feat(distribution-banner): 分销站点轮播支持 PC/移动端分图与热区配置

2026-10-17 14:47:00 +08:00
parent ab9d852bde
commit 790267e3eb
9 changed files with 1472 additions and 120 deletions
@@ -0,0 +1,106 @@
+/**
+ * 图片透明区域探测：用于后台在上传「热区按钮图 / 海报底图」时提示
+ * 「这张图其实没有透明区域」——最常见的坑是把设计工具里带棋盘格的预览
+ * 截图/另存下来，棋盘格就成了真实像素，前台会照实显示。
+ */
+
+export interface ImageTransparencyProbe {
+  /** 是否存在透明像素（alpha < 250） */
+  hasTransparentPixels: boolean
+  /** 透明像素占比（0-1） */
+  transparentRatio: number
+  /** 不透明像素是否只有极少数浅灰/白颜色（棋盘格或纯色底烘焙进图片的典型特征） */
+  suspectedBakedBackdrop: boolean
+}
+
+const SAMPLE_MAX_SIDE = 160
+/** alpha 低于该值即视为透明像素 */
+const TRANSPARENT_ALPHA = 250
+/** 无明显透明像素的判定阈值（透明像素占比） */
+const NEGLIGIBLE_TRANSPARENT_RATIO = 0.002
+
+/** 纯像素分析（无 DOM 依赖，便于单测）。 */
+export function analyzeImagePixels(data: Uint8ClampedArray | number[]): ImageTransparencyProbe {
+  const total = Math.floor(data.length / 4)
+  if (total <= 0) {
+    return { hasTransparentPixels: false, transparentRatio: 0, suspectedBakedBackdrop: false }
+  }
+
+  let transparent = 0
+  let opaque = 0
+  let lightOnly = true
+  const colors = new Set<number>()
+
+  for (let index = 0; index < total; index += 1) {
+    const offset = index * 4
+    const r = data[offset] ?? 0
+    const g = data[offset + 1] ?? 0
+    const b = data[offset + 2] ?? 0
+    const a = data[offset + 3] ?? 0
+    if (a < TRANSPARENT_ALPHA) {
+      transparent += 1
+      continue
+    }
+    opaque += 1
+    const min = Math.min(r, g, b)
+    const max = Math.max(r, g, b)
+    if (min < 216 || max - min > 28) lightOnly = false
+    // 量化到 4bit/通道，避免抗锯齿噪点导致颜色数虚高
+    colors.add(((r >> 4) << 8) | ((g >> 4) << 4) | (b >> 4))
+  }
+
+  const transparentRatio = transparent / total
+  return {
+    hasTransparentPixels: transparentRatio > NEGLIGIBLE_TRANSPARENT_RATIO,
+    transparentRatio,
+    suspectedBakedBackdrop:
+      opaque > 0 &&
+      lightOnly &&
+      transparentRatio <= NEGLIGIBLE_TRANSPARENT_RATIO &&
+      colors.size <= 4,
+  }
+}
+
+/** 读取本地文件像素并分析；环境不支持时返回 null（不阻塞上传）。 */
+export async function probeImageTransparency(file: File): Promise<ImageTransparencyProbe | null> {
+  const source = await loadImageSource(file)
+  if (!source) return null
+  const width = Math.max(1, Math.round(source.width))
+  const height = Math.max(1, Math.round(source.height))
+  const scale = Math.min(1, SAMPLE_MAX_SIDE / Math.max(width, height))
+  const targetWidth = Math.max(1, Math.round(width * scale))
+  const targetHeight = Math.max(1, Math.round(height * scale))
+
+  const canvas = document.createElement('canvas')
+  canvas.width = targetWidth
+  canvas.height = targetHeight
+  const context = canvas.getContext('2d')
+  if (!context) return null
+  context.clearRect(0, 0, targetWidth, targetHeight)
+  context.drawImage(source as CanvasImageSource, 0, 0, targetWidth, targetHeight)
+  const imageData = context.getImageData(0, 0, targetWidth, targetHeight)
+  return analyzeImagePixels(imageData.data)
+}
+
+async function loadImageSource(file: File): Promise<ImageBitmap | HTMLImageElement | null> {
+  if (typeof createImageBitmap === 'function') {
+    try {
+      return await createImageBitmap(file)
+    } catch {
+      // 继续走 <img> 兜底
+    }
+  }
+  return await new Promise(resolve => {
+    const url = URL.createObjectURL(file)
+    const image = new Image()
+    image.onload = () => {
+      URL.revokeObjectURL(url)
+      resolve(image)
+    }
+    image.onerror = () => {
+      URL.revokeObjectURL(url)
+      resolve(null)
+    }
+    image.src = url
+  })
+}