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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
/*
Package qr encodes QR codes.
*/
package qr
import (
"errors"
"image"
"image/color"
"github.com/mattermost/rsc/qr/coding"
)
// A Level denotes a QR error correction level.
// From least to most tolerant of errors, they are L, M, Q, H.
type Level int
const (
L Level = iota // 20% redundant
M // 38% redundant
Q // 55% redundant
H // 65% redundant
)
// Encode returns an encoding of text at the given error correction level.
func Encode(text string, level Level) (*Code, error) {
// Pick data encoding, smallest first.
// We could split the string and use different encodings
// but that seems like overkill for now.
var enc coding.Encoding
switch {
case coding.Num(text).Check() == nil:
enc = coding.Num(text)
case coding.Alpha(text).Check() == nil:
enc = coding.Alpha(text)
default:
enc = coding.String(text)
}
// Pick size.
l := coding.Level(level)
var v coding.Version
for v = coding.MinVersion; ; v++ {
if v > coding.MaxVersion {
return nil, errors.New("text too long to encode as QR")
}
if enc.Bits(v) <= v.DataBytes(l)*8 {
break
}
}
// Build and execute plan.
p, err := coding.NewPlan(v, l, 0)
if err != nil {
return nil, err
}
cc, err := p.Encode(enc)
if err != nil {
return nil, err
}
// TODO: Pick appropriate mask.
return &Code{cc.Bitmap, cc.Size, cc.Stride, 8}, nil
}
// A Code is a square pixel grid.
// It implements image.Image and direct PNG encoding.
type Code struct {
Bitmap []byte // 1 is black, 0 is white
Size int // number of pixels on a side
Stride int // number of bytes per row
Scale int // number of image pixels per QR pixel
}
// Black returns true if the pixel at (x,y) is black.
func (c *Code) Black(x, y int) bool {
return 0 <= x && x < c.Size && 0 <= y && y < c.Size &&
c.Bitmap[y*c.Stride+x/8]&(1<<uint(7-x&7)) != 0
}
// Image returns an Image displaying the code.
func (c *Code) Image() image.Image {
return &codeImage{c}
}
// codeImage implements image.Image
type codeImage struct {
*Code
}
var (
whiteColor color.Color = color.Gray{0xFF}
blackColor color.Color = color.Gray{0x00}
)
func (c *codeImage) Bounds() image.Rectangle {
d := (c.Size + 8) * c.Scale
return image.Rect(0, 0, d, d)
}
func (c *codeImage) At(x, y int) color.Color {
if c.Black(x, y) {
return blackColor
}
return whiteColor
}
func (c *codeImage) ColorModel() color.Model {
return color.GrayModel
}
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