feat: Seamless sleep/wake screens for displaying book pages during deep sleep (#2064)

<img width="605" height="454" alt="image"
src="https://github.com/user-attachments/assets/bfd84afe-3b58-436e-9a5d-539af3ec3d4e"
/>

Actualized "Last" sleep screen setting from previous PRs, rebranded as a
~~`Seamless Sleep`~~ `Page as Sleep Screen` option with more
improvements.


https://github.com/user-attachments/assets/59029ba6-007e-4841-abfa-f680d7e98b79

---

New option: `Page as Sleep Screen` - `Never (default)`, `After Timeout`,
`Always`

When enabled, it seamlessly sleeps on timeout or power off, making a
fast refresh for the moon icon. When waking up, we still show the last
page, instead of the boot screen, making it fully seamless.

I tried different icons such as "refresh arrow" and others, but they
looked not as nice as 3 simple dots.

With this mode, the device turns off 4 seconds faster. And has 6 seconds
less delay when turning back on. Much more responsive.

Previously, even a 10-minute timeout sometimes wasn't enough, and I'd
worry about seeing the book cover. It's now easier to use a shorter
sleep timeout: if I get distracted during a reading session but don't
want to stop, the new screen is much more inviting to come back to.

---

Did you use AI tools to help write this code? _**PARTIALLY**_.

---

Test v1.3.0 firmware.bin file
[download](https://github.com/user-attachments/files/28015193/firmware.zip)

Based on PRs #410 and #495

Closes #400, #1649

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main.cpp

@@ -30,6 +30,7 @@
 #include "activities/settings/SdFirmwareUpdateActivity.h"
 #include "components/UITheme.h"
 #include "fontIds.h"
+#include "images/LoadingIcon.h"
 #include "util/ButtonNavigator.h"
 #include "util/ScreenshotUtil.h"
 
@@ -39,6 +40,7 @@ ActivityManager activityManager(renderer, mappedInputManager);
 FontDecompressor fontDecompressor;
 SdCardFontSystem sdFontSystem;
 FontCacheManager fontCacheManager(renderer.getFontMap(), renderer.getSdCardFonts());
+static unsigned long allowSleepAt = 0;
 
 // Fonts
 EpdFont notoserif14RegularFont(&notoserif_14_regular);
@@ -207,13 +209,46 @@ void waitForPowerRelease() {
   }
 }
 
+constexpr char SLEEP_FRAME_FILE[] = "/.crosspoint/sleep_frame.bin";
+
+static void saveSleepFrameBuffer() {
+  FsFile file;
+  if (!Storage.openFileForWrite("SLP", SLEEP_FRAME_FILE, file)) return;
+  file.write(renderer.getFrameBuffer(), renderer.getBufferSize());
+  file.close();
+}
+
+static bool loadSleepFrameBuffer() {
+  FsFile file;
+  if (!Storage.openFileForRead("SLP", SLEEP_FRAME_FILE, file)) return false;
+  const size_t bufferSize = display.getBufferSize();
+  const size_t bytesRead = file.read(display.getFrameBuffer(), bufferSize);
+  file.close();
+  if (bytesRead != bufferSize) {
+    Storage.remove(SLEEP_FRAME_FILE);
+    return false;
+  }
+  Storage.remove(SLEEP_FRAME_FILE);
+  return true;
+}
+
 // Enter deep sleep mode
-void enterDeepSleep() {
+void enterDeepSleep(bool fromTimeout = false) {
   HalPowerManager::Lock powerLock;  // Ensure we are at normal CPU frequency for sleep preparation
   APP_STATE.lastSleepFromReader = activityManager.isReaderActivity();
+
+  const bool isSeamless = SETTINGS.seamlessSleepScreen == CrossPointSettings::SEAMLESS_SLEEP_SCREEN::SEAMLESS_ALWAYS ||
+                          (fromTimeout && SETTINGS.seamlessSleepScreen ==
+                                              CrossPointSettings::SEAMLESS_SLEEP_SCREEN::SEAMLESS_AFTER_TIMEOUT);
+  APP_STATE.showBootScreen = !isSeamless;
+
   APP_STATE.saveToFile();
 
