feat(api): improve badge customization with dynamic text colors based on contrast

Author: sandros94

docs/content/2.guide/1.features.md

@@ -159,7 +159,7 @@ You can further customize your badges by appending query parameters to the badge
 
 ##### `labelColor`
 
-Overrides the default label color. You can pass a standard hex code (with or without the `#` prefix).
+Overrides the default label color. You can pass a standard hex code (with or without the `#` prefix). The label text color is automatically chosen (black or white) based on WCAG contrast ratio so the badge remains readable.
 
 - **Default**: `#0a0a0a`
 - **Usage**: `?labelColor=HEX_CODE`
@@ -173,16 +173,16 @@ Overrides the default label text. You can pass any string to customize the label
 
 ##### `color`
 
-Overrides the default strategy color. You can pass a standard hex code (with or without the `#` prefix).
+Overrides the default strategy color. You can pass a standard hex code (with or without the `#` prefix). The text color is automatically chosen (black or white) based on WCAG contrast ratio so the badge remains readable.
 
 - **Default**: Depends on the badge type (e.g., version is blue, downloads are orange).
 - **Usage**: `?color=HEX_CODE`
 
-| Example        | URL                                    |
-| :------------- | :------------------------------------- |
-| **Hot Pink**   | `.../badge/version/nuxt?colorB=ff69b4` |
-| **Pure Black** | `.../badge/version/nuxt?colorB=000000` |
-| **Brand Blue** | `.../badge/version/nuxt?colorB=3b82f6` |
+| Example        | URL                                   |
+| :------------- | :------------------------------------ |
+| **Hot Pink**   | `.../badge/version/nuxt?color=ff69b4` |
+| **Pure Black** | `.../badge/version/nuxt?color=000000` |
+| **Brand Blue** | `.../badge/version/nuxt?color=3b82f6` |
 
 ##### `name`
 

server/api/registry/badge/[type]/[...pkg].get.ts

@@ -95,6 +95,23 @@ function escapeXML(str: string): string {
     .replace(/"/g, '"')
 }
 
+function toLinear(c: number): number {
+  return c <= 0.04045 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4)
+}
+
+function getContrastTextColor(bgHex: string): string {
+  let clean = bgHex.replace('#', '')
+  if (clean.length === 3)
+    clean = clean[0]! + clean[0]! + clean[1]! + clean[1]! + clean[2]! + clean[2]!
+  if (!/^[0-9a-f]{6}$/i.test(clean)) return '#ffffff'
+  const r = parseInt(clean.slice(0, 2), 16) / 255
+  const g = parseInt(clean.slice(2, 4), 16) / 255
+  const b = parseInt(clean.slice(4, 6), 16) / 255
+  const luminance = 0.2126 * toLinear(r) + 0.7152 * toLinear(g) + 0.0722 * toLinear(b)
+  // threshold where contrast ratio with white equals contrast ratio with black
+  return luminance > 0.179 ? '#000000' : '#ffffff'
+}
+
 function measureShieldsTextLength(text: string): number {
   const measuredWidth = measureTextWidth(text, SHIELDS_FONT_SHORTHAND)
 
@@ -110,8 +127,11 @@ function renderDefaultBadgeSvg(params: {
   finalLabel: string
   finalLabelColor: string
   finalValue: string
+  labelTextColor: string
+  valueTextColor: string
 }): string {
-  const { finalColor, finalLabel, finalLabelColor, finalValue } = params
+  const { finalColor, finalLabel, finalLabelColor, finalValue, labelTextColor, valueTextColor } =
+    params
   const leftWidth = finalLabel.trim().length === 0 ? 0 : measureDefaultTextWidth(finalLabel)
   const rightWidth = measureDefaultTextWidth(finalValue)
   const totalWidth = leftWidth + rightWidth
@@ -120,19 +140,19 @@ function renderDefaultBadgeSvg(params: {
   const escapedValue = escapeXML(finalValue)
 
   return `
-    <svg xmlns="http://www.w3.org/2000/svg" width="${totalWidth}" height="${height}" role="img" aria-label="${escapedLabel}: ${escapedValue}">
-      <clipPath id="r">
-        <rect width="${totalWidth}" height="${height}" rx="3" fill="#fff"/>
-      </clipPath>
-      <g clip-path="url(#r)">
-        <rect width="${leftWidth}" height="${height}" fill="${finalLabelColor}"/>
-        <rect x="${leftWidth}" width="${rightWidth}" height="${height}" fill="${finalColor}"/>
-      </g>
-      <g text-anchor="middle" font-family="Geist, system-ui, -apple-system, sans-serif" font-size="11">
-        <text x="${leftWidth / 2}" y="14" fill="#ffffff">${escapedLabel}</text>
-        <text x="${leftWidth + rightWidth / 2}" y="14" fill="#ffffff">${escapedValue}</text>
-      </g>
-    </svg>
+<svg xmlns="http://www.w3.org/2000/svg" width="${totalWidth}" height="${height}" role="img" aria-label="${escapedLabel}: ${escapedValue}">
+  <clipPath id="r">
+    <rect width="${totalWidth}" height="${height}" rx="3" fill="#fff"/>
+  </clipPath>
+  <g clip-path="url(#r)">
+    <rect width="${leftWidth}" height="${height}" fill="${finalLabelColor}"/>
+    <rect x="${leftWidth}" width="${rightWidth}" height="${height}" fill="${finalColor}"/>
+  </g>
+  <g text-anchor="middle" font-family="Geist, system-ui, -apple-system, sans-serif" font-size="11">
+    <text x="${leftWidth / 2}" y="14" fill="${labelTextColor}">${escapedLabel}</text>
+    <text x="${leftWidth + rightWidth / 2}" y="14" fill="${valueTextColor}">${escapedValue}</text>
+  </g>
+</svg>
   `.trim()
 }
 
