Unexpected Command History Block Behavior

Question

I wrote such a module to store the latest image changes in my drawing application in Delphi

    unit HistoryQueue;

    interface

    uses
      Graphics;

   type
myHistory = class
  constructor Create(Size:Integer);
  public
    procedure Push(Bmp:TBitmap);
    function Pop():TBitmap;
    procedure Clean();
    procedure Offset();
    function isEmpty():boolean;
    function isFull():boolean;
    function getLast():TBitmap;
  protected
    historyQueueArray: array of TBitmap;
    historyIndex, hSize:Integer;
  end;

implementation

procedure myHistory.Push(Bmp:TBitmap);
var tbmp:TBitmap;
begin
  if(not isFull) then begin
      Inc(historyIndex);
      historyQueueArray[historyIndex]:=TBitmap.Create;
      historyQueueArray[historyIndex].Assign(bmp);
  end else begin
      Offset();
      historyQueueArray[historyIndex]:=TBitmap.Create;
      historyQueueArray[historyIndex].Assign(bmp);
  end;

end;

procedure myHistory.Clean;
var i:Integer;
begin
{  for i:=0 to hSize do begin
    historyQueueArray[i].Free;
    historyQueueArray[i].Destroy;
  end;        }

end;

constructor myHistory.Create(Size:Integer);
begin
  hSize:=Size;
  SetLength(historyQueueArray, hSize);
  historyIndex:=-1;
end;

function myHistory.isEmpty: boolean;
begin
  Result:=(historyIndex = -1);
end;

function myHistory.isFull: boolean;
begin
  Result:=(historyIndex = hSize);
end;

procedure myHistory.Offset; {to handle overflow}
var i:integer;
begin
  //historyQueueArray[0]:=nil;
  for i:=0 to hSize-1 do begin
    historyQueueArray[i]:=TBitmap.Create;
    historyQueueArray[i].Assign(historyQueueArray[i+1]);
  end;
end;

function myHistory.Pop: TBitmap;
var
  popBmp:TBitmap;
begin
  popBmp:= TBitmap.Create;
  popBmp.Assign(historyQueueArray[historyIndex]);
  Dec(historyIndex);
  Result:=popBmp;
end;

function myHistory.getLast: TBitmap; {this function I use when I need refresh the cnvas when I draw ellipse or rect, to get rid of traces and safe previous changes of the picture}
var
  tBmp:TBitmap;
begin
  tBmp:= TBitmap.Create;
  tBmp.Assign(historyQueueArray[historyIndex]);
  Result:=tBmp;
end;

end.

And this is how I use it

procedure TMainForm.FormCreate(Sender: TObject);
var
  cleanBmp:TBitmap;
begin
    {...}

    doneRedo:=false;

    redomode:=false; undomode:=false;
//init arrays
    picHistory:=myHistory.Create(10);   //FOR UNDO
    tempHistory:=myHistory.Create(10); //FOR REDO

    cleanbmp:=TBitmap.Create;
    cleanbmp.Assign(imgMain.Picture.Bitmap);
    picHistory.Push(cleanbmp);
    cleanbmp.Free;

    {...}

end;

 procedure TMainForm.btnUndoClick(Sender: TObject);
var redBmp:TBitmap;
begin

  undoMode:=true;
  //if there were some changes
  if(not picHistory.isEmpty) then begin
    redBmp:=TBitmap.Create;
    redBmp.Assign(picHistory.getLast);
    //clean canvas
    imgMain.Picture.Bitmap:=nil; 
    //get what was there before
    imgMain.Canvas.Draw(0,0, picHistory.Pop);
    //and in case if we will not make any changes after UNDO(clicked one or more times)
    //and call REDO then
    tempHistory.Push(redBmp);//we save what were on canvas before UNDOand push it to redo history
    redBmp.Free;
  end;

end;


procedure TMainForm.btnRedoClick(Sender: TObject);
var undBmp:TBitmap;
begin
  redoMode:=true;
  if(not tempHistory.isEmpty) then begin

    doneRedo:=True;

    undBmp:=TBitmap.Create;

    undBmp.Assign(tempHistory.getLast);
    imgMain.Picture.Bitmap:=nil;
    MainForm.imgMain.Canvas.Draw(0,0, tempHistory.Pop);

