hugo/resources/images/color.go

// Copyright 2019 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.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package images

import (
	"encoding/hex"
	"image/color"
	"strings"

	"github.com/pkg/errors"
)

// AddColorToPalette adds c as the first color in p if not already there.
// Note that it does no additional checks, so callers must make sure
// that the palette is valid for the relevant format.
func AddColorToPalette(c color.Color, p color.Palette) color.Palette {
	var found bool
	for _, cc := range p {
		if c == cc {
			found = true
			break
		}
	}

	if !found {
		p = append(color.Palette{c}, p...)
	}

	return p
}

// ReplaceColorInPalette will replace the color in palette p closest to c in Euclidean
// R,G,B,A space with c.
func ReplaceColorInPalette(c color.Color, p color.Palette) {
	p[p.Index(c)] = c
}

func hexStringToColor(s string) (color.Color, error) {
	s = strings.TrimPrefix(s, "#")

	if len(s) != 3 && len(s) != 6 {
		return nil, errors.Errorf("invalid color code: %q", s)
	}

	s = strings.ToLower(s)

	if len(s) == 3 {
		var v string
		for _, r := range s {
			v += string(r) + string(r)
		}
		s = v
	}

	// Standard colors.
	if s == "ffffff" {
		return color.White, nil
	}

	if s == "000000" {
		return color.Black, nil
	}

	// Set Alfa to white.
	s += "ff"

	b, err := hex.DecodeString(s)
	if err != nil {
		return nil, err
	}

	return color.RGBA{b[0], b[1], b[2], b[3]}, nil

}