Fix for random uninitialized data in display RAM for displays less than 128 segments wide.

Bug was visible when scrolling.
TDB: allow drawing outside visible area to exploit full 128 horizontal resolution in hardware scrolling.

Author: dok-net

Adafruit_SSD1306.cpp

@@ -451,7 +451,7 @@ void Adafruit_SSD1306::ssd1306_command(uint8_t c) {
 boolean Adafruit_SSD1306::begin(uint8_t vcs, uint8_t addr, boolean reset,
   boolean periphBegin) {
 
-  if((!buffer) && !(buffer = (uint8_t *)malloc(WIDTH * ((HEIGHT + 7) / 8))))
+  if((!buffer) && !(buffer = (uint8_t *)malloc(SSD1306_SEGMENTS * ((HEIGHT + 7) / 8))))
     return false;
 
   clearDisplay();
@@ -625,10 +625,11 @@ void Adafruit_SSD1306::drawPixel(int16_t x, int16_t y, uint16_t color) {
       y = HEIGHT - y - 1;
       break;
     }
+    if ((WIDTH == 64) && (HEIGHT == 48)) x += 32;
     switch(color) {
-     case WHITE:   buffer[x + (y/8)*WIDTH] |=  (1 << (y&7)); break;
-     case BLACK:   buffer[x + (y/8)*WIDTH] &= ~(1 << (y&7)); break;
-     case INVERSE: buffer[x + (y/8)*WIDTH] ^=  (1 << (y&7)); break;
+     case WHITE:   buffer[x + (y/8)* SSD1306_SEGMENTS] |=  (1 << (y&7)); break;
+     case BLACK:   buffer[x + (y/8)* SSD1306_SEGMENTS] &= ~(1 << (y&7)); break;
+     case INVERSE: buffer[x + (y/8)* SSD1306_SEGMENTS] ^=  (1 << (y&7)); break;
     }
   }
 }
@@ -641,7 +642,7 @@ void Adafruit_SSD1306::drawPixel(int16_t x, int16_t y, uint16_t color) {
             commands as needed by one's own application.
 */
 void Adafruit_SSD1306::clearDisplay(void) {
-  memset(buffer, 0, WIDTH * ((HEIGHT + 7) / 8));
+  memset(buffer, 0, SSD1306_SEGMENTS * ((HEIGHT + 7) / 8));
 }
 
 /*!
@@ -702,8 +703,9 @@ void Adafruit_SSD1306::drawFastHLineInternal(
       w = (WIDTH - x);
     }
     if(w > 0) { // Proceed only if width is positive
-      uint8_t *pBuf = &buffer[(y / 8) * WIDTH + x],
-               mask = 1 << (y & 7);
+      if ((WIDTH == 64) && (HEIGHT == 48)) x += 32;
+      uint8_t* pBuf = &buffer[x + (y / 8) * SSD1306_SEGMENTS];
+      uint8_t mask = 1 << (y & 7);
       switch(color) {
        case WHITE:               while(w--) { *pBuf++ |= mask; }; break;
        case BLACK: mask = ~mask; while(w--) { *pBuf++ &= mask; }; break;
@@ -774,7 +776,8 @@ void Adafruit_SSD1306::drawFastVLineInternal(
       // this display doesn't need ints for coordinates,
       // use local byte registers for faster juggling
       uint8_t  y = __y, h = __h;
-      uint8_t *pBuf = &buffer[(y / 8) * WIDTH + x];
+      if ((WIDTH == 64) && (HEIGHT == 48)) x += 32;
+      uint8_t *pBuf = &buffer[x + (y / 8) * SSD1306_SEGMENTS];
 
       // do the first partial byte, if necessary - this requires some masking
       uint8_t mod = (y & 7);
@@ -795,7 +798,7 @@ void Adafruit_SSD1306::drawFastVLineInternal(
          case BLACK:   *pBuf &= ~mask; break;
          case INVERSE: *pBuf ^=  mask; break;
         }
-        pBuf += WIDTH;
+        pBuf += SSD1306_SEGMENTS;
       }
 