    //same history (like with UNDO implementation) here but reverse
    picHistory.Push(undBmp);
    undBmp.Free;
  end;
end;


{...}

procedure TMainForm.imgMainMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var bmp:TBitmap;
begin
//if mouse were down and then it up this means we drew something
//and must save changes into history to be able to make UNDO
  {...}
    bmp:=TBitmap.Create;
    try
      bmp.Assign(imgMain.Picture.Bitmap);
      picHistory.Push(bmp);
      //if there are some changes added after redo then we clean redo history
     if (doneRedo) then begin
        tempHistory.Clean;
        doneRedo:=false;
     end;
    finally
      bmp.Free;
      //sor of refresh
      imgMain.Canvas.Draw(0,0, picHistory.getLast);
    end;
  {...}

But the problem is that this does not work as I expected. example:

If I press the cancel button once, nothing happens. Twice - he does what you need right away.

And if I draw an ellipse, then cancel once and start drawing a new one - the last drawn ellipse just disappears!

Here's an elipse drawing method in case it would be helpful to find out the problem

    procedure TMainForm.ellipseDraw(X, Y: Integer);
    begin
      imgMain.Canvas.Pen.Color:=useColor;
      imgMain.Canvas.Brush.Color:=scndColor;

      imgMain.Canvas.Pen.Width:=size;

      if(mouseIsDown) then  begin
        imgMain.Canvas.Draw(0,0, picHistory.getLast); //there gonna be no bizzare traces from figures
        imgMain.Canvas.Ellipse(dX, dY, X,Y);
      end;
    end;

Answer 1

Answer

- . - , .

, :

• imgMainMouseUp
• btnUndoClick , , .

- - .

Bonus

, Bitmaps, :

• Pop getLast Bitmap. . MainForm , . , .
• Offset . Queue[I] Queue[I + 1].
• Push .
• , Clean, . , , Clean.

, . :

• , isFull True, . Result := historyIndex = hSize - 1;
• (FIFO), (LIFO).
• Pop .

, :

uses
  SysUtils, Graphics;

type
  TBitmapHistory = class(TObject)
  private
    FIndex: Integer;
    FStack: array of TBitmap;
    procedure Offset;
  public
    procedure Clear;
    function Count: Integer;
    constructor Create(ACount: Integer);
    destructor Destroy; override;
    function Empty: Boolean;
    function Full: Boolean;
    function Last: TBitmap;
    function Pop: TBitmap;
    procedure Push(ABitmap: TBitmap);
  end;

implementation

{ TBitmapHistory }

procedure TBitmapHistory.Clear;
var
  I: Integer;
begin
  for I := 0 to Count - 1 do
    FreeAndNil(FStack[I]);
  FIndex := -1;
end;

function TBitmapHistory.Count: Integer;
begin
  Result := Length(FStack);
end;

constructor TBitmapHistory.Create(ACount: Integer);
begin
  inherited Create;
  SetLength(FStack, ACount);
  FIndex := -1;
end;

destructor TBitmapHistory.Destroy;
begin
  Clear;
  inherited Destroy;
end;

function TBitmapHistory.Empty: Boolean;
begin
  Result := FIndex = -1;
end;

function TBitmapHistory.Full: Boolean;
begin
  Result := FIndex = Count - 1;
end;

function TBitmapHistory.Last: TBitmap;
begin
  if Empty then
    Result := nil
  else
    Result := FStack[FIndex];
end;

procedure TBitmapHistory.Offset;
begin
  FStack[0].Free;
  Move(FStack[1], FStack[0], (Count - 1) * SizeOf(TBitmap));
end;

function TBitmapHistory.Pop: TBitmap;
begin
  if not Empty then
  begin
    Result := Last;
    Dec(FIndex);
  end;
end;

procedure TBitmapHistory.Push(ABitmap: TBitmap);
begin
  if Full then
    Offset
  else
    Inc(FIndex);
  FStack[Findex].Free;
  FStack[FIndex] := TBitmap.Create;
  FStack[Findex].Assign(ABitmap);
end;

:

• Contnrs TObjectStack, /.
• MainForm, , .