Add touch reader controls for page navigation

Implements tap zones on touch devices for page back/forward navigation and press-and-hold actions, mirroring physical button behavior. Adds isXteinkDevice() helper to distinguish Xteink X3/X4 boards from touch devices. The sunlight fading fix setting is now exclusive to Xteink devices, while touch devices get the new touch reader controls toggle instead.

src/CrossPointSettings.h

@@ -230,6 +230,9 @@ class CrossPointSettings {
   uint8_t uiTheme = LYRA;
   // Sunlight fading compensation
   uint8_t fadingFix = 0;
+  // Touch reader controls: tap zones for page back/forward + press-and-hold,
+  // mirroring the physical buttons. Touch devices only (hidden elsewhere).
+  uint8_t touchReaderControls = 1;
   // Power button return from footnotes (1 = enabled, 0 = disabled)
   uint8_t pwrBtnFootnoteBack = 1;
   // Use book's embedded CSS styles for EPUB rendering (1 = enabled, 0 = disabled)

src/SettingsList.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <HalClock.h>
+#include <HalGPIO.h>
 #include <HalTiltSensor.h>
 #include <I18n.h>
 #include <SdCardFontRegistry.h>
@@ -252,6 +253,26 @@ inline std::vector<SettingInfo> getSettingsList(const SdCardFontRegistry* regist
         SettingInfo::Toggle(StrId::STR_CLOCK_SYNCED, &CrossPointSettings::clockHasBeenSynced, "clockHasBeenSynced",
                             StrId::STR_CUSTOMISE_STATUS_BAR),
     };
+    // The sunlight fading fix targets the Xteink X3/X4 transflective panel, so
+    // it only appears on those devices. Every other (touch) device instead gets
+    // the touch reader controls toggle (tap page back/forward + press-and-hold,
+    // mirroring the physical buttons). Keyed off the board identity
+    // (gpio.isXteinkDevice()), not gpio.hasTouch(), so the reader runtime gate
+    // and this visibility gate share one source of truth.
+    if (!gpio.isXteinkDevice()) {
+      v.erase(std::remove_if(v.begin(), v.end(),
+                             [](const SettingInfo& s) { return s.nameId == StrId::STR_SUNLIGHT_FADING_FIX; }),
+              v.end());
+      for (auto it = v.begin(); it != v.end(); ++it) {
+        if (it->nameId == StrId::STR_SIDE_BTN_LAYOUT) {
+          v.insert(it, SettingInfo::Toggle(StrId::STR_TOUCH_READER_CONTROLS,
+                                           &CrossPointSettings::touchReaderControls, "touchReaderControls",
+                                           StrId::STR_CAT_CONTROLS));
+          break;
+        }
+      }
+    }
+
     // Only show tilt page turn setting when the QMI8658 IMU is present (X3)
     if (halTiltSensor.isAvailable()) {
       // Insert after the short power button setting (end of Controls section)

src/activities/reader/EpubReaderActivity.cpp

@@ -338,7 +338,15 @@ void EpubReaderActivity::loop() {
     return;
   }
 
-  const auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
+  // Touch reader controls mirror the side page buttons (left third = back,
+  // right third = forward, press-and-hold = long-press behavior). The top-left
+  // Back corner is consumed by wasReleased(Back) earlier, so it never reaches
+  // here. No-op on Xteink / when the setting is off.
+  const auto touch = ReaderUtils::detectTouchPageTurn(renderer);
+
+  auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
+  prevTriggered = prevTriggered || touch.prev;
+  nextTriggered = nextTriggered || touch.next;
   if (!prevTriggered && !nextTriggered) {
     return;
   }
@@ -356,7 +364,8 @@ void EpubReaderActivity::loop() {
     return;
   }
 
-  const bool longPress = !fromTilt && mappedInput.getHeldTime() > ReaderUtils::SKIP_HOLD_MS;
+  const unsigned long heldMs = (touch.prev || touch.next) ? touch.heldMs : mappedInput.getHeldTime();
+  const bool longPress = !fromTilt && heldMs > ReaderUtils::SKIP_HOLD_MS;
 
