Fix input lag: add PM_NOYIELD, skip idle GetDC, eliminate redundant renders

PeekMessage without PM_NOYIELD surrenders the timeslice on every empty
queue check (~55ms per yield in Win16).  Adding pm_NoYield keeps the
polling loop hot so keystrokes and serial echoes are processed without
scheduler delays.

FlipToScreen was calling GetDC/ReleaseDC on every loop iteration even
with zero dirty rows.  Added early-exit scan before acquiring a DC.

TickBlink was calling FlipToScreen redundantly (main loop also calls it).
Removed the FlipToScreen from TickBlink and reordered the main loop to
TickBlink (dirty only) then FlipToScreen (single render pass).

Also: removed FBlinkOn := True reset from ParseData (was dirtying the
cursor row on every incoming chunk), added WriteDeferred for parse-only
without render, moved FlipToScreen from private to public, added Show
call before entering the polling loop.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

delphi/KPANSI.PAS

@@ -134,7 +134,6 @@ type
     procedure EraseLine(Mode: Integer);
     procedure ExecuteCSI(FinalCh: Char);
     procedure ExecuteMusic;
-    procedure FlipToScreen;
     procedure FreeLineList(List: TList);
     function  GetCursorCol: Integer;
     function  GetCursorRow: Integer;
@@ -166,8 +165,10 @@ type
     destructor Destroy; override;
     procedure Clear;
     procedure Reset;
+    procedure FlipToScreen;
     procedure TickBlink;
     procedure Write(const S: string);
+    procedure WriteDeferred(const S: string);
     property CursorCol: Integer read GetCursorCol;
     property CursorRow: Integer read GetCursorRow;
   published
@@ -1222,6 +1223,7 @@ procedure TKPAnsi.FlipToScreen;
 var
   DC:       HDC;
   Row:      Integer;
+  HasDirty: Boolean;
 begin
   if not HandleAllocated then
     Exit;
@@ -1251,6 +1253,22 @@ begin
     FLastCursorRow := FCursorRow;
   end;
 
+  { Early exit: skip GetDC/ReleaseDC when nothing needs rendering }
+  if not FAllDirty then
+  begin
+    HasDirty := False;
+    for Row := 0 to FRows - 1 do
+    begin
+      if FDirtyRow[Row] then
+      begin
+        HasDirty := True;
+        Break;
+      end;
+    end;
+    if not HasDirty then
+      Exit;
+  end;
+
   { Interleaved render + blast: single buffer is reused per row }
   DC := GetDC(Handle);
   for Row := 0 to FRows - 1 do
@@ -1570,8 +1588,6 @@ begin
     FAllDirty       := True;
   end;
 
-  { Reset cursor blink to visible on new data }
-  FBlinkOn := True;
 end;
 
 
@@ -2315,7 +2331,6 @@ begin
     FBlinkOn       := not FBlinkOn;
     FTextBlinkOn   := not FTextBlinkOn;
     DirtyBlinkRows;
-    FlipToScreen;
   end;
 end;
 
@@ -2371,6 +2386,13 @@ begin
 end;
 
 
+procedure TKPAnsi.WriteDeferred(const S: string);
+begin
+  if Length(S) > 0 then
+    ParseData(S);
+end;
+
+
 { ----------------------------------------------------------------------- }
 { Component registration                                                   }
 { ----------------------------------------------------------------------- }

delphi/TESTMAIN.PAS

@@ -169,11 +169,12 @@ var
   Msg: TMsg;
   S:   string;
 begin
+  Show;
   FDone := False;
   while not FDone do
   begin
     { Process all pending Windows messages (keyboard, paint, scrollbar) }
-    while PeekMessage(Msg, 0, 0, 0, pm_Remove) do
+    while PeekMessage(Msg, 0, 0, 0, pm_Remove or pm_NoYield) do
     begin
       if Msg.message = wm_Quit then
       begin
@@ -187,18 +188,17 @@ begin
     if FDone then
       Break;
 
-    { Poll serial data directly -- no WM_COMMNOTIFY, no events }
+    { Poll serial data -- read one chunk, then yield to messages }
     if FComm.PortOpen then
     begin
-      repeat
       S := FComm.Input;
       if Length(S) > 0 then
-          FAnsi.Write(S);
-      until Length(S) = 0;
+        FAnsi.WriteDeferred(S);
     end;
 
-    { Tick blink state (uses GetTickCount, no WM_TIMER) }
+    { Tick blink (dirties rows if interval elapsed), then render }
     FAnsi.TickBlink;
+    FAnsi.FlipToScreen;
   end;
 end;