Fix interpretation of negative numbers from DWIN #209

Author: Sebazzz

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

@@ -964,12 +964,14 @@ void DGUSScreenHandler::HandleMeshPoint(DGUS_VP_Variable &var, void *val_ptr) {
   const uint8_t x = probe_point / col_size; // Will be 0 to 3 inclusive
   const uint8_t y = (probe_point - (x * col_size)) / MESH_INPUT_DATA_SIZE;
 
-  float z = swap16(*(int16_t*)val_ptr) * 0.001;
+  int16_t rawZ = *(int16_t*)val_ptr;
+  float z = swap16(rawZ) * 0.001;
 
   SERIAL_ECHOPAIR("Overriding mesh value. X:", x);
   SERIAL_ECHOPAIR(" Y:", y);
   SERIAL_ECHOPAIR_F(" Z:", z);
-  SERIAL_ECHOPAIR(" [point ", probe_point, "] ");
+  SERIAL_ECHOPAIR(" [raw: ", rawZ);
+  SERIAL_ECHOPAIR("] [point ", probe_point, "] ");
   SERIAL_ECHOPAIR(" [VP: ", var.VP);
   SERIAL_ECHOLN("]");
 

Marlin/src/lcd/extui/lib/dgus_creality/DGUSVPVariable.h

@@ -51,6 +51,8 @@ struct DGUS_VP_Variable {
 // endianness swap
 FORCE_INLINE uint16_t swap16(const uint16_t value) { return (value & 0xffU) << 8U | (value >> 8U); }
 
+FORCE_INLINE int16_t swap16(const int16_t value) { return (value & 0xffU) << 8U | (value >> 8U); }
+
 FORCE_INLINE uint32_t swap32(const uint32_t value) { return ((value>>24)&0xff) |  ((value<<8)&0xff0000) | ((value>>8)&0xff00) | ((value<<24)&0xff000000); }
 
 FORCE_INLINE uint16_t uInt16Value(void *val_ptr) { return swap16(*static_cast<uint16_t*>(val_ptr)); }