feat: Slim dictionary (#2583)

Co-authored-by: Ryan Hitchman <hitchmanr@gmail.com>
Co-authored-by: Kurtis Grant <kurtis.b.grant@gmail.com>
Co-authored-by: kemonine <kemonine@kemonine.info>
Co-authored-by: DustinHu <hu.dustin@gmail.com>
Co-authored-by: Justin Mitchell <justin@jmitch.com>

src/activities/reader/DictionaryDefinitionActivity.cpp

@@ -0,0 +1,237 @@
+#include "DictionaryDefinitionActivity.h"
+
+#include <FontCacheManager.h>
+#include <GfxRenderer.h>
+#include <I18n.h>
+
+#include <algorithm>
+#include <cstdint>
+#include <cstdio>
+
+#include "CrossPointSettings.h"
+#include "components/UITheme.h"
+#include "fontIds.h"
+#include "util/HtmlToPlainText.h"
+
+namespace {
+
+// Longest measurable/drawable span. Wrapped lines stay under the screen width
+// (far below this); only pathological unbreakable tokens are split at this cap.
+constexpr size_t MAX_LINE_BYTES = 191;
+
+// Body text left/right inset, matching the reader's default feel.
+constexpr int SIDE_PADDING = 20;
+
+}  // namespace
+
+void DictionaryDefinitionActivity::onEnter() {
+  Activity::onEnter();
+  // Normalize StarDict multi-type separators so the wrap loop and the
+  // C-string font APIs below both see the whole definition.
+  std::replace(definition.begin(), definition.end(), '\0', '\n');
+  definition = htmlToPlainText(definition);
+  wrapText();
+  requestUpdate();
+}
+
+int DictionaryDefinitionActivity::measureSpan(const int fontId, const char* text, size_t len) const {
+  char buf[MAX_LINE_BYTES + 1];
+  len = std::min(len, MAX_LINE_BYTES);
+  memcpy(buf, text, len);
+  buf[len] = '\0';
+  return renderer.getTextAdvanceX(fontId, buf, EpdFontFamily::REGULAR);
+}
+
+// Greedy word-wrap of `definition` into byte spans. '\n' breaks lines (blank
+// lines survive as paragraph spacing; NULs from multi-type StarDict entries
+// were normalized to newlines in onEnter); '\r' is dropped by treating it as
+// a space at a token edge.
+void DictionaryDefinitionActivity::wrapText() {
+  lines.clear();
+  lines.reserve(definition.size() / 32 + 8);
+
+  const int fontId = SETTINGS.getReaderFontId();
+  // SD-card fonts: merge every definition codepoint into the persistent
+  // advance table up front. Otherwise each unseen codepoint measured below
+  // falls back to an on-demand glyph load from SD (8-slot overflow ring).
+  renderer.ensureSdCardFontReady(fontId, definition.c_str(), 0x01 /* REGULAR */);
+
+  const auto& metrics = UITheme::getInstance().getMetrics();
+  const auto orientation = renderer.getOrientation();
+  const bool isLandscape = orientation == GfxRenderer::Orientation::LandscapeClockwise ||
+                           orientation == GfxRenderer::Orientation::LandscapeCounterClockwise;
+  const bool isInverted = orientation == GfxRenderer::Orientation::PortraitInverted;
+  const int hintGutterWidth = isLandscape ? metrics.sideButtonHintsWidth : 0;
+  const int maxWidth = renderer.getScreenWidth() - hintGutterWidth - 2 * SIDE_PADDING;
+  const int spaceWidth = renderer.getSpaceWidth(fontId, EpdFontFamily::REGULAR);
+
+  const int lineHeight = renderer.getLineHeight(fontId);
+  const int topArea = (isInverted ? metrics.buttonHintsHeight : 0) + metrics.topPadding + metrics.headerHeight;
+  const int bottomArea = metrics.buttonHintsHeight + metrics.verticalSpacing;
+  linesPerPage = std::max(1, (renderer.getScreenHeight() - topArea - bottomArea) / lineHeight);
+
+  const char* text = definition.c_str();
+  const uint32_t n = static_cast<uint32_t>(definition.size());
+  uint32_t lineStart = 0;
+  uint32_t lineEnd = 0;  // one past the last token byte on the current line
+  int lineWidth = 0;
+
+  const auto flushLine = [&](uint32_t nextStart) {
+    lines.push_back({lineStart, static_cast<uint16_t>(lineEnd - lineStart)});
+    lineStart = nextStart;
+    lineEnd = nextStart;
+    lineWidth = 0;
+  };
+
+  uint32_t i = 0;
+  while (i < n) {
+    const char c = text[i];
+    if (c == '\n' || c == '\0') {
+      flushLine(i + 1);
+      i++;
+      continue;
+    }
+    if (c == ' ' || c == '\t' || c == '\r') {
+      i++;
+      continue;
+    }
+
+    // Token: run of non-whitespace bytes, capped at the measure buffer.
+    const uint32_t tokenStart = i;
+    while (i < n && text[i] != ' ' && text[i] != '\t' && text[i] != '\r' && text[i] != '\n' && text[i] != '\0' &&
+           i - tokenStart < MAX_LINE_BYTES) {
+      i++;
+    }
+    // If the byte cap cut the token mid-UTF-8-sequence, back off to the last
+    // complete codepoint so measure/draw never see a partial sequence. A
+    // natural stop lands on whitespace or the terminating NUL, never on a
+    // continuation byte, so this is a no-op there.
+    while (i - tokenStart > 1 && (text[i] & 0xC0) == 0x80) i--;
+    const uint32_t tokenLen = i - tokenStart;
+    const int tokenWidth = measureSpan(fontId, text + tokenStart, tokenLen);
+
+    if (lineEnd == lineStart) {
+      lineStart = tokenStart;
+      lineEnd = tokenStart + tokenLen;
+      lineWidth = tokenWidth;
+    } else if (lineWidth + spaceWidth + tokenWidth <= maxWidth &&
+               tokenStart + tokenLen - lineStart <= UINT16_MAX) {  // span len must fit Line::len
