Fix endian DGUS WriteVariable (#18703)

Marlin/src/lcd/extui/lib/dgus/DGUSDisplay.cpp

 }
 
 void DGUSDisplay::WriteVariable(uint16_t adr, uint16_t value) {
+  value = (value & 0xffU) << 8U | (value >> 8U);
   WriteVariable(adr, static_cast<const void*>(&value), sizeof(uint16_t));
 }
 
+void DGUSDisplay::WriteVariable(uint16_t adr, int16_t value) {
+  value = (value & 0xffU) << 8U | (value >> 8U);
+  WriteVariable(adr, static_cast<const void*>(&value), sizeof(uint16_t));
+}
+
+void DGUSDisplay::WriteVariable(uint16_t adr, uint8_t value) {
+  WriteVariable(adr, static_cast<const void*>(&value), sizeof(uint8_t));
+}
+
+void DGUSDisplay::WriteVariable(uint16_t adr, long value) {
+    union { long l; char lb[4]; } endian;
+    char tmp[4];
+    endian.l = value;
+    tmp[0] = endian.lb[3];
+    tmp[1] = endian.lb[2];
+    tmp[2] = endian.lb[1];
+    tmp[3] = endian.lb[0];
+    WriteVariable(adr, static_cast<const void*>(&tmp), sizeof(long));
+}
+
 void DGUSDisplay::WriteVariablePGM(uint16_t adr, const void* values, uint8_t valueslen, bool isstr) {
   const char* myvalues = static_cast<const char*>(values);
   bool strend = !myvalues;

Marlin/src/lcd/extui/lib/dgus/DGUSDisplay.h

   // Variable access.
   static void WriteVariable(uint16_t adr, const void* values, uint8_t valueslen, bool isstr=false);
   static void WriteVariablePGM(uint16_t adr, const void* values, uint8_t valueslen, bool isstr=false);
+  static void WriteVariable(uint16_t adr, int16_t value);
   static void WriteVariable(uint16_t adr, uint16_t value);
+  static void WriteVariable(uint16_t adr, uint8_t value);
+  static void WriteVariable(uint16_t adr, long value);
 
   // Until now I did not need to actively read from the display. That's why there is no ReadVariable
   // (I extensively use the auto upload of the display)

Marlin/src/lcd/extui/lib/dgus/DGUSScreenHandler.cpp

   if (var.memadr) {
     //DEBUG_ECHOPAIR(" DGUS_LCD_SendWordValueToDisplay ", var.VP);
     //DEBUG_ECHOLNPAIR(" data ", *(uint16_t *)var.memadr);
-    uint8_t *tmp = (uint8_t *) var.memadr;
-    uint16_t data_to_send = (tmp[0] << 8);
-    if (var.size >= 1) data_to_send |= tmp[1];
-    dgusdisplay.WriteVariable(var.VP, data_to_send);
+    if (var.size > 1)
+      dgusdisplay.WriteVariable(var.VP, *(int16_t*)var.memadr);
+    else
+      dgusdisplay.WriteVariable(var.VP, *(int8_t*)var.memadr);
   }
 }
 
     //DEBUG_ECHOLNPAIR(" data ", *(uint16_t *)var.memadr);
     uint16_t tmp = *(uint8_t *) var.memadr +1 ; // +1 -> avoid rounding issues for the display.
     tmp = map(tmp, 0, 255, 0, 100);
-    uint16_t data_to_send = swap16(tmp);
-    dgusdisplay.WriteVariable(var.VP, data_to_send);
+    dgusdisplay.WriteVariable(var.VP, tmp);
   }
 }
 
   //DEBUG_ECHOPAIR(" DGUSLCD_SendPrintProgressToDisplay ", var.VP);
   uint16_t tmp = ExtUI::getProgress_percent();
   //DEBUG_ECHOLNPAIR(" data ", tmp);
-  uint16_t data_to_send = swap16(tmp);
-  dgusdisplay.WriteVariable(var.VP, data_to_send);
+  dgusdisplay.WriteVariable(var.VP, tmp);
 }
 
 // Send the current print time to the display.
       DEBUG_ECHOLNPAIR(" data ", *(uint8_t *)var.memadr);
       uint16_t data_to_send = 0;
       if (*(uint8_t *) var.memadr) data_to_send = 1;
-      data_to_send = swap16(data_to_send);
       dgusdisplay.WriteVariable(var.VP, data_to_send);
     }
   }
     DEBUG_ECHOLNPAIR(" data ", *(int16_t *)var.memadr);
     uint16_t data_to_send = 0;
     if (*(int16_t *) var.memadr) data_to_send = 1;
-    data_to_send = swap16(data_to_send);
     dgusdisplay.WriteVariable(var.VP, data_to_send);
   }
 }
     //DEBUG_ECHOPAIR(" DGUSLCD_SendWaitingStatusToDisplay ", var.VP);
     //DEBUG_ECHOLNPAIR(" data ", swap16(index));
     if (period++ > DGUS_UI_WAITING_STATUS_PERIOD) {
-      dgusdisplay.WriteVariable(var.VP, swap16(index));
+      dgusdisplay.WriteVariable(var.VP, index);
       //DEBUG_ECHOLNPAIR(" data ", swap16(index));
       if (++index >= DGUS_UI_WAITING_STATUS) index = 0;
       period = 0;

Marlin/src/lcd/extui/lib/dgus/DGUSScreenHandler.h

     if (var.memadr) {
       float f = *(float *)var.memadr;
       f *= cpow(10, decimals);
-      union { long l; char lb[4]; } endian;
-
-      char tmp[4];
-      endian.l = f;
-      tmp[0] = endian.lb[3];
-      tmp[1] = endian.lb[2];
-      tmp[2] = endian.lb[1];
-      tmp[3] = endian.lb[0];
-      dgusdisplay.WriteVariable(var.VP, tmp, 4);
+      dgusdisplay.WriteVariable(var.VP, (long)f);
     }
   }
 
       float f = *(float *)var.memadr;
       DEBUG_ECHOLNPAIR_F(" >> ", f, 6);
       f *= cpow(10, decimals);
-      union { int16_t i; char lb[2]; } endian;
-
-      char tmp[2];
-      endian.i = f;
-      tmp[0] = endian.lb[1];
-      tmp[1] = endian.lb[0];
-      dgusdisplay.WriteVariable(var.VP, tmp, 2);
+      dgusdisplay.WriteVariable(var.VP, (int16_t)f);
     }
   }