From fec812bc326eea6eda30a57f6feee90728926d05 Mon Sep 17 00:00:00 2001
From: Hill Ma <hillma@google.com>
Date: Wed, 9 Nov 2022 21:29:58 -0800
Subject: [PATCH] Add "fastgif" image type that provides much faster (but lower
 quality) GIF quantization.

The default image type is changed to PNG as it is the most "trouble free" choice.
---
 fastgif_lut.go | 260 +++++++++++++++++++++++++++++++++++++++++++++++++
 wrp.go         |  26 ++++-
 wrp.html       |   1 +
 3 files changed, 284 insertions(+), 3 deletions(-)
 create mode 100644 fastgif_lut.go

diff --git a/fastgif_lut.go b/fastgif_lut.go
new file mode 100644
index 0000000..9cd4b11
--- /dev/null
+++ b/fastgif_lut.go
@@ -0,0 +1,260 @@
+package main
+
+var FastGifLut = [256]int{
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	0,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	1,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	2,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	3,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	4,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+	5,
+}
diff --git a/wrp.go b/wrp.go
index 49d1931..85be069 100644
--- a/wrp.go
+++ b/wrp.go
@@ -15,6 +15,7 @@ import (
 	"fmt"
 	"html/template"
 	"image"
+	"image/color/palette"
 	"image/gif"
 	"image/png"
 	"io/ioutil"
@@ -129,7 +130,7 @@ func (rq *wrpReq) parseForm() {
 	rq.keys = rq.r.FormValue("k")
 	rq.buttons = rq.r.FormValue("Fn")
 	rq.imgType = rq.r.FormValue("t")
-	if rq.imgType != "gif" && rq.imgType != "png" {
+	if rq.imgType != "fastgif" && rq.imgType != "gif" && rq.imgType != "png" {
 		rq.imgType = defType
 	}
 	log.Printf("%s WrpReq from UI Form: %+v\n", rq.r.RemoteAddr, rq)
@@ -288,6 +289,8 @@ func (rq *wrpReq) capture() {
 	var ssize string
 	var iw, ih int
 	switch rq.imgType {
+	case "fastgif":
+		fallthrough
 	case "gif":
 		i, err := png.Decode(bytes.NewReader(pngcap))
 		if err != nil {
@@ -301,8 +304,25 @@ func (rq *wrpReq) capture() {
 		}
 		var gifbuf bytes.Buffer
 		st := time.Now()
-		q := median.Quantizer(rq.colors)
-		p := q.Paletted(i)
+		var p *image.Paletted
+		if rq.imgType == "fastgif" {
+			r := i.Bounds()
+			// NOTE: the color index computation below works only for palette.WebSafe!
+			p = image.NewPaletted(r, palette.WebSafe)
+			for y := 0; y != r.Dy(); y++ {
+				for x := 0; x != r.Dx(); x++ {
+					c := i.At(x, y)
+					r, g, b, _ := c.RGBA()
+					r6 := FastGifLut[r&0xff]
+					g6 := FastGifLut[g&0xff]
+					b6 := FastGifLut[b&0xff]
+					p.SetColorIndex(x, y, uint8(36*r6+6*g6+b6))
+				}
+			}
+		} else {
+			q := median.Quantizer(rq.colors)
+			p = q.Paletted(i)
+		}
 		err = gif.Encode(&gifbuf, p, &gif.Options{})
 		if err != nil {
 			log.Printf("%s Failed to encode GIF: %s\n", rq.r.RemoteAddr, err)
diff --git a/wrp.html b/wrp.html
index 58b4094..cbd72e3 100644
--- a/wrp.html
+++ b/wrp.html
@@ -21,6 +21,7 @@
                 <OPTION VALUE="1.3" {{ if eq .Zoom 1.3}}SELECTED{{end}}>1.3 x</OPTION>
             </SELECT>
             T <SELECT NAME="t">
+                <OPTION VALUE="fastgif" {{ if eq .ImgType "fastgif"}}SELECTED{{end}}>Fast GIF</OPTION>
                 <OPTION VALUE="gif" {{ if eq .ImgType "gif"}}SELECTED{{end}}>GIF</OPTION>
                 <OPTION VALUE="png" {{ if eq .ImgType "png"}}SELECTED{{end}}>PNG</OPTION>
             </SELECT>