Show activity indicator while the main thread is blocked (continue)

Question

Continue with previous question I want to be able to show some activity indicator even if the main thread is blocked. (based on this article).

Problems

Answer 1

Initially this always crashed. Then I found the solution:

1) Wrap the while loop inside a try-finally structure with FBitmap.Canvas.Lock;:

FBitmap.Canvas.Lock;
try
  while not Terminated do
  begin
    with FBitmap.Canvas do
    begin
      StretchDraw(FImageRect, FbkPattern);
      case State of
        incRight:
          begin
            Inc(Right, Increment);
            if Right > FImageRect.Right then
            begin
              Right := FImageRect.Right;
              Inc(State);
            end;
          end;
        incLeft:
          begin
            Inc(Left, Increment);
            if Left >= Right then
            begin
              Left := Right;
              Inc(State);
            end;
          end;
        decLeft:
          begin
            Dec(Left, Increment);
            if Left <= 0 then
            begin
              Left := 0;
              Inc(State);
            end;
          end;
        decRight:
          begin
            Dec(Right, Increment);
            if Right <= 0 then
            begin
              Right := 0;
              State := incRight;
            end;
          end;
      end;

      StretchDraw(Rect(Left, FImageRect.Top, Right, FImageRect.Bottom), FfgPattern);
    end; { with }

    // Synchronize(PaintTargetWindow); // not painting when the main thread is blocked
    PaintTargetWindow;

    SleepEx(FInterval, False);
  end; { While }
finally
  FBitmap.Canvas.Unlock;
end;

2) In FormCreate of your application call this procedure:

procedure DisableProcessWindowsGhosting;
var
  DisableProcessWindowsGhostingProc: procedure;
begin
  DisableProcessWindowsGhostingProc := GetProcAddress(GetModuleHandle('user32.dll'), 'DisableProcessWindowsGhosting');
  if Assigned(DisableProcessWindowsGhostingProc) then
    DisableProcessWindowsGhostingProc;
end;

Now it works perfectly - never crashed so far! Delphi XE2, Win7 x64