+      lineEnd = tokenStart + tokenLen;
+      lineWidth += spaceWidth + tokenWidth;
+    } else {
+      flushLine(tokenStart);
+      lineEnd = tokenStart + tokenLen;
+      lineWidth = tokenWidth;
+    }
+
+    // An unbreakable token wider than the screen is now alone on the line
+    // (any previous content was flushed above): split it at the widest
+    // fitting UTF-8 boundary and carry the remainder forward.
+    while (lineWidth > maxWidth && lineEnd - lineStart > 1) {
+      const uint32_t len = lineEnd - lineStart;
+      uint32_t lastFit = 0;
+      for (uint32_t f = 1; f <= len; f++) {
+        if (f == len || (text[lineStart + f] & 0xC0) != 0x80) {  // codepoint boundary
+          if (measureSpan(fontId, text + lineStart, f) > maxWidth) break;
+          lastFit = f;
+        }
+      }
+      if (lastFit == 0) {
+        // Even a single over-wide glyph must make progress; consume its whole
+        // UTF-8 sequence rather than splitting it into invalid fragments.
+        lastFit = 1;
+        while (lastFit < len && (text[lineStart + lastFit] & 0xC0) == 0x80) lastFit++;
+      }
+      const uint32_t rest = lineStart + lastFit;
+      lineEnd = rest;
+      flushLine(rest);
+      lineEnd = rest + (len - lastFit);
+      lineWidth = measureSpan(fontId, text + lineStart, lineEnd - lineStart);
+    }
+  }
+  if (lineEnd > lineStart) flushLine(n);
+
+  // Trim trailing blank lines so the last page is not empty padding.
+  while (!lines.empty() && lines.back().len == 0) lines.pop_back();
+
+  totalPages = std::max(1, (static_cast<int>(lines.size()) + linesPerPage - 1) / linesPerPage);
+  currentPage = 0;
+}
+
+void DictionaryDefinitionActivity::loop() {
+  if (mappedInput.wasReleased(MappedInputManager::Button::Back)) {
+    finish();
+    return;
+  }
+
+  buttonNavigator.onNext([this] {
+    if (currentPage + 1 < totalPages) {
+      currentPage++;
+      requestUpdate();
+    }
+  });
+
+  buttonNavigator.onPrevious([this] {
+    if (currentPage > 0) {
+      currentPage--;
+      requestUpdate();
+    }
+  });
+}
+
+// Draws the current page's line spans (copied into a stack buffer for NUL
+// termination). Called twice per render: once in font-cache scan mode, once
+// for the real paint.
+void DictionaryDefinitionActivity::drawBody(const int fontId, const int x, const int startY) const {
+  const int lineHeight = renderer.getLineHeight(fontId);
+  char buf[MAX_LINE_BYTES + 1];
+  const int firstLine = currentPage * linesPerPage;
+  const int lastLine = std::min(firstLine + linesPerPage, static_cast<int>(lines.size()));
+  for (int i = firstLine; i < lastLine; i++) {
+    if (lines[i].len == 0) continue;
+    const size_t len = std::min(static_cast<size_t>(lines[i].len), MAX_LINE_BYTES);
+    memcpy(buf, definition.c_str() + lines[i].start, len);
+    buf[len] = '\0';
+    renderer.drawText(fontId, x, startY + (i - firstLine) * lineHeight, buf);
+  }
+}
+
+void DictionaryDefinitionActivity::render(RenderLock&&) {
+  renderer.clearScreen();
+
+  const auto& metrics = UITheme::getInstance().getMetrics();
+  const auto orientation = renderer.getOrientation();
+  const bool isLandscapeCw = orientation == GfxRenderer::Orientation::LandscapeClockwise;
+  const bool isLandscapeCcw = orientation == GfxRenderer::Orientation::LandscapeCounterClockwise;
+  const bool isInverted = orientation == GfxRenderer::Orientation::PortraitInverted;
+  const int hintGutterWidth = (isLandscapeCw || isLandscapeCcw) ? metrics.sideButtonHintsWidth : 0;
+  const int contentX = isLandscapeCw ? hintGutterWidth : 0;
+  const int contentWidth = renderer.getScreenWidth() - hintGutterWidth;
+  const int contentY = isInverted ? metrics.buttonHintsHeight : 0;
+
+  // Header: matched headword left, page counter right.
+  const int headerY = contentY + metrics.topPadding + 10;
+  renderer.drawText(UI_12_FONT_ID, contentX + SIDE_PADDING, headerY, headword.c_str(), true, EpdFontFamily::BOLD);
+  if (totalPages > 1) {
+    char counter[16];
+    snprintf(counter, sizeof(counter), "%d/%d", currentPage + 1, totalPages);
+    const int counterWidth = renderer.getTextWidth(UI_10_FONT_ID, counter);
+    renderer.drawText(UI_10_FONT_ID, contentX + contentWidth - SIDE_PADDING - counterWidth, headerY, counter);
+  }
+
+  // Body: two-pass draw inside a prewarm scope (same pattern as the reader's
+  // renderContents) so SD-card font glyphs load from SD in one batch instead
+  // of one on-demand overflow read per character on every page turn.
+  const int fontId = SETTINGS.getReaderFontId();
+  const int bodyStartY = contentY + metrics.topPadding + metrics.headerHeight;
+  auto* fcm = renderer.getFontCacheManager();
+  auto scope = fcm->createPrewarmScope();
+  drawBody(fontId, contentX + SIDE_PADDING, bodyStartY);  // scan pass: records codepoints only
+  scope.endScanAndPrewarm();
+  drawBody(fontId, contentX + SIDE_PADDING, bodyStartY);
+
+  const auto labels =
+      mappedInput.mapLabels(tr(STR_BACK), "", (currentPage > 0 ? "<" : ""), (currentPage + 1 < totalPages ? ">" : ""));
+  GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+  renderer.displayBuffer();
+}

