From d5cfaa4605f256a18712bd03aee159e5a16533a8 Mon Sep 17 00:00:00 2001
From: douboer <douboer@gmail.com>
Date: Sat, 7 Feb 2026 15:05:34 +0800
Subject: [PATCH] update at 2026-02-07 15:05:34

---
 frontend/src/components/SvgPreview.vue | 188 +++++++++++++++++++++++--
 1 file changed, 180 insertions(+), 8 deletions(-)

diff --git a/frontend/src/components/SvgPreview.vue b/frontend/src/components/SvgPreview.vue
index 20d6c6b..ddf4ec2 100644
--- a/frontend/src/components/SvgPreview.vue
+++ b/frontend/src/components/SvgPreview.vue
@@ -1,9 +1,10 @@
 <script setup lang="ts">
-import { ref, computed, watch, onBeforeUnmount } from 'vue'
+import { ref, computed, watch, onBeforeUnmount, nextTick } from 'vue'
 import { useFontStore } from '../stores/fontStore'
 import { useUiStore } from '../stores/uiStore'
 import { generateSvg } from '../utils/svg-builder'
 import type { PreviewItem as PreviewItemType } from '../types/font'
+import type { SvgGenerateResult, FontInfo } from '../types/font'
 
 const fontStore = useFontStore()
 const uiStore = useUiStore()
@@ -17,13 +18,29 @@ const fontSize = computed(() => uiStore.fontSize)
 const fillColor = computed(() => uiStore.textColor)
 const PREVIEW_DEBOUNCE_MS = 240
 const PREVIEW_CONCURRENCY = 4
+const PREVIEW_GEOMETRY_CACHE_LIMIT = 600
+const PREVIEW_COLOR_TOKEN = '__FONT2SVG_FILL__'
+const PREVIEW_BATCH_SIZE = 20
+const PREVIEW_PREFETCH_OFFSET = 10
 let previewGenerateTimer: ReturnType<typeof setTimeout> | null = null
 let previewGenerationToken = 0
 let hasTriggeredInitialGenerate = false
+let previewLazyLoadObserver: IntersectionObserver | null = null
+const previewGeometryCache = new Map<string, Omit<SvgGenerateResult, 'svg'> & { svgTemplate: string }>()
+const renderedPreviewCount = ref(0)
+const previewTriggerItemEl = ref<HTMLElement | null>(null)
 
 const isAllPreviewSelected = computed(() => {
   return previewItems.value.length > 0 && previewItems.value.every(item => item.selected)
 })
+const hasMorePreviewItems = computed(() => renderedPreviewCount.value < previewItems.value.length)
+const visiblePreviewItems = computed(() => previewItems.value.slice(0, renderedPreviewCount.value))
+const previewTriggerIndex = computed(() => {
+  if (!hasMorePreviewItems.value || renderedPreviewCount.value <= 0) {
+    return -1
+  }
+  return Math.max(0, renderedPreviewCount.value - PREVIEW_PREFETCH_OFFSET)
+})
 
 function isStaleGeneration(token: number): boolean {
   return token !== previewGenerationToken
@@ -46,6 +63,139 @@ function scheduleGeneratePreviews(withDebounce = true) {
   }, PREVIEW_DEBOUNCE_MS)
 }
 
