T) {
 	c := qt.New(t)
 

resources/images/image_resource.go

@@ -48,6 +48,10 @@ type ImageResourceOps interface {
 	// Exif returns an ExifInfo object containing Image metadata.
 	Exif() *exif.ExifInfo
 
+	// Colors returns a slice of the most dominant colors in an image
+	// using a simple histogram method.
+	Colors() ([]string, error)
+
 	// Internal
 	DecodeImage() (image.Image, error)
 }