Add support for SVG identicons

README.adoc

@@ -34,6 +34,8 @@ The latter resembles the color scheme used by GitHub.
 
 The request query parameter `d` can be used to request GitHub like patterns by setting the value to `github`.
 
+Using query param `ct` with value `svg` or using request header `Accept: image/svg+xml` will generate SVG identicon.
+
 ==== Examples
 
 Some examples for `/avatar/example` and different params.

icons/ghicons.go

@@ -42,6 +42,29 @@ func (generator *GhIconGenerator) GenIcon(id string, size int) *image.NRGBA {
 	return drawImage(mirrorData(data, blocks), blocks, size, generator.colorGenerator(hash))
 }
 
+func (generator *GhIconGenerator) GenSvg(id string, size int) string {
+	if size > 512 {
+		size = 512
+	}
+	blocks := 5
+
+	hash := HashBytes(id)
+	nibbles := nibbles(hash)
+	data := make([]bool, blocks*blocks)
+
+	for x := 0; x < blocks; x++ {
+		for y := 0; y < blocks; y++ {
+			ni := x + blocks*(blocks-y-1)
+			if x+blocks*y >= 2*blocks {
+				di := (x + blocks*y) - 2*blocks
+				data[di] = nibbles[ni%32]%2 == 0
+			}
+		}
+	}
+
+	return drawSvg(mirrorData(data, blocks), blocks, size, generator.colorGenerator(hash))
+}
+
 // https://processing.org/reference/map_.html
 func remap(value uint32, vmin uint32, vmax uint32, dmin uint32, dmax uint32) float32 {
 	return float32((value-vmin)*(dmax-dmin)) / float32((vmax-vmin)+dmin)

icons/icons.go

@@ -3,6 +3,7 @@ package icons
 import (
 	"crypto/md5"
 	"encoding/hex"
+	"fmt"
 	"image"
 	"image/color"
 	"image/draw"
@@ -12,6 +13,7 @@ import (
 
 type IconGenerator interface {
 	GenIcon(id string, size int) *image.NRGBA
+	GenSvg(id string, size int) string
 }
 
 func HashBytes(id string) [16]byte {
@@ -62,5 +64,37 @@ func drawImage(data []bool, blocks int, size int, c color.Color) *image.NRGBA {
 		}
 	}
 
+	drawSvg(data, blocks, size, c)
+
 	return img
 }
+
+func drawSvg(data []bool, blocks int, size int, c color.Color) string {
+
+	blockSize := size / (blocks + 1)
+	border := (size - (blocks * blockSize)) / 2
+	r, g, b, _ := c.RGBA()
+	colorHtml := fmt.Sprintf("#%x%x%x", r>>8, g>>8, b>>8)
+
+	blockElems := fmt.Sprintf("<rect style=\"fill:#f0f0f0\" width=\"%d\" height=\"%d\" x=\"0\" y=\"0\" />", size, size)
+
+	for x := 0; x < blocks; x++ {
+		for y := 0; y < blocks; y++ {
+			idx := x*blocks + y
+			if data[idx] {
+				blockElems += fmt.Sprintf(
+					`<rect style="fill:%s" width="%d" height="%d" x="%d" y="%d" />`,
+					colorHtml,
+					blockSize,
+					blockSize,
+					border+(x*blockSize),
+					border+(y*blockSize))
+			}
+		}
+	}
+
+	return fmt.Sprintf(`<?xml version="1.0" encoding="UTF-8"?>
+<svg width="%d" height="%d" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:svg="http://www.w3.org/2000/svg"><g>%s</g></svg>`,
+		size, size,
+		blockElems)
+}

icons/idicons.go

@@ -34,6 +34,21 @@ func (generator *IdIconGenerator) GenIcon(id string, size int) *image.NRGBA {
 	return drawImage(mirrorData(data, blocks), blocks, size, generator.colorGenerator(hash))
 }
 