@@ -141,8 +161,11 @@ function renderShieldsBadgeSvg(params: {
   finalLabel: string
   finalLabelColor: string
   finalValue: string
+  labelTextColor: string
+  valueTextColor: string
 }): string {
-  const { finalColor, finalLabel, finalLabelColor, finalValue } = params
+  const { finalColor, finalLabel, finalLabelColor, finalValue, labelTextColor, valueTextColor } =
+    params
   const hasLabel = finalLabel.trim().length > 0
 
   const leftTextLength = hasLabel ? measureShieldsTextLength(finalLabel) : 0
@@ -174,11 +197,11 @@ function renderShieldsBadgeSvg(params: {
         <rect x="${leftWidth}" width="${rightWidth}" height="${height}" fill="${finalColor}"/>
         <rect width="${totalWidth}" height="${height}" fill="url(#s)"/>
       </g>
-      <g fill="#fff" text-anchor="middle" font-family="Verdana, Geneva, DejaVu Sans, sans-serif" text-rendering="geometricPrecision" font-size="110">
+      <g text-anchor="middle" font-family="Verdana, Geneva, DejaVu Sans, sans-serif" text-rendering="geometricPrecision" font-size="110">
         <text aria-hidden="true" x="${leftCenter}" y="150" fill="#010101" fill-opacity=".3" transform="scale(.1)" textLength="${leftTextLengthAttr}">${escapedLabel}</text>
-        <text x="${leftCenter}" y="140" transform="scale(.1)" fill="#fff" textLength="${leftTextLengthAttr}">${escapedLabel}</text>
+        <text x="${leftCenter}" y="140" transform="scale(.1)" fill="${labelTextColor}" textLength="${leftTextLengthAttr}">${escapedLabel}</text>
         <text aria-hidden="true" x="${rightCenter}" y="150" fill="#010101" fill-opacity=".3" transform="scale(.1)" textLength="${rightTextLengthAttr}">${escapedValue}</text>
-        <text x="${rightCenter}" y="140" transform="scale(.1)" fill="#fff" textLength="${rightTextLengthAttr}">${escapedValue}</text>
+        <text x="${rightCenter}" y="140" transform="scale(.1)" fill="${valueTextColor}" textLength="${rightTextLengthAttr}">${escapedValue}</text>
       </g>
     </svg>
   `.trim()
@@ -442,8 +465,18 @@ export default defineCachedEventHandler(
       const rawLabelColor = labelColor ?? defaultLabelColor
       const finalLabelColor = rawLabelColor.startsWith('#') ? rawLabelColor : `#${rawLabelColor}`
 
+      const labelTextColor = getContrastTextColor(finalLabelColor)
+      const valueTextColor = getContrastTextColor(finalColor)
+
       const renderFn = badgeStyle === 'shieldsio' ? renderShieldsBadgeSvg : renderDefaultBadgeSvg
-      const svg = renderFn({ finalColor, finalLabel, finalLabelColor, finalValue })
+      const svg = renderFn({
+        finalColor,
+        finalLabel,
+        finalLabelColor,
+        finalValue,
+        labelTextColor,
+        valueTextColor,
+      })
 
       setHeader(event, 'Content-Type', 'image/svg+xml')
       setHeader(

test/e2e/badge.spec.ts

@@ -118,6 +118,42 @@ test.describe('badge API', () => {
     expect(body).toContain(`fill="#${customColor}"`)
   })
 
+  test('light color produces dark text for contrast', async ({ page, baseURL }) => {
+    // FFDC3B is a bright yellow — should get #000000 text
+    const url = toLocalUrl(baseURL, '/api/registry/badge/version/nuxt?color=FFDC3B')
+    const { body } = await fetchBadge(page, url)
+
+    expect(body).toContain('fill="#ffffff">version')
+    expect(body).toContain('fill="#000000">v')
+  })
+
+  test('dark color keeps white text for contrast', async ({ page, baseURL }) => {
+    // 0a0a0a is near-black — should keep #ffffff text
+    const url = toLocalUrl(baseURL, '/api/registry/badge/version/nuxt?color=0a0a0a')
+    const { body } = await fetchBadge(page, url)
+
+    expect(body).toContain('fill="#ffffff">version')
+    expect(body).toContain('fill="#ffffff">v')
+  })
+
+  test('light labelColor produces dark label text for contrast', async ({ page, baseURL }) => {
+    // ffffff label background — should get #000000 label text
+    const url = toLocalUrl(baseURL, '/api/registry/badge/version/nuxt?labelColor=ffffff')
+    const { body } = await fetchBadge(page, url)
+
+    expect(body).toContain('fill="#000000">version')
+    expect(body).toContain('fill="#ffffff">v')
+  })
+
+  test('3-char hex color is handled correctly for contrast', async ({ page, baseURL }) => {
+    // CCC expands to CCCCCC — a light grey, should get dark text
+    const url = toLocalUrl(baseURL, '/api/registry/badge/version/nuxt?color=CCC')
+    const { body } = await fetchBadge(page, url)
+
+    expect(body).toContain('fill="#000000">version')
+    expect(body).toContain('fill="#ffffff">v')
+  })
+
   test('custom label parameter is applied to SVG', async ({ page, baseURL }) => {
     const customLabel = 'my-label'
     const url = toLocalUrl(baseURL, `/api/registry/badge/version/nuxt?label=${customLabel}`)