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image: introduce Decode and RegisterFormat.
R=r, rsc CC=golang-dev https://golang.org/cl/1849054
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@ -7,6 +7,7 @@ include ../../Make.$(GOARCH)
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TARG=image
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GOFILES=\
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color.go\
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format.go\
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image.go\
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names.go\
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73
src/pkg/image/format.go
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73
src/pkg/image/format.go
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@ -0,0 +1,73 @@
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// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package image
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import (
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"bufio"
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"io"
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"os"
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)
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// An UnknownFormatErr indicates that decoding encountered an unknown format.
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var UnknownFormatErr = os.NewError("image: unknown format")
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// A format holds an image format's name, magic header and how to decode it.
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type format struct {
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name, magic string
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decode func(io.Reader) (Image, os.Error)
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}
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// Formats is the list of registered formats.
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var formats []format
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// RegisterFormat registers an image format for use by Decode.
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// Name is the name of the format, like "jpeg" or "png".
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// Magic is the magic prefix that identifies the format's encoding.
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// Decode is the function that decodes the encoded image.
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func RegisterFormat(name, magic string, decode func(io.Reader) (Image, os.Error)) {
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n := len(formats)
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if n == cap(formats) {
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x := make([]format, n+1, 2*n+4)
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copy(x, formats)
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formats = x
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} else {
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formats = formats[0 : n+1]
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}
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formats[n] = format{name, magic, decode}
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}
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// A reader is an io.Reader that can also peek ahead.
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type reader interface {
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io.Reader
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Peek(int) ([]byte, os.Error)
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}
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// AsReader converts an io.Reader to a reader.
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func asReader(r io.Reader) reader {
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if rr, ok := r.(reader); ok {
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return rr
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}
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return bufio.NewReader(r)
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}
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// Decode decodes an image that has been encoded in a registered format.
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// Format registration is typically done by the init method of the codec-
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// specific package.
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func Decode(r io.Reader) (m Image, formatName string, err os.Error) {
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var f format
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rr := asReader(r)
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for _, g := range formats {
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s, err := rr.Peek(len(g.magic))
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if err == nil && string(s) == g.magic {
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f = g
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break
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}
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}
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if f.decode == nil {
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return nil, "", UnknownFormatErr
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}
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m, err = f.decode(rr)
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return m, f.name, err
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}
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@ -432,3 +432,7 @@ func Decode(r io.Reader) (image.Image, os.Error) {
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}
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return d.image, nil
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}
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func init() {
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image.RegisterFormat("jpeg", "\xff\xd8", Decode)
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}
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@ -464,3 +464,7 @@ func Decode(r io.Reader) (image.Image, os.Error) {
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}
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return d.image, nil
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}
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func init() {
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image.RegisterFormat("png", pngHeader, Decode)
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}
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