| // Copyright 2017 The Wuffs Authors. |
| // |
| // 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 |
| // |
| // https://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. |
| |
| // +build ignore |
| |
| package main |
| |
| // extract-palette-indexes.go extracts the 1-byte-per-pixel indexes and, for |
| // paletted images, the 4-byte-per-entry BGRA (premultiplied alpha) palette of |
| // a paletted or gray GIF and PNG image. It checks that the GIF and PNG encode |
| // equivalent images. |
| // |
| // Usage: go run extract-palette-indexes.go foo.gif foo.png |
| |
| import ( |
| "bytes" |
| "fmt" |
| "image" |
| "image/gif" |
| "image/png" |
| "io/ioutil" |
| "os" |
| "path/filepath" |
| ) |
| |
| func main() { |
| if err := main1(); err != nil { |
| os.Stderr.WriteString(err.Error() + "\n") |
| os.Exit(1) |
| } |
| } |
| |
| func main1() error { |
| baseFilename, bPalette, bIndexes := "", []byte(nil), []byte(nil) |
| for i, a := range os.Args[1:] { |
| b := a[:len(a)-len(filepath.Ext(a))] |
| palette, indexes, err := decode(a) |
| if err != nil { |
| return err |
| } |
| if i == 0 { |
| baseFilename, bPalette, bIndexes = b, palette, indexes |
| } else if baseFilename != b { |
| return fmt.Errorf("arguments do not have a common base path") |
| } else if !bytes.Equal(bPalette, palette) { |
| return fmt.Errorf("palettes are not equivalent") |
| } else if !bytes.Equal(bIndexes, indexes) { |
| return fmt.Errorf("indexes are not equivalent") |
| } |
| } |
| if bPalette != nil { |
| if err := ioutil.WriteFile(baseFilename+".palette", bPalette, 0644); err != nil { |
| return err |
| } |
| } |
| if bIndexes != nil { |
| if err := ioutil.WriteFile(baseFilename+".indexes", bIndexes, 0644); err != nil { |
| return err |
| } |
| } |
| return nil |
| } |
| |
| func decode(filename string) (palette []byte, indexes []byte, err error) { |
| f, err := os.Open(filename) |
| if err != nil { |
| return nil, nil, err |
| } |
| defer f.Close() |
| |
| m, err := image.Image(nil), error(nil) |
| switch ext := filepath.Ext(filename); ext { |
| case ".gif": |
| m, err = gif.Decode(f) |
| case ".png": |
| m, err = png.Decode(f) |
| default: |
| return nil, nil, fmt.Errorf("unsupported filename extension %q", ext) |
| } |
| if err != nil { |
| return nil, nil, err |
| } |
| switch m := m.(type) { |
| case *image.Gray: |
| return nil, m.Pix, nil |
| case *image.Paletted: |
| palette = make([]byte, 4*256) |
| allGray := true |
| for i, c := range m.Palette { |
| r, g, b, a := c.RGBA() |
| palette[4*i+0] = uint8(b >> 8) |
| palette[4*i+1] = uint8(g >> 8) |
| palette[4*i+2] = uint8(r >> 8) |
| palette[4*i+3] = uint8(a >> 8) |
| if allGray { |
| y := uint32(i) |
| allGray = r>>8 == y && g>>8 == y && b>>8 == y |
| } |
| } |
| if allGray { |
| return nil, m.Pix, nil |
| } |
| return palette, m.Pix, nil |
| } |
| return nil, nil, fmt.Errorf("decoded image type: got %T, want *image.Paletted", m) |
| } |