src/activities/reader/DictionaryDefinitionActivity.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+#include "activities/Activity.h"
+#include "util/ButtonNavigator.h"
+
+// Paged plain-text viewer for one dictionary definition. The definition is
+// word-wrapped once on entry; each page renders spans of the original string,
+// so no per-line copies are held.
+class DictionaryDefinitionActivity final : public Activity {
+ public:
+  explicit DictionaryDefinitionActivity(GfxRenderer& renderer, MappedInputManager& mappedInput, std::string headword,
+                                        std::string definition)
+      : Activity("DictionaryDefinition", renderer, mappedInput),
+        headword(std::move(headword)),
+        definition(std::move(definition)) {}
+
+  void onEnter() override;
+  void loop() override;
+  void render(RenderLock&&) override;
+
+ private:
+  // One wrapped display line: a byte span of `definition`. Wrapping keeps
+  // lines under the screen width, so uint16_t length is ample.
+  struct Line {
+    uint32_t start;
+    uint16_t len;
+  };
+
+  void wrapText();
+  int measureSpan(int fontId, const char* text, size_t len) const;
+  void drawBody(int fontId, int x, int startY) const;
+
+  const std::string headword;
+  // Not const: onEnter() normalizes embedded NULs (StarDict multi-type
+  // separators) to newlines so C-string APIs see the whole text.
+  std::string definition;
+  std::vector<Line> lines;
+  int currentPage = 0;
+  int totalPages = 1;
+  int linesPerPage = 1;
+  ButtonNavigator buttonNavigator;
+};