-  activityManager.goToSleep();
+  activityManager.goToSleep(fromTimeout);
+
+  if (isSeamless) {
+    saveSleepFrameBuffer();
+  }
 
   // Tear down WiFi so the modem power domain isn't held alive across deep sleep.
   // Wake from deep sleep is effectively a chip reset, so no state needs to survive.
@@ -229,8 +264,8 @@ void enterDeepSleep() {
   powerManager.startDeepSleep(gpio);
 }
 
-void setupDisplayAndFonts() {
-  display.begin();
+void setupDisplayAndFonts(bool seamless = false) {
+  display.begin(seamless);
   renderer.begin();
   activityManager.begin();
   LOG_DBG("MAIN", "Display initialized");
@@ -313,6 +348,8 @@ void setup() {
   HalSystem::checkPanic();
 
   SETTINGS.loadFromFile();
+  APP_STATE.loadFromFile();
+  RECENT_BOOKS.loadFromFile();
   I18N.setLanguage(static_cast<Language>(SETTINGS.language));
   KOREADER_STORE.loadFromFile();
   OPDS_STORE.loadFromFile();
@@ -360,17 +397,28 @@ void setup() {
   // First serial output only here to avoid timing inconsistencies for power button press duration verification
   LOG_DBG("MAIN", "Starting CrossPoint version " CROSSPOINT_VERSION);
 
-  setupDisplayAndFonts();
+  setupDisplayAndFonts(/*seamless=*/!APP_STATE.showBootScreen);
 
   // First paint after silent reboot is HALF_REFRESH (SDK forces it after begin()'s
   // panel reset); subsequent paints FAST.
   if (!isSilentReboot) {
-    activityManager.goToBoot();
+    if (APP_STATE.showBootScreen) {
+      activityManager.goToBoot();
+    } else if (loadSleepFrameBuffer()) {
+      // Seamless wake: buffer restored, replace moon icon with loading icon
+      const auto pageHeight = renderer.getScreenHeight();
+      renderer.drawImage(LoadingIcon, 0, pageHeight - LOADINGICON_HEIGHT, LOADINGICON_WIDTH, LOADINGICON_HEIGHT);
+      renderer.displayBuffer(HalDisplay::HALF_REFRESH);
+      APP_STATE.showBootScreen = true;
+      APP_STATE.saveToFile();
+    } else {
+      // Frame buffer file missing — fall back to normal boot screen
+      APP_STATE.showBootScreen = true;
+      APP_STATE.saveToFile();
+      activityManager.goToBoot();
+    }
   }
 
-  APP_STATE.loadFromFile();
-  RECENT_BOOKS.loadFromFile();
-
   if (recoveryFirmwareMode) {
     // Skip normal home/reader routing: jump straight into the SD firmware picker.
     activityManager.replaceActivity(
@@ -401,6 +449,7 @@ void setup() {
 
   // Ensure we're not still holding the power button before leaving setup
   waitForPowerRelease();
+  allowSleepAt = millis() + 2000;
 }
 
 void loop() {
@@ -471,12 +520,13 @@ void loop() {
   const unsigned long sleepTimeoutMs = SETTINGS.getSleepTimeoutMs();
   if (millis() - lastActivityTime >= sleepTimeoutMs) {
     LOG_DBG("SLP", "Auto-sleep triggered after %lu ms of inactivity", sleepTimeoutMs);
-    enterDeepSleep();
+    enterDeepSleep(true);
     // This should never be hit as `enterDeepSleep` calls esp_deep_sleep_start
     return;
   }
 
-  if (gpio.isPressed(HalGPIO::BTN_POWER) && gpio.getPowerButtonHeldTime() > SETTINGS.getPowerButtonDuration()) {
+  if (millis() >= allowSleepAt && gpio.isPressed(HalGPIO::BTN_POWER) &&
+      gpio.getPowerButtonHeldTime() > SETTINGS.getPowerButtonDuration()) {
     // If the screenshot combination is potentially being pressed, don't sleep
     if (gpio.isPressed(HalGPIO::BTN_DOWN)) {
       return;