   // Don't skip chapter after screenshot
   if (gpio.wasReleased(HalGPIO::BTN_POWER) && gpio.wasReleased(HalGPIO::BTN_DOWN)) {

src/activities/reader/ReaderUtils.h

@@ -2,6 +2,7 @@
 
 #include <CrossPointSettings.h>
 #include <GfxRenderer.h>
+#include <HalGPIO.h>
 #include <HalTiltSensor.h>
 #include <Logging.h>
 
@@ -61,6 +62,40 @@ inline PageTurnResult detectPageTurn(const MappedInputManager& input) {
   return {prev, next, tiltPrev || tiltNext};
 }
 
+// Touch reader controls: a tap on the left third of the (oriented) screen turns
+// back a page, the right third turns forward, mirroring the side page buttons.
+// heldMs carries the contact duration so callers can apply the same long-press
+// behavior (chapter skip / orientation change) as the buttons. The center column
+// is left for the menu/Back gesture handled by each reader. Gated off the Xteink
+// devices (no touch) and behind the touchReaderControls setting; returns all-false
+// otherwise, so non-touch readers pay a single branch.
+struct TouchPageTurn {
+  bool prev;
+  bool next;
+  unsigned long heldMs;
+};
+
+inline TouchPageTurn detectTouchPageTurn(GfxRenderer& renderer) {
+  TouchPageTurn result{false, false, 0};
+  if (gpio.isXteinkDevice() || !SETTINGS.touchReaderControls) {
+    return result;
+  }
+  float nx = 0.0f, ny = 0.0f;
+  if (!gpio.wasTouchTap(nx, ny)) {
+    return result;
+  }
+  int lx = 0, ly = 0;
+  renderer.tapToLogical(nx, ny, lx, ly);
+  const int third = renderer.getScreenWidth() / 3;
+  if (lx < third) {
+    result.prev = true;
+  } else if (lx >= 2 * third) {
+    result.next = true;
+  }
+  result.heldMs = gpio.lastTouchHeldMs();
+  return result;
+}
+
 inline void displayWithRefreshCycle(const GfxRenderer& renderer, int& pagesUntilFullRefresh) {
   if (pagesUntilFullRefresh <= 1) {
     renderer.displayBuffer(HalDisplay::HALF_REFRESH);

src/activities/reader/TxtReaderActivity.cpp

@@ -72,7 +72,13 @@ void TxtReaderActivity::loop() {
     return;
   }
 
-  const auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
+  // Touch reader controls mirror the side page buttons (left third = back,
+  // right third = forward). No-op on Xteink / when the setting is off.
+  const auto touch = ReaderUtils::detectTouchPageTurn(renderer);
+
+  auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
+  prevTriggered = prevTriggered || touch.prev;
+  nextTriggered = nextTriggered || touch.next;
   if (!prevTriggered && !nextTriggered) {
     return;
   }

src/activities/reader/XtcReaderActivity.cpp

@@ -79,7 +79,14 @@ void XtcReaderActivity::loop() {
     return;
   }
 
-  const auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
+  // Touch reader controls mirror the side page buttons (left third = back,
+  // right third = forward, press-and-hold = chapter skip). No-op on Xteink /
+  // when the setting is off.
+  const auto touch = ReaderUtils::detectTouchPageTurn(renderer);
+
+  auto [prevTriggered, nextTriggered, fromTilt] = ReaderUtils::detectPageTurn(mappedInput);
+  prevTriggered = prevTriggered || touch.prev;
+  nextTriggered = nextTriggered || touch.next;
   if (!prevTriggered && !nextTriggered) {
     return;
   }
@@ -95,8 +102,9 @@ void XtcReaderActivity::loop() {
     return;
   }
 
-  const bool skipPages = !fromTilt && SETTINGS.longPressButtonBehavior == SETTINGS.CHAPTER_SKIP &&
-                         mappedInput.getHeldTime() > ReaderUtils::SKIP_HOLD_MS;
+  const unsigned long heldMs = (touch.prev || touch.next) ? touch.heldMs : mappedInput.getHeldTime();
+  const bool skipPages =
+      !fromTilt && SETTINGS.longPressButtonBehavior == SETTINGS.CHAPTER_SKIP && heldMs > ReaderUtils::SKIP_HOLD_MS;
   const int skipAmount = skipPages ? 10 : 1;
 
   if (prevTriggered) {