Want to win a PS4? Go Premium and enter to win our High-Tech Treats giveaway. Enter to Win

x
?
Solved

offscreen bitmaps

Posted on 1998-01-15
4
Medium Priority
?
531 Views
Last Modified: 2010-08-05
I want to construct a line offscreen and then display it over a bitmap with the picture showing through.
I always end up with a white background covering the bitmap.  Why?
eg.,

source:=rect(0,0,600,360);
dest:=rect(0,0,600,360);
offscreen:=tbitmap.create;
try
offscreen.width:=600;
offscreen.height:=360;
with offscreen.canvas do
begin
pen.color:=clred;
brush.color:=clwhite;
brush.style:=bsclear;
moveto(60,60);
lineto(250,300);
end;
paintbox1.canvas.copyrect(dest,offscreen.canvas,source);
finally
offscreen.free;
end;
0
Comment
Question by:nifty
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
4 Comments
 
LVL 5

Expert Comment

by:JimBob091197
ID: 1356891
Do you mean that your offscreen bitmap must have a transparent background?  If so, you have to make it draw tranparently onto your other bitmap.  If this is your case, I can give you code to draw transparently.

JB
0
 
LVL 8

Expert Comment

by:ZifNab
ID: 1356892
Yeah JimBob, I guess that's what nifty wants.
0
 
LVL 5

Accepted Solution

by:
JimBob091197 earned 200 total points
ID: 1356893
If that's the case, then this should be the answer:

const
  TransparentMask = $02000000;

function Min(i1, i2: Integer): Integer;
begin
      if (i1 < i2) then
            Result := i1
      else
            Result := i2;
end;

function Max(i1, i2: Integer): Integer;
begin
      if (i1 > i2) then
            Result := i1
      else
            Result := i2;
end;

function WidthOf(R: TRect): Integer;
begin
      Result := R.Right - R.Left;
end;

function HeightOf(R: TRect): Integer;
begin
      Result := R.Bottom - R.Top;
end;

procedure AdjustRect(var R: TRect; LeftChange, TopChange, RightChange, BottomChange: Integer);
begin
      Inc(R.Left, LeftChange);
      Inc(R.Top, TopChange);
      Inc(R.Right, RightChange);
      Inc(R.Bottom, BottomChange);
end;

procedure DrawTransparentBitmapRect(DC: HDC; Bitmap: HBitmap; xStart, yStart,
  Width, Height: Integer; Rect: TRect; TransparentColor: TColorRef);
var
      BM: Windows.TBitmap;
      cColor: TColorRef;
  bmAndBack, bmAndObject, bmAndMem, bmSave: HBitmap;
  bmBackOld, bmObjectOld, bmMemOld, bmSaveOld: HBitmap;
  hdcMem, hdcBack, hdcObject, hdcTemp, hdcSave: HDC;
  ptSize, ptRealSize, ptBitSize, ptOrigin: TPoint;
begin
  hdcTemp := CreateCompatibleDC(DC);
  SelectObject(hdcTemp, Bitmap);      { Select the bitmap    }
  GetObject(Bitmap, SizeOf(BM), @BM);
  ptRealSize.x := Min(Rect.Right - Rect.Left, BM.bmWidth - Rect.Left);
  ptRealSize.y := Min(Rect.Bottom - Rect.Top, BM.bmHeight - Rect.Top);
  DPtoLP(hdcTemp, ptRealSize, 1);
  ptOrigin.x := Rect.Left;
  ptOrigin.y := Rect.Top;
  DPtoLP(hdcTemp, ptOrigin, 1);       { Convert from device  }
                                      { to logical points    }
  ptBitSize.x := BM.bmWidth;          { Get width of bitmap  }
  ptBitSize.y := BM.bmHeight;         { Get height of bitmap }
  DPtoLP(hdcTemp, ptBitSize, 1);
  if (ptRealSize.x = 0) or (ptRealSize.y = 0) then begin
    ptSize := ptBitSize;
    ptRealSize := ptSize;
  end
  else ptSize := ptRealSize;
  if (Width = 0) or (Height = 0) then begin
    Width := ptSize.x;
    Height := ptSize.y;
  end;

