Merge pull request #219 from Professr/issue#154

Fixed #154 - Cleaned up UTF-8 conversion, tweaked screen.cpp to replace a hardcoded constant

src/screen.cpp

@@ -514,6 +514,9 @@ void Screen::setup()
     // Store a pointer to Screen so we can get to it from static functions.
     ui.getUiState()->userData = this;
 
+    // Set the utf8 conversion function
+    dispdev.setFontTableLookupFunction(customFontTableLookup);
+
     // Add frames.
     static FrameCallback bootFrames[] = {drawBootScreen};
     static const int bootFrameCount = sizeof(bootFrames) / sizeof(bootFrames[0]);
@@ -720,7 +723,7 @@ void DebugInfo::drawFrame(OLEDDisplay *display, OLEDDisplayUiState *state, int16
     }
 
     const char *fields[] = {channelStr, nullptr};
-    uint32_t yo = drawRows(display, x, y + 12, fields);
+    uint32_t yo = drawRows(display, x, y + FONT_HEIGHT, fields);
 
     display->drawLogBuffer(x, yo);
 }

src/screen.h

@@ -149,6 +149,37 @@ class Screen : public PeriodicTask
         }
     }
 
+    /// Overrides the default utf8 character conversion, to replace empty space with question marks
+    static char customFontTableLookup(const uint8_t ch) {
+        // UTF-8 to font table index converter
+        // Code form http://playground.arduino.cc/Main/Utf8ascii
+        static uint8_t LASTCHAR;
+        static bool SKIPREST;   // Only display a single unconvertable-character symbol per sequence of unconvertable characters
+
+        if (ch < 128) { // Standard ASCII-set 0..0x7F handling
+            LASTCHAR = 0;
+            SKIPREST = false;
+            return ch;
+        }
+
+        uint8_t last = LASTCHAR;   // get last char
+        LASTCHAR = ch;
+
+        switch (last) {    // conversion depnding on first UTF8-character
+            case 0xC2: { SKIPREST = false; return (uint8_t) ch; }
+            case 0xC3: { SKIPREST = false; return (uint8_t) (ch | 0xC0); }
+        }
+
+        // We want to strip out prefix chars for two-byte char formats
+        if (ch == 0xC2 || ch == 0xC3 || ch == 0x82) return (uint8_t) 0;
+
+        // If we already returned an unconvertable-character symbol for this unconvertable-character sequence, return NULs for the rest of it
+        if (SKIPREST) return (uint8_t) 0;
+        SKIPREST = true;
+
+        return (uint8_t) 191; // otherwise: return ¿ if character can't be converted (note that the font map we're using doesn't stick to standard EASCII codes)
+    }
+
     /// Returns a handle to the DebugInfo screen.
     //
     // Use this handle to set things like battery status, user count, GPS status, etc.