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Looking for fast "PutPixel" procedure

numbercrunch asked
Medium Priority
Last Modified: 2012-06-27
I am looking for an efficient way to set pixels in a bitmap or on a canvas (Delphi 2.) Executing Bitmap.Canvas.Pixels[x,y]:=clBlack" is very slow - it does about 60,000 pixels/second on my 166Mhz Pentium. In my application, I do about 22 extended arithmetic operations per pixel (including sqrt/sin/cos), and even then the Pixels property takes 8 times longer to execute than my code. In the past under DOS, the time to "PutPixel" was a tiny fraction of the calculation time. I cannot construct the image I am building using any other method such as lines, etc.

I thought that creating a bitmap in memory would be faster than plotting directly to the canvas, but it isn't. An outline of my code is:

    Bitmap := TBitMap.Create;
    Bitmap.Height := Image1.Height;
    Bitmap.Width := Image1.Width;
    { Do calculations and call this approx 40,000 times: }
        Bitmap.Canvas.Pixels[x,y] := clBlack;
    Image1.Picture.Graphic := Bitmap;

I have tried various options such as "IgnorePalette := True", but it makes no difference.

Does anybody know of a way of getting to the bitmap in memory? I am sure I could write code to "twiddle bits" there much faster than the Pixels property. Or is there any other way?
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Most of the newsgroups say that on screen images are the fastest and that by doing it off screen, your procedures will be about 3 times slower than an onscreen edit.  They also recommend using a function called CreateDIBSection to create your bitmap and to edit it by pointer to each bit.  I've never done it, but that is what they recommend.  If you want to see the discussion, goto Alta Vista and search the UseNet for: fast delphi bitmap

Good Luck,
I reckon you've got no chance. I've done a lot of personal
research into this - I tried all dos ways of putting pixels
(Int 10h, Mem) Etc, and using the ASM command,
eving setting up an array directly in segA000. Your only hope
is with a bitmap of some description.

You can use Memory Image of Bitmap and then use SetDIBits function to apply changes.
This is example of this.

unit Unit1;


  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,
  Forms, Dialogs, StdCtrls, Buttons, ExtCtrls;

 XSize = 4*63; { must be devided by 4 !!!}
 YSize = 250;

  TForm1 = class(TForm)
    BitBtn1: TBitBtn;
    PaintBox1: TPaintBox;
    Label1: TLabel;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure BitBtn1Click(Sender: TObject);
    ByteInfo : PBitmapInfo;
    ByteBits : array[0..YSize-1,0..XSize-1] of byte;
  public {}

  Form1: TForm1;


{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
 i,j : longint;
 for j:=0 to YSize-1 do
   for i:=0 to XSize-1 do
     ByteBits[j,i]:=Random(255); { here is filling byte array }

 { Create BitmapInfoHeader for 256 color bitmap }
 GetMem( ByteInfo, SizeOf(TBitmapInfoHeader) + 256*SizeOf(TRGBQuad) );
 ByteInfo^.BmiHeader.biSize := SizeOf(TBitmapInfoHeader);
 ByteInfo^.BmiHeader.biWidth := XSize;
 ByteInfo^.BmiHeader.biHeight := YSize;
 ByteInfo^.BmiHeader.biPlanes := 1;
 ByteInfo^.BmiHeader.biBitCount := 8; { 256 color }
 ByteInfo^.BmiHeader.biCompression := BI_RGB;
 ByteInfo^.BmiHeader.biSizeImage := 0;
 ByteInfo^.BmiHeader.biXPelsPerMeter:= 1000;
 ByteInfo^.BmiHeader.biYPelsPerMeter:= 1000;
 ByteInfo^.BmiHeader.biClrUsed:= 0;
 ByteInfo^.BmiHeader.biClrImportant:= 0;
 for i:=0   to 255 do
   ByteInfo^.BmiColors[i].rgbRed := Random(255);
   ByteInfo^.BmiColors[i].rgbGreen := Random(255);
   ByteInfo^.BmiColors[i].rgbBlue := Random(255);
   ByteInfo^.BmiColors[i].rgbReserved := 0;

procedure TForm1.FormDestroy(Sender: TObject);
  FreeMem( ByteInfo, SizeOf(TBitmapInfoHeader) + 256*SizeOf(TRGBQuad) );

procedure TForm1.BitBtn1Click(Sender: TObject);
 Bmp : HBitmap;
 NewDC : HDC;
 T1 : TDateTime;
 i,j,k : integer;
 Count : integer;
 NewDC := CreateCompatibleDC( PaintBox1.Canvas.Handle );
 Bmp := CreateCompatibleBitmap( PaintBox1.Canvas.Handle, XSize, YSize );
 SelectObject( NewDC, Bmp );
 Count := 50;
 for i:=1 to Count do
   SetDIBits( NewDC, Bmp, 0, YSize, @ByteBits, ByteInfo^, DIB_RGB_Colors );
   BitBlt( PaintBox1.Canvas.Handle, 0, 0, XSize, YSize, NewDC, 0, 0, SrcCopy );
   for j:=0 to YSize-1 do
   for k:=0 to XSize-1 do
     ByteBits[j,k] := ByteBits[j,k+1];
 DeleteObject( Bmp );
 DeleteDC( NewDC );
 Label1.Caption := 'Time=' + FormatFloat('#.000',(Now-t1)*100000*1000/(Count*YSize*XSize))+
                   'ms for one pixel''s read+write';


If You need modify existing  bitmap then of course you can use GetDIBits and then this example.


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Thank you Mirek!! I have not yet tried this code, but at last I
have a working example to build from! I will let you know what
success I have.
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