  { Create some DCs to hold temporary data }
  hdcBack   := CreateCompatibleDC(DC);
  hdcObject := CreateCompatibleDC(DC);
  hdcMem    := CreateCompatibleDC(DC);
  hdcSave   := CreateCompatibleDC(DC);
  { Create a bitmap for each DC. DCs are required for a number of }
  { GDI functions                                                 }
  { Monochrome DC }
  bmAndBack   := CreateBitmap(ptSize.x, ptSize.y, 1, 1, nil);
  bmAndObject := CreateBitmap(ptSize.x, ptSize.y, 1, 1, nil);
  bmAndMem    := CreateCompatibleBitmap(DC, Max(ptSize.x, Width), Max(ptSize.y, Height));
  bmSave      := CreateCompatibleBitmap(DC, ptBitSize.x, ptBitSize.y);
  { Each DC must select a bitmap object to store pixel data }
  bmBackOld   := SelectObject(hdcBack, bmAndBack);
  bmObjectOld := SelectObject(hdcObject, bmAndObject);
  bmMemOld    := SelectObject(hdcMem, bmAndMem);
  bmSaveOld   := SelectObject(hdcSave, bmSave);
  { Set proper mapping mode }
  SetMapMode(hdcTemp, GetMapMode(DC));

  { Save the bitmap sent here, because it will be overwritten }
  BitBlt(hdcSave, 0, 0, ptBitSize.x, ptBitSize.y, hdcTemp, 0, 0, SRCCOPY);
  { Set the background color of the source DC to the color,         }
  { contained in the parts of the bitmap that should be transparent }
  cColor := SetBkColor(hdcTemp, TransparentColor);
  { Create the object mask for the bitmap by performing a BitBlt()  }
  { from the source bitmap to a monochrome bitmap                   }
  BitBlt(hdcObject, 0, 0, ptSize.x, ptSize.y, hdcTemp, ptOrigin.x, ptOrigin.y,
    SRCCOPY);
  { Set the background color of the source DC back to the original  }
  { color                                                           }
  SetBkColor(hdcTemp, cColor);
  { Create the inverse of the object mask }
  BitBlt(hdcBack, 0, 0, ptSize.x, ptSize.y, hdcObject, 0, 0,
    NOTSRCCOPY);
  { Copy the background of the main DC to the destination }
  BitBlt(hdcMem, 0, 0, Width, Height, DC, xStart, yStart,
    SRCCOPY);
  { Mask out the places where the bitmap will be placed }
  StretchBlt(hdcMem, 0, 0, Width, Height, hdcObject, 0, 0,
    ptSize.x, ptSize.y, SRCAND);
  {BitBlt(hdcMem, 0, 0, ptSize.x, ptSize.y, hdcObject, 0, 0, SRCAND);}
  { Mask out the transparent colored pixels on the bitmap }
  BitBlt(hdcTemp, ptOrigin.x, ptOrigin.y, ptSize.x, ptSize.y, hdcBack, 0, 0,
    SRCAND);
  { XOR the bitmap with the background on the destination DC }
  StretchBlt(hdcMem, 0, 0, Width, Height, hdcTemp, ptOrigin.x, ptOrigin.y,
    ptSize.x, ptSize.y, SRCPAINT);
  {BitBlt(hdcMem, 0, 0, ptSize.x, ptSize.y, hdcTemp, ptOrigin.x, ptOrigin.y,
    SRCPAINT);}
  { Copy the destination to the screen }
  BitBlt(DC, xStart, yStart, Max(ptRealSize.x, Width), Max(ptRealSize.y, Height),
    hdcMem, 0, 0, SRCCOPY);
  { Place the original bitmap back into the bitmap sent here }
  BitBlt(hdcTemp, 0, 0, ptBitSize.x, ptBitSize.y, hdcSave, 0, 0, SRCCOPY);

