slightly cursed but we save 160 bytes

src/LCDDisplay.cpp

@@ -60,7 +60,6 @@ void LCDDisplay::setBacklight(uint8_t brightness) {
     write(_lcd, &cmdbuf, brightness ? 3 : 2);
 }
 
-
 void LCDDisplay::setCursor(uint8_t row, uint8_t col) {
     uint8_t cmdbuf[] = {254, 71, (uint8_t)(col + 1), (uint8_t)(row + 1)};
     write(_lcd, &cmdbuf, 4);
@@ -92,28 +91,25 @@ void LCDDisplay::writeLines(std::array<std::string, 4> lines) {
     writeStr(lines[2] + lines[3]);
 }
 
-/* writes string to line buffer at given pos*/
+/* writes string to write buffer at calculated pos */
 void LCDDisplay::writeBuf(uint8_t row, uint8_t col, std::string str) {
-    size_t len = std::min(str.size(), sizeof(linebuf[row]) - col);
-    std::memcpy(&linebuf[row][col], str.c_str(), len);  // will overflow
+    size_t len = std::min(str.size(), sizeof(writebuf) - col);
+    uint8_t pos = 4 + col + (40 * (row % 2));  // skip 4 bytes to leave room for set cursor command
+    if (row >= 2) pos += 84;                   // if we're writing to disp2, skip another 4 bytes for set cursor command and 2*40 bytes of disp 1
+    std::memcpy(&writebuf[pos], str.c_str(), len);
 }
 
 void LCDDisplay::clearBuf() {
-    std::memset(linebuf, ' ', sizeof(linebuf));
+    std::memset(writebuf, ' ', sizeof(writebuf));
 }
 
 /* hyper optimized buffer flush command, writes whole disp with a single write */
 void LCDDisplay::flushBuf() {
-    uint8_t writebuf[168];                // 4x40 chars + 2x4 setcursor commands
+    // we could skip all of this and set it in constructor if we were extra sure the lines wont ever exceed 40 chars
     uint8_t setDisp[] = {254, 71, 1, 1};  // set cursor to char 1, line 1
-
-    std::memcpy(&writebuf[0], setDisp, 4);        // copy set cursor command
-    std::memcpy(&writebuf[4], linebuf[0], 40);    // copy 1st line
-    std::memcpy(&writebuf[44], linebuf[1], 40);   // copy 2nd line
-    std::memcpy(&writebuf[84], setDisp, 3);       // copy set cursor command but skip the line byte
-    writebuf[87] = 3;                             // set cursor to 3rd line
-    std::memcpy(&writebuf[88], linebuf[2], 40);   // copy 3rd line
-    std::memcpy(&writebuf[128], linebuf[3], 40);  // copy 4th line
+    std::memcpy(&writebuf[0], setDisp, 4);
+    std::memcpy(&writebuf[84], setDisp, 4);
+    writebuf[87] = 3;  // overwrite set cursor c1 l1 to c1 l3
 
     write(_lcd, writebuf, 168);
 }