src/activities/reader/DictionaryWordSelectActivity.cpp

@@ -0,0 +1,301 @@
+#include "DictionaryWordSelectActivity.h"
+
+#include <FontCacheManager.h>
+#include <GfxRenderer.h>
+#include <Memory.h>
+#include <freertos/FreeRTOS.h>
+#include <freertos/task.h>
+
+#include <cctype>
+#include <climits>
+#include <cstdlib>
+
+#include "CrossPointSettings.h"
+#include "DictionaryDefinitionActivity.h"
+#include "components/UITheme.h"
+
+namespace {
+
+constexpr unsigned long POPUP_DURATION_MS = 1500;
+
+// A token is selectable when it has an ASCII alphanumeric or a non-ASCII
+// codepoint outside U+2000-U+206F (dashes, bullets and other General
+// Punctuation that appear as standalone tokens are not words).
+bool isSelectableToken(const char* text) {
+  for (const uint8_t* p = reinterpret_cast<const uint8_t*>(text); *p != 0; p++) {
+    if (*p < 0x80) {
+      if (std::isalnum(*p)) return true;
+    } else if (*p == 0xE2 && (p[1] == 0x80 || p[1] == 0x81)) {
+      if (p[2] == 0) break;  // truncated sequence: skipping would step past the NUL
+      p += 2;                // skip the 3-byte General Punctuation codepoint
+    } else {
+      return true;
+    }
+  }
+  return false;
+}
+
+void indexBuildYield(void*) { vTaskDelay(1); }
+
+}  // namespace
+
+void DictionaryWordSelectActivity::onEnter() {
+  Activity::onEnter();
+  fontId = SETTINGS.getReaderFontId();
+  lineHeight = renderer.getLineHeight(fontId);
+  // No null check: a failed allocation just disables the differential
+  // fast path (drawHighlightWithSnapshot skips the read), keeping the
+  // full-repaint path as the fallback.
+  snapshot = makeUniqueNoThrow<uint8_t[]>(SNAPSHOT_CAPACITY);
+  extractWords();
+  // Start on the middle row's word nearest mid-screen instead of top-left:
+  // any word on the page is then at most half a page of moves away.
+  if (!words.empty()) {
+    const int initial = closestInRow(rowCount / 2, renderer.getScreenWidth() / 2);
+    if (initial >= 0) selected = initial;
+  }
+  requestUpdate();
+}
+
+void DictionaryWordSelectActivity::extractWords() {
+  words.clear();
+  words.reserve(128);
+  rowCount = 0;
+
+  // Single walk: collect the selectable words while accumulating their text
+  // and styles (~2KB transient string, freed on return). Widths are measured
+  // afterwards: merging the page's codepoints into the SD font's persistent
+  // advance table first keeps getTextAdvanceX on the in-RAM path instead of
+  // loading glyphs from SD one overflow slot at a time.
+  std::string pageText;
+  pageText.reserve(2048);
+  uint8_t styleMask = 0;
+
+  for (const auto& element : page->elements) {
+    if (element->getTag() != TAG_PageLine) continue;
+    const auto* line = static_cast<const PageLine*>(element.get());
+    const auto& block = line->getBlock();
+    if (!block || !block->valid()) continue;
+
+    bool rowHasWords = false;
+    for (uint16_t i = 0; i < block->wordCount(); i++) {
+      const char* text = block->wordText(i);
+      if (!isSelectableToken(text)) continue;
+
+      WordBox box;
+      box.x = static_cast<int16_t>(line->xPos + block->wordXpos(i) + marginLeft);
+      box.y = static_cast<int16_t>(line->yPos + marginTop);
+      box.style = block->wordStyle(i);
+      box.width = 0;  // measured below, once the advance table is ready
+      box.row = rowCount;
+      box.text = text;
+      words.push_back(box);
+      rowHasWords = true;
+
+      pageText.append(text);
+      pageText.push_back(' ');
+      styleMask |= static_cast<uint8_t>(1u << (static_cast<uint8_t>(box.style) & 0x03));
+    }
+    if (rowHasWords) rowCount++;
+  }
+
+  if (styleMask == 0) styleMask = 0x01;  // REGULAR
+  renderer.ensureSdCardFontReady(fontId, pageText.c_str(), styleMask);
+  for (auto& word : words) {
+    word.width = static_cast<int16_t>(renderer.getTextAdvanceX(fontId, word.text, word.style));
+  }
+}
+
+// Index of the word in `row` whose horizontal center is closest to centerX;
+// -1 when the row has no words.
+int DictionaryWordSelectActivity::closestInRow(const uint16_t row, const int centerX) const {
+  int best = -1;
+  int bestDistance = INT_MAX;
+  for (int i = 0; i < static_cast<int>(words.size()); i++) {
+    if (words[i].row != row) continue;
+    const int distance = std::abs(words[i].x + words[i].width / 2 - centerX);
+    if (distance < bestDistance) {
+      bestDistance = distance;
+      best = i;
+    }
+  }
+  return best;
+}
+
+void DictionaryWordSelectActivity::moveVertical(const int direction) {
+  const WordBox& current = words[selected];
+  const int targetRow = static_cast<int>(current.row) + direction;
+  if (targetRow < 0 || targetRow >= static_cast<int>(rowCount)) return;
+
+  const int best = closestInRow(static_cast<uint16_t>(targetRow), current.x + current.width / 2);
+  if (best >= 0 && best != selected) {
+    selected = best;
+    requestUpdate();
+  }
+}
+
+void DictionaryWordSelectActivity::performLookup() {
+  popup = Popup::Busy;
+  if (!dictOpenAttempted) {
+    dictOpenAttempted = true;
+    dictOpenOk = dict.open(SETTINGS.dictionaryName);
+  }
+  const bool indexing = dictOpenOk && dict.needsIndex();
+  popupMsg = indexing ? StrId::STR_DICT_INDEXING : StrId::STR_DICT_LOOKING_UP;
+  requestUpdateAndWait();  // paint the page + busy popup before blocking on SD
+
+  bool ok = dictOpenOk;
+  if (ok && indexing) ok = dict.buildIndex(&indexBuildYield);
+
+  std::string definition;
+  std::string headword;
+  const bool found = ok && dict.lookup(words[selected].text, definition, headword);
+
+  if (found) {
+    popup = Popup::None;
+    startActivityForResult(std::make_unique<DictionaryDefinitionActivity>(renderer, mappedInput, std::move(headword),