+func (generator *IdIconGenerator) GenSvg(id string, size int) string {
+	id = strings.ToLower(id)
+	blocks := 5
+	if size > 512 {
+		size = 512
+	}
+
+	hash := HashBytes(id)
+	data := make([]bool, blocks*blocks)
+	for i := 0; i < len(hash)-1; i++ {
+		data[i] = hash[i]%2 != hash[i+1]%2
+	}
+	return drawSvg(mirrorData(data, blocks), blocks, size, generator.colorGenerator(hash))
+}
+
 func ColorV1(hash [16]byte) color.RGBA {
 	r := 32 + (hash[0]%16)/2<<4
 	g := 32 + (hash[2]%16)/2<<4

idicon.go

@@ -62,7 +62,6 @@ func requestHandler(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	w.Header().Add("Content-Type", "image/png")
 	cFunc := icons.ColorV2
 	if colorScheme == "v1" {
 		cFunc = icons.ColorV1
@@ -77,7 +76,15 @@ func requestHandler(w http.ResponseWriter, r *http.Request) {
 		iconGenerator = icons.NewIdIconGenerator().WithColorGenerator(cFunc)
 	}
 
-	err = png.Encode(w, iconGenerator.GenIcon(id, size))
+	ct := r.URL.Query().Get("ct")
+	cth := r.Header.Get("Accept")
+	if ct == "svg" || cth == "image/svg+xml" {
+		w.Header().Add("Content-Type", "image/svg+xml")
+		_, err = w.Write([]byte(iconGenerator.GenSvg(id, size)))
+	} else {
+		w.Header().Add("Content-Type", "image/png")
+		err = png.Encode(w, iconGenerator.GenIcon(id, size))
+	}
 }
 
 var (

static/index.html

@@ -108,18 +108,18 @@
             width: 90%;
         }
 
-        #size-input, #color-input, #type-input {
+        #size-input, #color-input, #type-input, #contenttype-input {
             display: flex;
             flex-direction: column;
             margin: 0 auto;
         }
 
-        #size-input > input, #color-input > select, #type-input > select {
+        #size-input > input, #color-input > select, #type-input > select, #contenttype-input > select {
             width: 8em;
         }
 
         #settings {
-            grid-template-columns: repeat(3, 1fr);
+            grid-template-columns: repeat(4, 1fr);
             display: grid;
         }
 
@@ -185,6 +185,13 @@
                     <option value="gh" selected>GH</option>
                 </select>
             </div>
+            <div id="contenttype-input" class="small">
+                <label for="contenttype">Content-Type</label>
+                <select id="contenttype" onchange="newcontenttype(this.value)">
+                    <option value="png" selected>PNG</option>
+                    <option value="svg">SVG</option>
+                </select>
+            </div>
         </fieldset>
         <fieldset id="actions">
             <legend>Actions</legend>
@@ -212,6 +219,7 @@
     let currentsize = document.getElementById('size').value;
     let currentcolor = document.getElementById('color').value;
     let currenttype = document.getElementById('type').value;
+    let currentcontenttype = document.getElementById('contenttype').value;
     idicon(document.getElementById('value').value);
 
     function fetchGhId() {
@@ -253,12 +261,17 @@
         idicon(document.getElementById('value').value);
     }
 
+    function newcontenttype(value) {
+        currentcontenttype = value;
+        idicon(document.getElementById('value').value);
+    }
+
     function idicon(value) {
         if (value.trim() === '') {
             document.getElementById('idicon').src = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAC0lEQVQI12NgAAIAAAUAAeImBZsAAAAASUVORK5CYII=';
             return;
         }
-        document.getElementById('idicon').src = `./avatar/${value}?s=${currentsize}&c=${currentcolor}&d=${currenttype}`
+        document.getElementById('idicon').src = `./avatar/${value}?s=${currentsize}&c=${currentcolor}&d=${currenttype}&ct=${currentcontenttype}`
     }
 </script>
 </html>