Add Luminance to Color

To sort an image's colors from darkest to lightest, you can then do:

```handlebars
{{ {{ $colorsByLuminance := sort $image.Colors "Luminance" }}
```

This uses the formula defined here: https://www.w3.org/TR/WCAG21/#dfn-relative-luminance

Fixes #10450

1 files changed, 14 insertions, 10 deletions

diff --git a/resources/images/filters.go b/resources/images/filters.go
index 53818c97d..0a620716d 100644
--- a/resources/images/filters.go
+++ b/resources/images/filters.go
@@ -1,4 +1,4 @@
-// Copyright 2019 The Hugo Authors. All rights reserved.
+// Copyright 2024 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -65,7 +65,7 @@ func (*Filters) Opacity(opacity any) gift.Filter {
 func (*Filters) Text(text string, options ...any) gift.Filter {
 	tf := textFilter{
 		text:        text,
-		color:       "#ffffff",
+		color:       color.White,
 		size:        20,
 		x:           10,
 		y:           10,
@@ -78,7 +78,9 @@ func (*Filters) Text(text string, options ...any) gift.Filter {
 		for option, v := range opt {
 			switch option {
 			case "color":
-				tf.color = cast.ToString(v)
+				if color, ok, _ := toColorGo(v); ok {
+					tf.color = color
+				}
 			case "size":
 				tf.size = cast.ToFloat64(v)
 			case "x":
@@ -128,15 +130,14 @@ func (*Filters) Padding(args ...any) gift.Filter {
 
 	var top, right, bottom, left int
 	var ccolor color.Color = color.White // canvas color
-	var err error
 
 	_args := args // preserve original args for most stable hash
 
-	if vcs, ok := (args[len(args)-1]).(string); ok {
-		ccolor, err = hexStringToColor(vcs)
+	if vcs, ok, err := toColorGo(args[len(args)-1]); ok || err != nil {
 		if err != nil {
 			panic("invalid canvas color: specify RGB or RGBA using hex notation")
 		}
+		ccolor = vcs
 		args = args[:len(args)-1]
 		if len(args) == 0 {
 			panic("not enough arguments: provide one or more padding values using the CSS shorthand property syntax")
@@ -180,12 +181,11 @@ func (*Filters) Padding(args ...any) gift.Filter {
 // Dither creates a filter that dithers an image.
 func (*Filters) Dither(options ...any) gift.Filter {
 	ditherOptions := struct {
-		Colors     []string
+		Colors     []any
 		Method     string
 		Serpentine bool
 		Strength   float32
 	}{
-		Colors:     []string{"000000ff", "ffffffff"},
 		Method:     "floydsteinberg",
 		Serpentine: true,
 		Strength:   1.0,
@@ -198,14 +198,18 @@ func (*Filters) Dither(options ...any) gift.Filter {
 		}
 	}
 
+	if len(ditherOptions.Colors) == 0 {
+		ditherOptions.Colors = []any{"000000ff", "ffffffff"}
+	}
+
 	if len(ditherOptions.Colors) < 2 {
 		panic("palette must have at least two colors")
 	}
 
 	var palette []color.Color
 	for _, c := range ditherOptions.Colors {
-		cc, err := hexStringToColor(c)
-		if err != nil {
+		cc, ok, err := toColorGo(c)
+		if !ok || err != nil {
 			panic(fmt.Sprintf("%q is an invalid color: specify RGB or RGBA using hexadecimal notation", c))
 		}
 		palette = append(palette, cc)