+                                                                          std::move(definition)),
+                           [this](const ActivityResult&) { requestUpdate(); });
+    return;
+  }
+  popup = ok ? Popup::NotFound : Popup::Error;
+  popupMsg = ok ? StrId::STR_DICT_NOT_FOUND : StrId::STR_DICT_ERROR;
+  popupTime = millis();
+  requestUpdate();
+}
+
+void DictionaryWordSelectActivity::loop() {
+  if (popup == Popup::NotFound || popup == Popup::Error) {
+    if (millis() - popupTime >= POPUP_DURATION_MS) {
+      popup = Popup::None;
+      requestUpdate();
+    }
+    return;
+  }
+
+  if (mappedInput.wasPressed(MappedInputManager::Button::Confirm)) confirmPressSeen = true;
+
+  if (mappedInput.wasReleased(MappedInputManager::Button::Back)) {
+    finish();
+    return;
+  }
+  if (mappedInput.wasReleased(MappedInputManager::Button::Confirm) && confirmPressSeen && !words.empty()) {
+    performLookup();
+    return;
+  }
+
+  if (words.empty()) return;
+  if (mappedInput.wasPressed(MappedInputManager::Button::Left) && selected > 0) {
+    selected--;
+    requestUpdate();
+  } else if (mappedInput.wasPressed(MappedInputManager::Button::Right) &&
+             selected + 1 < static_cast<int>(words.size())) {
+    selected++;
+    requestUpdate();
+  } else if (mappedInput.wasPressed(MappedInputManager::Button::Up)) {
+    moveVertical(-1);
+  } else if (mappedInput.wasPressed(MappedInputManager::Button::Down)) {
+    moveVertical(1);
+  }
+}
+
+// Saves the pixels under words[selected]'s highlight box, then draws the
+// highlight over them. Returns false when the pixels could not be saved
+// (no buffer / oversize box) — the highlight is drawn regardless, but the
+// next cursor move must do a full repaint.
+bool DictionaryWordSelectActivity::drawHighlightWithSnapshot() {
+  const WordBox& word = words[selected];
+  int hx = word.x - 2;
+  int hy = word.y - 2;
+  int hw = word.width + 4;
+  int hh = lineHeight + 4;
+  // Clamp to the panel so save, draw and restore all use the same box.
+  if (hx < 0) {
+    hw += hx;
+    hx = 0;
+  }
+  if (hy < 0) {
+    hh += hy;
+    hy = 0;
+  }
+
+  bool saved = false;
+  if (snapshot && hw > 0 && hh > 0) {
+    saved = renderer.readFramebufferRegion(hx, hy, hw, hh, snapshot.get(), SNAPSHOT_CAPACITY) > 0;
+  }
+  snapshotX = static_cast<int16_t>(hx);
+  snapshotY = static_cast<int16_t>(hy);
+  snapshotW = static_cast<int16_t>(hw);
+  snapshotH = static_cast<int16_t>(hh);
+  snapshotIdx = saved ? selected : -1;
+
+  renderer.fillRect(hx, hy, hw, hh, true);
+  renderer.drawText(fontId, word.x, word.y, word.text, false, word.style);
+  return saved;
+}
+
+// Front-button bar (Back/Confirm/Left/Right). Drawn last on every repaint
+// path, including the differential highlight-only path, so it always ends
+// up as the top layer even when a highlighted word's box falls under a
+// hint's screen area. No side-button hints: Up/Down row jump has no spare
+// screen area on this page (it reuses the reader's full-bleed layout), and
+// a hint box there would hide text instead of sitting in a reserved gutter.
+void DictionaryWordSelectActivity::drawHints() const {
+  // No selectable word on this page: Confirm/Left/Right are all no-ops
+  // (guarded by words.empty() in loop()/performLookup), so only Back does
+  // anything and only Back is hinted.
+  if (words.empty()) {
+    const auto labels = mappedInput.mapLabels(tr(STR_BACK), "", "", "");
+    GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+    return;
+  }
+  const auto labels = mappedInput.mapLabels(tr(STR_BACK), tr(STR_LOOKUP), tr(STR_DIR_LEFT), tr(STR_DIR_RIGHT));
+  GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
+}
+
+void DictionaryWordSelectActivity::render(RenderLock&&) {
+  // Differential fast path: only the highlight moved and the framebuffer
+  // still holds a clean page (no popup or sub-activity since the last full
+  // repaint). Restore the pixels under the old highlight, draw the new one,
+  // and push — skipping the two-pass page render entirely.
+  if (popup == Popup::None && snapshotIdx >= 0 && !words.empty() && selected != snapshotIdx) {
+    renderer.writeFramebufferRegion(snapshotX, snapshotY, snapshotW, snapshotH, snapshot.get());
+    // The full path's PrewarmScope cleared the glyph cache on exit; batch-load
+    // just the highlighted word's glyphs before drawing them white-on-black.
+    renderer.getFontCacheManager()->prewarmCache(
+        fontId, words[selected].text, static_cast<uint8_t>(1u << (static_cast<uint8_t>(words[selected].style) & 0x03)));
+    if (drawHighlightWithSnapshot()) {
+      drawHints();
+      renderer.displayBuffer(HalDisplay::FAST_REFRESH);
+      return;
+    }
+    // Snapshot failed (oversize box) — fall through to a full repaint.
+  }
+
+  renderer.clearScreen();
+
+  // Same prewarm-scan-then-render pass the reader uses, so SD-card fonts hit
+  // the in-RAM glyph cache during the real draw.
+  auto* fcm = renderer.getFontCacheManager();
+  auto scope = fcm->createPrewarmScope();
+  page->render(renderer, fontId, marginLeft, marginTop);
+  scope.endScanAndPrewarm();
+  page->render(renderer, fontId, marginLeft, marginTop);
+
+  if (!words.empty()) {
+    drawHighlightWithSnapshot();
+  }
+
+  drawHints();
+
+  if (popup != Popup::None) {
+    // The popup overdraws the page, so the snapshot no longer matches the
+    // framebuffer — force the next render onto the full-repaint path.
+    snapshotIdx = -1;
+    // drawPopup overlays the framebuffer and refreshes the display itself.
+    // I18N.get directly: tr() only accepts literal key names.
+    GUI.drawPopup(renderer, I18N.get(popupMsg));
+    return;
+  }
+  renderer.displayBuffer(HalDisplay::FAST_REFRESH);
+}

