convert png boards to gif

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/dop251/goja v0.0.0-20230122112309-96b1610dd4f7
 	github.com/dsoprea/go-exif/v3 v3.0.0-20221012082141-d21ac8e2de85
 	github.com/dsoprea/go-png-image-structure/v2 v2.0.0-20210512210324-29b889a6093d
+	github.com/ericpauley/go-quantize v0.0.0-20200331213906-ae555eb2afa4
 	github.com/fsnotify/fsnotify v1.6.0
 	github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0
 	github.com/jung-kurt/gofpdf v1.16.2

go.sum

@@ -60,6 +60,8 @@ github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymF
 github.com/envoyproxy/go-control-plane v0.9.1-0.20191026205805-5f8ba28d4473/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.4/go.mod h1:6rpuAdCZL397s3pYoYcLgu1mIlRU8Am5FuJP05cCM98=
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
+github.com/ericpauley/go-quantize v0.0.0-20200331213906-ae555eb2afa4 h1:BBade+JlV/f7JstZ4pitd4tHhpN+w+6I+LyOS7B4fyU=
+github.com/ericpauley/go-quantize v0.0.0-20200331213906-ae555eb2afa4/go.mod h1:H7chHJglrhPPzetLdzBleF8d22WYOv7UM/lEKYiwlKM=
 github.com/fatih/color v1.13.0 h1:8LOYc1KYPPmyKMuN8QV2DNRWNbLo6LZ0iLs8+mlH53w=
 github.com/fatih/color v1.13.0/go.mod h1:kLAiJbzzSOZDVNGyDpeOxJ47H46qBXwg5ILebYFFOfk=
 github.com/fsnotify/fsnotify v1.6.0 h1:n+5WquG0fcWoWp6xPWfHdbskMCQaFnG6PfBrh1Ky4HY=

lib/xgif/xgif.go

@@ -0,0 +1,56 @@
+package xgif
+
+import (
+	"bytes"
+	"fmt"
+	"image"
+	"image/gif"
+	"image/png"
+
+	"github.com/ericpauley/go-quantize/quantize"
+)
+
+const INFINITE_LOOP = 0
+
+func AnimatePNGs(pngs [][]byte, gifWidth, gifHeight int, animIntervalMs int) ([]byte, error) {
+	interval := animIntervalMs / 10 // gif animation interval is in 100ths of a second
+	anim := &gif.GIF{
+		LoopCount: INFINITE_LOOP,
+		Config: image.Config{
+			Width:  gifWidth,
+			Height: gifHeight,
+		},
+	}
+
+	for _, pngBytes := range pngs {
+		pngImage, err := png.Decode(bytes.NewBuffer(pngBytes))
+		if err != nil {
+			return nil, err
+		}
+		buf := bytes.NewBuffer(nil)
+		err = gif.Encode(buf, pngImage, &gif.Options{
+			NumColors: 256, // GIFs can have up to 256 colors
+			Quantizer: quantize.MedianCutQuantizer{},
+		})
+		if err != nil {
+			return nil, err
+		}
+		gifImg, err := gif.Decode(buf)
+		if err != nil {
+			return nil, err
+		}
+		palettedImg, ok := gifImg.(*image.Paletted)
+		if !ok {
+			return nil, fmt.Errorf("decoded git image could not be cast as *image.Paletted")
+		}
+		anim.Image = append(anim.Image, palettedImg)
+		anim.Delay = append(anim.Delay, interval)
+	}
+
+	buf := bytes.NewBuffer(nil)
+	err := gif.EncodeAll(buf, anim)
+	if err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}

lib/xgif/xgif_test.go

@@ -0,0 +1,39 @@
+package xgif
+
+import (
+	"bytes"
+	_ "embed"
+	"image/png"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"oss.terrastruct.com/util-go/go2"
+)
+
+//go:embed test_input1.png
+var test_input1 []byte
+
+//go:embed test_input2.png
+var test_input2 []byte
+
+//go:embed test_output.gif
+var test_output []byte
+
+func TestPngToGif(t *testing.T) {
+	board1, err := png.Decode(bytes.NewBuffer(test_input1))
+	assert.NoError(t, err)
+	gifWidth := board1.Bounds().Dx()
+	gifHeight := board1.Bounds().Dy()
+
+	board2, err := png.Decode(bytes.NewBuffer(test_input2))
+	assert.NoError(t, err)
+	gifWidth = go2.Max(board2.Bounds().Dx(), gifWidth)
+	gifHeight = go2.Max(board2.Bounds().Dy(), gifHeight)
+
+	boards := [][]byte{test_input1, test_input2}
+	interval := 1_000
+	gifBytes, err := AnimatePNGs(boards, gifWidth, gifHeight, interval)
+	assert.NoError(t, err)
+
+	assert.Equal(t, test_output, gifBytes)
+}