       if(h >= mod) { // More to go?
@@ -807,15 +810,15 @@ void Adafruit_SSD1306::drawFastVLineInternal(
             // black/white write version with an extra comparison per loop
             do {
               *pBuf ^= 0xFF;  // Invert byte
-              pBuf  += WIDTH; // Advance pointer 8 rows
+              pBuf  += SSD1306_SEGMENTS; // Advance pointer 8 rows
               h     -= 8;     // Subtract 8 rows from height
             } while(h >= 8);
           } else {
             // store a local value to work with
             uint8_t val = (color != BLACK) ? 255 : 0;
             do {
               *pBuf = val;    // Set byte
-              pBuf += WIDTH;  // Advance pointer 8 rows
+              pBuf += SSD1306_SEGMENTS;  // Advance pointer 8 rows
               h    -= 8;      // Subtract 8 rows from height
             } while(h >= 8);
           }
@@ -895,27 +898,16 @@ uint8_t *Adafruit_SSD1306::getBuffer(void) {
 */
 void Adafruit_SSD1306::display(void) {
   TRANSACTION_START
-  if ((WIDTH != 64) || (HEIGHT != 48)) {
-    static const uint8_t PROGMEM dlist1a[] = {
-      SSD1306_PAGEADDR,
-      0,                         // Page start address
-      0xFF,                      // Page end (not really, but works here)
-      SSD1306_COLUMNADDR,
-      0 };                       // Column start address
-    ssd1306_commandList(dlist1a, sizeof(dlist1a));
-    ssd1306_command1(WIDTH - 1); // Column end address
-  } else {
-    static const uint8_t PROGMEM dlist1b[] = {
-      SSD1306_PAGEADDR,
-      0 };                       // Page start address
-    ssd1306_commandList(dlist1b, sizeof(dlist1b));
-    ssd1306_command1((HEIGHT / 8) - 1); // Page end address
-    static const uint8_t PROGMEM dlist2b[] = {
-      SSD1306_COLUMNADDR,
-      32 };                       // Column start address
-    ssd1306_commandList(dlist2b, sizeof(dlist2b));
-    ssd1306_command1(32 + WIDTH - 1); // Column end address
-  }
+  static const uint8_t PROGMEM dlist1[] = {
+    SSD1306_PAGEADDR,
+    0 };                       // Page start address
+  ssd1306_commandList(dlist1, sizeof(dlist1));
+  ssd1306_command1((HEIGHT + 7) / 8 - 1); // Page end address
+  static const uint8_t PROGMEM dlist2[] = {
+    SSD1306_COLUMNADDR,
+    0 };                       // Column start address
+  ssd1306_commandList(dlist2, sizeof(dlist2));
+  ssd1306_command1(SSD1306_SEGMENTS - 1); // Column end address
 
 #if defined(ESP8266)
   // ESP8266 needs a periodic yield() call to avoid watchdog reset.
@@ -926,7 +918,7 @@ void Adafruit_SSD1306::display(void) {
   // 32-byte transfer condition below.
   yield();
 #endif
-  uint16_t count = WIDTH * ((HEIGHT + 7) / 8);
+  uint16_t count = SSD1306_SEGMENTS * ((HEIGHT + 7) / 8);
   uint8_t *ptr   = buffer;
   if(wire) { // I2C
     wire->beginTransmission(i2caddr);

Adafruit_SSD1306.h

@@ -95,6 +95,8 @@
 #define SSD1306_ACTIVATE_SCROLL                      0x2F ///< Start scroll
 #define SSD1306_SET_VERTICAL_SCROLL_AREA             0xA3 ///< Set scroll range
 
+#define SSD1306_SEGMENTS			128 ///< See datasheet
+
 // Deprecated size stuff for backwards compatibility with old sketches
 #if defined SSD1306_128_64
  #define SSD1306_LCDWIDTH  128 ///< DEPRECATED: width w/SSD1306_128_64 defined
@@ -140,11 +142,11 @@ class Adafruit_SSD1306 : public Adafruit_GFX {
                  boolean periphBegin=true);
   void         display(void);
   void         clearDisplay(void);
-  void         invertDisplay(boolean i);
+  virtual void invertDisplay(boolean i) override;
   void         dim(boolean dim);
-  void         drawPixel(int16_t x, int16_t y, uint16_t color);
-  virtual void drawFastHLine(int16_t x, int16_t y, int16_t w, uint16_t color);
-  virtual void drawFastVLine(int16_t x, int16_t y, int16_t h, uint16_t color);
+  virtual void drawPixel(int16_t x, int16_t y, uint16_t color) override;
+  virtual void drawFastHLine(int16_t x, int16_t y, int16_t w, uint16_t color) override;
+  virtual void drawFastVLine(int16_t x, int16_t y, int16_t h, uint16_t color) override;
   void         startscrollright(uint8_t start, uint8_t stop);
   void         startscrollleft(uint8_t start, uint8_t stop);
   void         startscrolldiagright(uint8_t start, uint8_t stop);