src/activities/reader/DictionaryWordSelectActivity.h

@@ -0,0 +1,84 @@
+#pragma once
+
+#include <Epub/Page.h>
+#include <I18n.h>
+
+#include <memory>
+#include <vector>
+
+#include "activities/Activity.h"
+#include "util/Dictionary.h"
+
+// Button-driven word selection over the current reader page: Left/Right step
+// through words in reading order, Up/Down jump rows, Confirm looks the word up
+// and opens DictionaryDefinitionActivity, Back returns to the reader.
+class DictionaryWordSelectActivity final : public Activity {
+ public:
+  explicit DictionaryWordSelectActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                                        std::unique_ptr<Page> page, int marginLeft, int marginTop)
+      : Activity("DictionaryWordSelect", renderer, mappedInput),
+        page(std::move(page)),
+        marginLeft(marginLeft),
+        marginTop(marginTop) {}
+
+  void onEnter() override;
+  void loop() override;
+  void render(RenderLock&&) override;
+
+ private:
+  // Screen box of one selectable word. `text` points into the owned Page's
+  // TextBlock arena (NUL-terminated), valid for this activity's lifetime.
+  struct WordBox {
+    int16_t x;
+    int16_t y;
+    int16_t width;
+    uint16_t row;
+    const char* text;
+    EpdFontFamily::Style style;
+  };
+
+  enum class Popup : uint8_t { None, Busy, NotFound, Error };
+
+  void extractWords();
+  int closestInRow(uint16_t row, int centerX) const;
+  void moveVertical(int direction);
+  void performLookup();
+  bool drawHighlightWithSnapshot();
+  void drawHints() const;
+
+  std::unique_ptr<Page> page;
+  const int marginLeft;
+  const int marginTop;
+  int fontId = 0;
+  int lineHeight = 0;
+
+  std::vector<WordBox> words;
+  int selected = 0;
+  uint16_t rowCount = 0;
+
+  Dictionary dict;
+  bool dictOpenAttempted = false;
+  bool dictOpenOk = false;
+
+  Popup popup = Popup::None;
+  StrId popupMsg = StrId::STR_DICT_NOT_FOUND;
+  unsigned long popupTime = 0;
+
+  // Differential highlight repaint: the pixels under the current highlight
+  // box, so a cursor move restores them and repaints only the two affected
+  // boxes instead of re-running the full two-pass page render (which also
+  // reloads every SD-font glyph on the page). snapshotIdx is the word whose
+  // under-pixels are saved; -1 means the framebuffer no longer holds a clean
+  // page (popup drawn, sub-activity shown) and the next render must be full.
+  static constexpr size_t SNAPSHOT_CAPACITY = 4096;
+  std::unique_ptr<uint8_t[]> snapshot;
+  int16_t snapshotX = 0;
+  int16_t snapshotY = 0;
+  int16_t snapshotW = 0;
+  int16_t snapshotH = 0;
+  int snapshotIdx = -1;
+
+  // The activity is entered while Confirm is still held (long-press trigger):
+  // ignore the stale release until a fresh press is seen.
+  bool confirmPressSeen = false;
+};

