First commit

.gitignore

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+majokko
+test.png
+test.zng
+test.jpg

LICENSE

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+Copyright (C) 2022-2023 Ronsor Labs
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# Majokko
+
+`majokko` is intended to be a lightweight ImageMagick `convert` and
+`identify` alternative written in Go. The underlying library, found
+in the `henshin/` directory, can be reused by other programs.
+
+**This software is still in alpha, and as such, we do not commit to
+providing a stable API.**
+
+## Supported Formats
+
+```
++--- (D)ecode
+|+-- (E)ncode
+||+- (M)etadata wrangling
+|||  == Format ==
+DE-  JPEG
+DEM  PNG
+DEM  ZNG (Zstd PNG)
+DE-  GIF[1]
+DEM  NetPBM (PPM, PGM, etc.)
+DE-  JPEG XL[2][3]
+DE-  QOI (Quite OK Image format)
+D--  WEBP
+
+[1] Animated GIFs are not yet supported.
+[2] Requires external `cjxl` and `djxl` binaries. Enable with the
+`--enable-external-codecs` option.
+[3] Format not yet supported.
+```
+
+## License and Copyright Notice
+
+Copyright © 2022-2023 Ronsor Labs.
+
+This software is provided to you under the terms of the MIT license.
+See the included `LICENSE` file for more information.

format/png/README.md

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+# format/png
+
+This version of `image/png` has been modified to support reading and writing
+custom chunks (e.g. `tEXt` data).
+
+## License and Copyright Notice
+
+Copyright © 2009 The Go Authors  
+Copyright © 2022 Ronsor Labs

format/png/example_test.go

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+// Copyright 2016 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 png_test
+
+import (
+	"encoding/base64"
+	"fmt"
+	"image"
+	"image/color"
+	"image/png"
+	"io"
+	"log"
+	"os"
+	"strings"
+)
+
+const gopher = `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`
+
+// gopherPNG creates an io.Reader by decoding the base64 encoded image data string in the gopher constant.
+func gopherPNG() io.Reader { return base64.NewDecoder(base64.StdEncoding, strings.NewReader(gopher)) }
+
+func ExampleDecode() {
+	// This example uses png.Decode which can only decode PNG images.
+	// Consider using the general image.Decode as it can sniff and decode any registered image format.
+	img, err := png.Decode(gopherPNG())
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	levels := []string{" ", "░", "▒", "▓", "█"}
+
+	for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ {
+		for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ {
+			c := color.GrayModel.Convert(img.At(x, y)).(color.Gray)
+			level := c.Y / 51 // 51 * 5 = 255
+			if level == 5 {
+				level--
+			}
+			fmt.Print(levels[level])
+		}
+		fmt.Print("\n")
+	}
+}
+
+func ExampleEncode() {
+	const width, height = 256, 256
+
+	// Create a colored image of the given width and height.
+	img := image.NewNRGBA(image.Rect(0, 0, width, height))
+
+	for y := 0; y < height; y++ {
+		for x := 0; x < width; x++ {
+			img.Set(x, y, color.NRGBA{
+				R: uint8((x + y) & 255),
+				G: uint8((x + y) << 1 & 255),
+				B: uint8((x + y) << 2 & 255),
+				A: 255,
+			})
+		}
+	}
+
+	f, err := os.Create("image.png")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if err := png.Encode(f, img); err != nil {
+		f.Close()
+		log.Fatal(err)
+	}
+
+	if err := f.Close(); err != nil {
+		log.Fatal(err)
+	}
+}

