Change description scroll message behaviour (#950)

* Refactor: Extract common scroll message code

* Change desc. scrolling to stop at the start and end

* Extract `ScrollMessage` to its own file

source/Core/Src/ScrollMessage.cpp

@@ -0,0 +1,68 @@
+#include "ScrollMessage.hpp"
+
+#include "OLED.hpp"
+#include "configuration.h"
+
+/**
+ * Counts the number of chars in the string excluding the null terminator.
+ * This is a custom version of `strlen` which takes into account our custom
+ * double-byte char encoding.
+ * @param str The input string.
+ * @return The length of the string.
+ */
+static uint16_t str_display_len(const char *const str) {
+  const uint8_t *next  = reinterpret_cast<const uint8_t *>(str);
+  uint16_t       count = 0;
+  while (next[0]) {
+    if (next[0] <= 0xF0) {
+      count++;
+      next++;
+    } else {
+      if (!next[1]) {
+        break;
+      }
+      count++;
+      next += 2;
+    }
+  }
+  return count;
+}
+
+uint16_t ScrollMessage::messageWidth(const char *message) { return FONT_12_WIDTH * str_display_len(message); }
+
+bool ScrollMessage::drawUpdate(const char *message, uint32_t currentTick) {
+  bool lcdRefresh = false;
+
+  if (messageStart == 0) {
+    messageStart = currentTick;
+    lcdRefresh   = true;
+  }
+  int16_t  messageOffset;
+  uint16_t msgWidth = messageWidth(message);
+  if (msgWidth > OLED_WIDTH) {
+    messageOffset = ((currentTick - messageStart) / (systemSettings.descriptionScrollSpeed == 1 ? TICKS_100MS / 10 : (TICKS_100MS / 5)));
+    messageOffset %= msgWidth + OLED_WIDTH; // Roll around at the end
+    if (messageOffset < OLED_WIDTH) {
+      // Snap the message to the left edge.
+      messageOffset = OLED_WIDTH;
+    } else if (messageOffset > msgWidth) {
+      // Snap the message to the right edge.
+      messageOffset = msgWidth;
+    }
+  } else {
+    // Centre the message without scrolling.
+    messageOffset = (OLED_WIDTH - msgWidth) / 2 + msgWidth;
+  }
+
+  if (lastOffset != messageOffset) {
+    OLED::clearScreen();
+
+    //^ Rolling offset based on time
+    OLED::setCursor((OLED_WIDTH - messageOffset), 0);
+    OLED::print(message, FontStyle::LARGE);
+    lastOffset = messageOffset;
+    lcdRefresh = true;
+  }
+
+  return lcdRefresh;
+}