  { Delete the memory bitmaps }
  DeleteObject(SelectObject(hdcBack, bmBackOld));
  DeleteObject(SelectObject(hdcObject, bmObjectOld));
  DeleteObject(SelectObject(hdcMem, bmMemOld));
  DeleteObject(SelectObject(hdcSave, bmSaveOld));
  { Delete the memory DCs }
  DeleteDC(hdcMem);
  DeleteDC(hdcBack);
  DeleteDC(hdcObject);
  DeleteDC(hdcSave);
  DeleteDC(hdcTemp);
end;

procedure InternalDrawTransBmpRect(Dest: TCanvas; X, Y, W, H: Integer; Rect: TRect; Bitmap: TBitmap; TransparentColor: TColor);
var
  MemImage: TBitmap;
  R: TRect;
begin
  MemImage := TBitmap.Create;
  try
    R := Bounds(0, 0, Bitmap.Width, Bitmap.Height);
    if TransparentColor = clNone then begin
                  if (WidthOf(Rect) <> 0) and (HeightOf(Rect) <> 0) then R := Rect;
      MemImage.Width := WidthOf(R);
                  MemImage.Height := HeightOf(R);
      MemImage.Canvas.CopyRect(Bounds(0, 0, MemImage.Width, MemImage.Height),
        Bitmap.Canvas, R);
      if (W = 0) or (H = 0) then Dest.Draw(X, Y, MemImage)
      else Dest.StretchDraw(Bounds(X, Y, W, H), MemImage);
    end
    else  begin
      MemImage.Width := WidthOf(R);
                  MemImage.Height := HeightOf(R);
      MemImage.Canvas.CopyRect(R, Bitmap.Canvas, R);
      DrawTransparentBitmapRect(Dest.Handle, MemImage.Handle, X, Y, W, H,
        Rect, ColorToRGB(TransparentColor and not TransparentMask));
    end;
  finally
    MemImage.Free;
  end;
end;

procedure DrawBitmapTransparent(Dest: TCanvas; XOrigin, YOrigin: Integer; Bitmap: TBitmap; TransparentColor: TColor);
begin
      InternalDrawTransBmpRect(Dest, XOrigin, YOrigin, 0, 0, Rect(0, 0, 0, 0), Bitmap, TransparentColor);
end;



To use this code, suppose you have a TImage on your form called imgTest, with an existing picture inside it:

procedure DoStuff;
var
  Bmp: TBitmap;
begin
  Bmp := TBitmap.Create;
  Bmp.Width := imgTest.Width;
  Bmp.Height := imgTest.Height;
  with Bmp.Canvas do
    begin
      Brush.Color := clYellow;  // This is the transparent color.
      FillRect(Rect(0, 0, imgTest.Width, imgTest.Height));
      Pen.Color := clRed;
      MoveTo(0, 0);
      LineTo(imgTest.Width, imgTest.Height);
    end;
  // Use the same transparent color as above, in this case yellow.
  DrawBitmapTransparent(imgTest.Picture.Bitmap.Canvas, 0, 0, Bmp, clYellow);
  imgTest.Invalidate;
  Bmp.Free;
end;

Regards,
JB
0
 

Author Comment

by:nifty
ID: 1356894
Thanks JB. As you can see I am fairly new at programming (but having a ball all the same)so expect to see postings from me often.I have bought several books and I understand them perfectly
after the 'problem' has been solved, isn't it always the same!
Once again thanks to all at expert exchange.....Nifty.
0

Featured Post

Tech or Treat! - Giveaway

Submit an article about your scariest tech experience—and the solution—and you’ll be automatically entered to win one of 4 fantastic tech gadgets.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This article explains how to create forms/units independent of other forms/units object names in a delphi project. Have you ever created a form for user input in a Delphi project and then had the need to have that same form in a other Delphi proj…
Creating an auto free TStringList The TStringList is a basic and frequently used object in Delphi. On many occasions, you may want to create a temporary list, process some items in the list and be done with the list. In such cases, you have to…
In this video, Percona Director of Solution Engineering Jon Tobin discusses the function and features of Percona Server for MongoDB. How Percona can help Percona can help you determine if Percona Server for MongoDB is the right solution for …
In response to a need for security and privacy, and to continue fostering an environment members can turn to for support, solutions, and education, Experts Exchange has created anonymous question capabilities. This new feature is available to our Pr…
Suggested Courses

636 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question