From 67b09086b49f1ae83cf37e9d1ec70db07ebf1f8d Mon Sep 17 00:00:00 2001
From: mappu <mappu04@gmail.com>
Date: Thu, 24 Nov 2016 20:54:21 +1300
Subject: [PATCH] cmd/gopngquant: working implementation

---
 cmd/gopngquant/main.go | 45 ++++++++++++++++++++++++++++++------------
 1 file changed, 32 insertions(+), 13 deletions(-)

diff --git a/cmd/gopngquant/main.go b/cmd/gopngquant/main.go
index edb80e6..034c98a 100644
--- a/cmd/gopngquant/main.go
+++ b/cmd/gopngquant/main.go
@@ -4,6 +4,7 @@ import (
 	"flag"
 	"fmt"
 	"image"
+	"image/color"
 	"image/png"
 	"os"
 
@@ -15,14 +16,36 @@ func GoImageToRgba32(im image.Image) []byte {
 	h := im.Bounds().Max.Y
 	ret := make([]byte, w*h*4)
 
+	p := 0
+
 	for y := 0; y < h; y += 1 {
 		for x := 0; x < w; x += 1 {
 			r16, g16, b16, a16 := im.At(x, y).RGBA() // Each value ranges within [0, 0xffff]
 
-			ret[y*h+x+0] = uint8(r16 >> 8)
-			ret[y*h+x+1] = uint8(g16 >> 8)
-			ret[y*h+x+2] = uint8(b16 >> 8)
-			ret[y*h+x+3] = uint8(a16 >> 8)
+			ret[p+0] = uint8(r16 >> 8)
+			ret[p+1] = uint8(g16 >> 8)
+			ret[p+2] = uint8(b16 >> 8)
+			ret[p+3] = uint8(a16 >> 8)
+			p += 4
+		}
+	}
+
+	return ret
+}
+
+func Rgb8PaletteToGoImage(w, h int, rgb8data []byte, pal color.Palette) image.Image {
+	rect := image.Rectangle{
+		Max: image.Point{
+			X: w,
+			Y: h,
+		},
+	}
+
+	ret := image.NewPaletted(rect, pal)
+
+	for y := 0; y < h; y += 1 {
+		for x := 0; x < w; x += 1 {
+			ret.SetColorIndex(x, y, rgb8data[y*h+x])
 		}
 	}
 
@@ -42,6 +65,9 @@ func Crush(sourcefile, destfile string) error {
 		return fmt.Errorf("png.Decode: %s", err.Error())
 	}
 
+	width := img.Bounds().Max.X
+	height := img.Bounds().Max.Y
+
 	attr, err := imagequant.NewAttributes()
 	if err != nil {
 		return fmt.Errorf("NewAttributes: %s", err.Error())
@@ -50,7 +76,7 @@ func Crush(sourcefile, destfile string) error {
 
 	rgba32data := GoImageToRgba32(img)
 
-	iqm, err := imagequant.NewImage(attr, string(rgba32data), img.Bounds().Max.X, img.Bounds().Max.Y, 0)
+	iqm, err := imagequant.NewImage(attr, string(rgba32data), width, height, 0)
 	if err != nil {
 		return fmt.Errorf("NewImage: %s", err.Error())
 	}
@@ -67,14 +93,7 @@ func Crush(sourcefile, destfile string) error {
 		return fmt.Errorf("WriteRemappedImage: %s", err.Error())
 	}
 
-	rect := image.Rectangle{Max: image.Point{X: res.GetImageWidth(), Y: res.GetImageHeight()}}
-	pal := res.GetPalette()
-	im2 := image.NewPaletted(rect, pal)
-	for y := 0; y < rect.Max.Y; y += 1 {
-		for x := 0; x < rect.Max.X; x += 1 {
-			im2.Set(x, y, pal[rgb8data[y*rect.Max.Y+x]])
-		}
-	}
+	im2 := Rgb8PaletteToGoImage(res.GetImageWidth(), res.GetImageHeight(), rgb8data, res.GetPalette())
 
 	fh2, err := os.OpenFile(destfile, os.O_WRONLY|os.O_CREATE, 0644)
 	if err != nil {