format/png/paeth.go

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+// Copyright 2012 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 png
+
+// intSize is either 32 or 64.
+const intSize = 32 << (^uint(0) >> 63)
+
+func abs(x int) int {
+	// m := -1 if x < 0. m := 0 otherwise.
+	m := x >> (intSize - 1)
+
+	// In two's complement representation, the negative number
+	// of any number (except the smallest one) can be computed
+	// by flipping all the bits and add 1. This is faster than
+	// code with a branch.
+	// See Hacker's Delight, section 2-4.
+	return (x ^ m) - m
+}
+
+// paeth implements the Paeth filter function, as per the PNG specification.
+func paeth(a, b, c uint8) uint8 {
+	// This is an optimized version of the sample code in the PNG spec.
+	// For example, the sample code starts with:
+	//	p := int(a) + int(b) - int(c)
+	//	pa := abs(p - int(a))
+	// but the optimized form uses fewer arithmetic operations:
+	//	pa := int(b) - int(c)
+	//	pa = abs(pa)
+	pc := int(c)
+	pa := int(b) - pc
+	pb := int(a) - pc
+	pc = abs(pa + pb)
+	pa = abs(pa)
+	pb = abs(pb)
+	if pa <= pb && pa <= pc {
+		return a
+	} else if pb <= pc {
+		return b
+	}
+	return c
+}
+
+// filterPaeth applies the Paeth filter to the cdat slice.
+// cdat is the current row's data, pdat is the previous row's data.
+func filterPaeth(cdat, pdat []byte, bytesPerPixel int) {
+	var a, b, c, pa, pb, pc int
+	for i := 0; i < bytesPerPixel; i++ {
+		a, c = 0, 0
+		for j := i; j < len(cdat); j += bytesPerPixel {
+			b = int(pdat[j])
+			pa = b - c
+			pb = a - c
+			pc = abs(pa + pb)
+			pa = abs(pa)
+			pb = abs(pb)
+			if pa <= pb && pa <= pc {
+				// No-op.
+			} else if pb <= pc {
+				a = b
+			} else {
+				a = c
+			}
+			a += int(cdat[j])
+			a &= 0xff
+			cdat[j] = uint8(a)
+			c = b
+		}
+	}
+}

format/png/paeth_test.go

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+// Copyright 2012 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 png
+
+import (
+	"bytes"
+	"math/rand"
+	"testing"
+)
+
+func slowAbs(x int) int {
+	if x < 0 {
+		return -x
+	}
+	return x
+}
+
+// slowPaeth is a slow but simple implementation of the Paeth function.
+// It is a straight port of the sample code in the PNG spec, section 9.4.
+func slowPaeth(a, b, c uint8) uint8 {
+	p := int(a) + int(b) - int(c)
+	pa := slowAbs(p - int(a))
+	pb := slowAbs(p - int(b))
+	pc := slowAbs(p - int(c))
+	if pa <= pb && pa <= pc {
+		return a
+	} else if pb <= pc {
+		return b
+	}
+	return c
+}
+
+// slowFilterPaeth is a slow but simple implementation of func filterPaeth.
+func slowFilterPaeth(cdat, pdat []byte, bytesPerPixel int) {
+	for i := 0; i < bytesPerPixel; i++ {
+		cdat[i] += paeth(0, pdat[i], 0)
+	}
+	for i := bytesPerPixel; i < len(cdat); i++ {
+		cdat[i] += paeth(cdat[i-bytesPerPixel], pdat[i], pdat[i-bytesPerPixel])
+	}
+}
+
+func TestPaeth(t *testing.T) {
+	for a := 0; a < 256; a += 15 {
+		for b := 0; b < 256; b += 15 {
+			for c := 0; c < 256; c += 15 {
+				got := paeth(uint8(a), uint8(b), uint8(c))
+				want := slowPaeth(uint8(a), uint8(b), uint8(c))
+				if got != want {
+					t.Errorf("a, b, c = %d, %d, %d: got %d, want %d", a, b, c, got, want)
+				}
+			}
+		}
+	}
+}
+
+func BenchmarkPaeth(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		paeth(uint8(i>>16), uint8(i>>8), uint8(i))
+	}
+}
+
+func TestPaethDecode(t *testing.T) {
+	pdat0 := make([]byte, 32)
+	pdat1 := make([]byte, 32)
+	pdat2 := make([]byte, 32)
+	cdat0 := make([]byte, 32)
+	cdat1 := make([]byte, 32)
+	cdat2 := make([]byte, 32)
+	r := rand.New(rand.NewSource(1))
+	for bytesPerPixel := 1; bytesPerPixel <= 8; bytesPerPixel++ {
+		for i := 0; i < 100; i++ {
+			for j := range pdat0 {
+				pdat0[j] = uint8(r.Uint32())
+				cdat0[j] = uint8(r.Uint32())
+			}
+			copy(pdat1, pdat0)
+			copy(pdat2, pdat0)
+			copy(cdat1, cdat0)
+			copy(cdat2, cdat0)
+			filterPaeth(cdat1, pdat1, bytesPerPixel)
+			slowFilterPaeth(cdat2, pdat2, bytesPerPixel)
+			if !bytes.Equal(cdat1, cdat2) {
+				t.Errorf("bytesPerPixel: %d\npdat0: % x\ncdat0: % x\ngot:   % x\nwant:  % x", bytesPerPixel, pdat0, cdat0, cdat1, cdat2)
+				break
+			}
+		}
+	}
+}