+function findScrollableParent(el: HTMLElement): HTMLElement | null {
+  let current: HTMLElement | null = el.parentElement
+  while (current) {
+    const style = window.getComputedStyle(current)
+    const overflowY = style.overflowY
+    if ((overflowY === 'auto' || overflowY === 'scroll') && current.scrollHeight > current.clientHeight) {
+      return current
+    }
+    current = current.parentElement
+  }
+  return null
+}
+
+function disconnectPreviewLazyLoadObserver() {
+  if (!previewLazyLoadObserver) {
+    return
+  }
+  previewLazyLoadObserver.disconnect()
+  previewLazyLoadObserver = null
+}
+
+function loadNextPreviewBatch() {
+  if (!hasMorePreviewItems.value) {
+    return
+  }
+  renderedPreviewCount.value = Math.min(
+    renderedPreviewCount.value + PREVIEW_BATCH_SIZE,
+    previewItems.value.length,
+  )
+}
+
+function bindPreviewLazyLoadObserver() {
+  disconnectPreviewLazyLoadObserver()
+
+  if (!hasMorePreviewItems.value || !previewTriggerItemEl.value) {
+    return
+  }
+
+  const root = findScrollableParent(previewTriggerItemEl.value)
+  previewLazyLoadObserver = new IntersectionObserver(
+    (entries) => {
+      const isVisible = entries.some(entry => entry.isIntersecting)
+      if (isVisible) {
+        loadNextPreviewBatch()
+      }
+    },
+    {
+      root,
+      threshold: 0.01,
+    },
+  )
+
+  previewLazyLoadObserver.observe(previewTriggerItemEl.value)
+}
+
+function setPreviewItemRef(el: unknown, index: number) {
+  if (index !== previewTriggerIndex.value) {
+    return
+  }
+  previewTriggerItemEl.value = el instanceof HTMLElement ? el : null
+}
+
+function getPreviewGeometryCacheKey(fontInfo: FontInfo): string {
+  return [
+    fontInfo.id,
+    fontInfo.path,
+    inputText.value,
+    fontSize.value,
+  ].join('::')
+}
+
+function readPreviewGeometryFromCache(key: string) {
+  const cached = previewGeometryCache.get(key)
+  if (!cached) {
+    return null
+  }
+
+  // LRU: 读取后刷新顺序
+  previewGeometryCache.delete(key)
+  previewGeometryCache.set(key, cached)
+  return cached
+}
+
+function writePreviewGeometryToCache(
+  key: string,
+  geometry: Omit<SvgGenerateResult, 'svg'> & { svgTemplate: string },
+) {
+  if (previewGeometryCache.has(key)) {
+    previewGeometryCache.delete(key)
+  }
+  previewGeometryCache.set(key, geometry)
+
+  while (previewGeometryCache.size > PREVIEW_GEOMETRY_CACHE_LIMIT) {
+    const oldestKey = previewGeometryCache.keys().next().value
+    if (oldestKey === undefined) {
+      break
+    }
+    previewGeometryCache.delete(oldestKey)
+  }
+}
+
+async function generateSvgWithPreviewCache(fontInfo: FontInfo): Promise<SvgGenerateResult | null> {
+  if (!fontInfo.font) {
+    return null
+  }
+
+  const cacheKey = getPreviewGeometryCacheKey(fontInfo)
+  let geometry = readPreviewGeometryFromCache(cacheKey)
+  if (!geometry) {
+    const baseResult = await generateSvg({
+      text: inputText.value,
+      font: fontInfo.font,
+      fontSize: fontSize.value,
+      fillColor: PREVIEW_COLOR_TOKEN,
+    })
+
+    geometry = {
+      width: baseResult.width,
+      height: baseResult.height,
+      fontName: baseResult.fontName,
+      svgTemplate: baseResult.svg,
+    }
+    writePreviewGeometryToCache(cacheKey, geometry)
+  }
+
+  return {
+    width: geometry.width,
+    height: geometry.height,
+    fontName: geometry.fontName,
+    svg: geometry.svgTemplate.split(PREVIEW_COLOR_TOKEN).join(fillColor.value),
+  }
+}
+
 watch(
   [previewFonts, inputText, fontSize, fillColor],
   () => {
@@ -55,11 +205,30 @@ watch(
   { immediate: true }
 )
 
+watch(
+  previewItems,
+  () => {
+    renderedPreviewCount.value = Math.min(PREVIEW_BATCH_SIZE, previewItems.value.length)
+  },
+  { immediate: true },
+)
+
+watch(
+  [previewTriggerIndex, hasMorePreviewItems],
+  async () => {
+    previewTriggerItemEl.value = null
+    await nextTick()
+    bindPreviewLazyLoadObserver()
+  },
+  { immediate: true },
+)
+
 onBeforeUnmount(() => {
   if (previewGenerateTimer !== null) {
     clearTimeout(previewGenerateTimer)
     previewGenerateTimer = null
   }
+  disconnectPreviewLazyLoadObserver()
   previewGenerationToken += 1
 })
 
@@ -122,12 +291,10 @@ async function generatePreviews() {
         }
 
         try {
-          const svgResult = await generateSvg({
-            text: inputText.value,
-            font: fontInfo.font,
-            fontSize: fontSize.value,
-            fillColor: fillColor.value,
-          })
+          const svgResult = await generateSvgWithPreviewCache(fontInfo)
+          if (!svgResult) {
+            continue
+          }
 
           if (isStaleGeneration(generationToken)) {
             return
@@ -197,8 +364,9 @@ defineExpose({
 
     <div v-else class="flex flex-col gap-2">
       <div
-        v-for="item in previewItems"
+        v-for="(item, index) in visiblePreviewItems"
         :key="item.fontInfo.id"
+        :ref="(el) => setPreviewItemRef(el, index)"
         class="flex flex-col gap-2"
       >
         <div class="flex items-center gap-[8px] border-b border-[#c9cdd4] pb-[8px] pr-[8px]">
@@ -226,6 +394,10 @@ defineExpose({
           <div v-html="item.svgResult.svg" class="svg-preview-container"></div>
         </div>
       </div>
+
+      <div v-if="hasMorePreviewItems" class="text-xs text-[#86909c] text-center py-2">
+        继续下滑加载更多（{{ visiblePreviewItems.length }}/{{ previewItems.length }}）
+      </div>
     </div>
   </div>
 </template>