Image is scaled down

gif_test.go

@@ -0,0 +1,65 @@
+// 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
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/gif"
+	"io"
+	"os"
+	"testing"
+)
+
+func TestGIF(t *testing.T) {
+	c, err := Encode("hello, world", L)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var buf bytes.Buffer
+	if err := encodeGIF(&buf, c.Image()); err != nil {
+		t.Fatal(err)
+	}
+	gifdat := buf.Bytes()
+	if true {
+		os.WriteFile("x.gif", gifdat, 0666)
+	}
+	m, err := gif.Decode(bytes.NewBuffer(gifdat))
+	if err != nil {
+		t.Fatal(err)
+	}
+	gm := m.(*image.Paletted)
+
+	scale := c.Scale
+	siz := c.Size
+	nbad := 0
+	for y := 0; y < scale*(8+siz); y++ {
+		for x := 0; x < scale*(8+siz); x++ {
+			v := byte(255)
+			if c.Black(x/scale-4, y/scale-4) {
+				v = 0
+			}
+			if gv := gm.At(x, y).(color.RGBA).R; gv != v {
+				t.Errorf("%d,%d = %d, want %d", x, y, gv, v)
+				if nbad++; nbad >= 20 {
+					t.Fatalf("too many bad pixels")
+				}
+			}
+		}
+	}
+}
+
+type bwQuantizer struct{}
+
+func (bwQuantizer) Quantize(p color.Palette, m image.Image) color.Palette {
+	if len(p) >= 2 {
+		return p
+	}
+	return append(p[:0], color.Black, color.White)
+}
+func encodeGIF(w io.Writer, m image.Image) error {
+	return gif.Encode(w, m, &gif.Options{NumColors: 2, Quantizer: bwQuantizer{}})
+}

qr.go

@@ -65,7 +65,7 @@ func Encode(text string, level Level) (*Code, error) {
 
 	// TODO: Pick appropriate mask.
 
-	return &Code{cc.Bitmap, cc.Size, cc.Stride, 8}, nil
+	return &Code{Bitmap: cc.Bitmap, Size: cc.Size, Stride: cc.Stride, Scale: 8}, nil
 }
 
 // A Code is a square pixel grid.
@@ -99,13 +99,15 @@ var (
 	blackColor color.Color = color.Gray{0x00}
 )
 
+const offset = 8
+
 func (c *codeImage) Bounds() image.Rectangle {
-	d := (c.Size + 8) * c.Scale
+	d := (c.Size + offset) * c.Scale
 	return image.Rect(0, 0, d, d)
 }
 
 func (c *codeImage) At(x, y int) color.Color {
-	if c.Black(x, y) {
+	if c.Black(x/c.Scale-offset/2, y/c.Scale-offset/2) {
 		return blackColor
 	}
 	return whiteColor