github.com/linchen2chris/hugo@v0.0.0-20230307053224-cec209389705/resources/images/color.go (about)

     1  // Copyright 2019 The Hugo Authors. All rights reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  // http://www.apache.org/licenses/LICENSE-2.0
     7  //
     8  // Unless required by applicable law or agreed to in writing, software
     9  // distributed under the License is distributed on an "AS IS" BASIS,
    10  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package images
    15  
    16  import (
    17  	"encoding/hex"
    18  	"fmt"
    19  	"image/color"
    20  	"strings"
    21  )
    22  
    23  // AddColorToPalette adds c as the first color in p if not already there.
    24  // Note that it does no additional checks, so callers must make sure
    25  // that the palette is valid for the relevant format.
    26  func AddColorToPalette(c color.Color, p color.Palette) color.Palette {
    27  	var found bool
    28  	for _, cc := range p {
    29  		if c == cc {
    30  			found = true
    31  			break
    32  		}
    33  	}
    34  
    35  	if !found {
    36  		p = append(color.Palette{c}, p...)
    37  	}
    38  
    39  	return p
    40  }
    41  
    42  // ReplaceColorInPalette will replace the color in palette p closest to c in Euclidean
    43  // R,G,B,A space with c.
    44  func ReplaceColorInPalette(c color.Color, p color.Palette) {
    45  	p[p.Index(c)] = c
    46  }
    47  
    48  // ColorToHexString converts a color to a hex string.
    49  func ColorToHexString(c color.Color) string {
    50  	r, g, b, a := c.RGBA()
    51  	rgba := color.RGBA{uint8(r), uint8(g), uint8(b), uint8(a)}
    52  	return fmt.Sprintf("#%.2x%.2x%.2x", rgba.R, rgba.G, rgba.B)
    53  
    54  }
    55  
    56  func hexStringToColor(s string) (color.Color, error) {
    57  	s = strings.TrimPrefix(s, "#")
    58  
    59  	if len(s) != 3 && len(s) != 6 {
    60  		return nil, fmt.Errorf("invalid color code: %q", s)
    61  	}
    62  
    63  	s = strings.ToLower(s)
    64  
    65  	if len(s) == 3 {
    66  		var v string
    67  		for _, r := range s {
    68  			v += string(r) + string(r)
    69  		}
    70  		s = v
    71  	}
    72  
    73  	// Standard colors.
    74  	if s == "ffffff" {
    75  		return color.White, nil
    76  	}
    77  
    78  	if s == "000000" {
    79  		return color.Black, nil
    80  	}
    81  
    82  	// Set Alfa to white.
    83  	s += "ff"
    84  
    85  	b, err := hex.DecodeString(s)
    86  	if err != nil {
    87  		return nil, err
    88  	}
    89  
    90  	return color.RGBA{b[0], b[1], b[2], b[3]}, nil
    91  }