src/activities/reader/EpubReaderActivity.cpp

@@ -20,6 +20,7 @@
 #include "BookmarkEntry.h"
 #include "CrossPointSettings.h"
 #include "CrossPointState.h"
+#include "DictionaryWordSelectActivity.h"
 #include "EpubReaderBookmarksActivity.h"
 #include "EpubReaderChapterSelectionActivity.h"
 #include "EpubReaderFootnotesActivity.h"
@@ -257,6 +258,29 @@ void EpubReaderActivity::openReaderMenu() {
                          });
 }
 
+void EpubReaderActivity::openDictionaryWordSelect() {
+  if (SETTINGS.dictionaryName[0] == '\0') {
+    showDictionaryMessage = true;
+    dictionaryMessageTime = millis();
+    requestUpdate();
+    return;
+  }
+  if (!section) return;
+  auto page = section->loadPage(section->currentPage);
+  if (!page) return;
+
+  // Word geometry must match render(): viewable-area margins plus screen margin.
+  int orientedMarginTop, orientedMarginRight, orientedMarginBottom, orientedMarginLeft;
+  renderer.getOrientedViewableTRBL(&orientedMarginTop, &orientedMarginRight, &orientedMarginBottom,
+                                   &orientedMarginLeft);
+  orientedMarginTop += SETTINGS.screenMargin;
+  orientedMarginLeft += SETTINGS.screenMargin;
+
+  startActivityForResult(std::make_unique<DictionaryWordSelectActivity>(renderer, mappedInput, std::move(page),
+                                                                        orientedMarginLeft, orientedMarginTop),
+                         [this](const ActivityResult&) { requestUpdate(); });
+}
+
 void EpubReaderActivity::loop() {
   if (!epub) {
     // Should never happen
@@ -379,6 +403,11 @@ void EpubReaderActivity::loop() {
     requestUpdate();
   }
 
+  if (showDictionaryMessage && (millis() - dictionaryMessageTime) >= ReaderUtils::BOOKMARK_MESSAGE_DURATION_MS) {
+    showDictionaryMessage = false;
+    requestUpdate();
+  }
+
   // While the end screen suggestion menu is showing it owns Confirm/Back/navigation
   // input. Anything it doesn't handle (e.g. long-press Back to the file browser) falls
   // through to the regular handlers below; page turns are absorbed by the end-of-book
@@ -442,6 +471,14 @@ void EpubReaderActivity::loop() {
           }
         }
         break;
+      case CrossPointSettings::LP_MENU_DICTIONARY:
+        // Hold ~0.4s starts dictionary word selection on the current page.
+        if (mappedInput.getHeldTime() >= ReaderUtils::BOOKMARK_HOLD_MS && !showDictionaryMessage) {
+          ignoreNextConfirmRelease = true;  // Prevent menu open on the release that follows
+          openDictionaryWordSelect();
+          return;
+        }
+        break;
       case CrossPointSettings::LP_MENU_DISABLED:
       default:
         break;
@@ -710,6 +747,10 @@ void EpubReaderActivity::onReaderMenuConfirm(EpubReaderMenuActivity::MenuAction
           });
       break;
     }
+    case EpubReaderMenuActivity::MenuAction::DICTIONARY: {
+      openDictionaryWordSelect();
+      break;
+    }
     case EpubReaderMenuActivity::MenuAction::DISPLAY_QR: {
       if (section && section->currentPage >= 0 && section->currentPage < section->pageCount) {
         std::string fullText = section->getTextFromSectionFile();
@@ -1300,6 +1341,10 @@ void EpubReaderActivity::render(RenderLock&& lock) {
   if (showBookmarkMessage) {
     GUI.drawPopup(renderer, bookmarkRemoved ? tr(STR_BOOKMARK_REMOVED) : tr(STR_BOOKMARK_ADDED));
   }
+
+  if (showDictionaryMessage) {
+    GUI.drawPopup(renderer, tr(STR_DICT_NO_DICT_SET));
+  }
 }
 
