Converts the logical coordinates to the serial position. The serial position is the zero-based index of the character from the beginning of the entire text. You can send this message explicitly or use the Editor_LogicalToSerial inline function.
wParam = 0;
lParam = (LPARAM) (POINT_PTR*) pptLogical
Pointer to a POINT_PTR structure that specifies the logical coordinates to be converted.
Return the serial position.