 bool EpubReaderActivity::applyDeferredReposition() {

src/activities/reader/EpubReaderActivity.h

@@ -39,6 +39,9 @@ class EpubReaderActivity final : public Activity {
   bool skipNextButtonCheck = false;  // Skip button processing for one frame after subactivity exit
   bool automaticPageTurnActive = false;
   bool showBookmarkMessage = false;
+  // "No dictionary set" popup, shown when a lookup is triggered without a configured dictionary.
+  bool showDictionaryMessage = false;
+  unsigned long dictionaryMessageTime = 0UL;
   bool ignoreNextConfirmRelease = false;
   bool currentPageBookmarked = false;
   bool bookmarkRemoved = false;  // true when last toggle removed (controls popup text)
@@ -119,6 +122,7 @@ class EpubReaderActivity final : public Activity {
   void onReaderMenuConfirm(EpubReaderMenuActivity::MenuAction action);
   // Opens the reader menu for the current position (short-press Confirm)
   void openReaderMenu();
+  void openDictionaryWordSelect();
   // Returns true if sync acted (launched, or surfaced a save error); false if it was a no-op
   // because no KOReader credentials are stored.
   bool launchKOReaderSync();

src/activities/reader/EpubReaderMenuActivity.cpp

@@ -22,7 +22,7 @@ EpubReaderMenuActivity::EpubReaderMenuActivity(GfxRenderer& renderer, MappedInpu
 std::vector<EpubReaderMenuActivity::MenuItem> EpubReaderMenuActivity::buildMenuItems(bool hasFootnotes,
                                                                                      bool hasBookmarks) {
   std::vector<MenuItem> items;
-  items.reserve(12);
+  items.reserve(13);
   items.push_back({MenuAction::SELECT_CHAPTER, StrId::STR_SELECT_CHAPTER});
   if (hasFootnotes) {
     items.push_back({MenuAction::FOOTNOTES, StrId::STR_FOOTNOTES});
@@ -31,6 +31,7 @@ std::vector<EpubReaderMenuActivity::MenuItem> EpubReaderMenuActivity::buildMenuI
     items.push_back({MenuAction::BOOKMARKS, StrId::STR_BOOKMARKS});
   }
   items.push_back({MenuAction::TOGGLE_BOOKMARK, StrId::STR_TOGGLE_BOOKMARK});
+  items.push_back({MenuAction::DICTIONARY, StrId::STR_LOOKUP});
   items.push_back({MenuAction::ROTATE_SCREEN, StrId::STR_ORIENTATION});
   items.push_back({MenuAction::AUTO_PAGE_TURN, StrId::STR_AUTO_TURN_PAGES_PER_MIN});
   items.push_back({MenuAction::GO_TO_PERCENT, StrId::STR_GO_TO_PERCENT});

src/activities/reader/EpubReaderMenuActivity.h

@@ -24,7 +24,8 @@ class EpubReaderMenuActivity final : public Activity {
     DISPLAY_QR,
     GO_HOME,
     SYNC,
-    DELETE_CACHE
+    DELETE_CACHE,
+    DICTIONARY
   };
 
   explicit EpubReaderMenuActivity(GfxRenderer& renderer, MappedInputManager& mappedInput, const std::string& title,

src/activities/settings/SettingsActivity.cpp

@@ -39,7 +39,12 @@ void SettingsActivity::rebuildSettingsLists() {
   // reader activity ran — otherwise the font-family picker shows stale list.
   sdFontSystem.refreshIfDirty();
 
-  for (auto& setting : getSettingsList(&sdFontSystem.registry())) {
+  // Rescan /dictionaries on every rebuild: cheap (one directory listing) and
+  // picks up dictionaries copied to the SD card since the last visit.
+  std::vector<DictionaryEntry> dictionaries;
+  DictionaryRegistry::discover(dictionaries);
+
+  for (auto& setting : getSettingsList(&sdFontSystem.registry(), &dictionaries)) {
     if (setting.category == StrId::STR_NONE_OPT) continue;
     if (setting.category == StrId::STR_CAT_DISPLAY) {
       displaySettings.push_back(setting);