In addition, the TCanvas represents a fairly complete wrapper around the graphics API of Windows so there are methods to support functionality that would otherwise require the use of the Windows API in VB. Examples are: CopyRect, FloodFill, and Polygon. The key portion of VBSAMPLESCALLDLLSCALLDLLS.MAK code in VB looks like this:

temp = BitBlt(hDC, X, Y, PicWidth, PicHeight, picCopy.hDC, 0, 0, SRCCOPY)

temp = BitBlt(picCopy.hDC, 0, 0, PicWidth, PicHeight, hDC, NewX, NewY, SRCCOPY)

temp = BitBlt(hDC, NewX, NewY, PicWidth, PicHeight, picMask.hDC, 0, 0, SRCAND)

temp = BitBlt(hDC, NewX, NewY, PicWidth, PicHeight, picSprite.hDC, 0, 0, SRCINVERT)

the same functionality in the Delphi example looks like this:

C.CopyMode := cmSrcAnd;

C.CopyRect (Dest, imgMask.Canvas, Src);

C.CopyMode := cmSrcInvert;

C.CopyRect (Dest, imgSprite.Canvas, Src);

C.CopyMode := cmSrcCopy;

where C refers to the canvas property of an image control. Furthermore, it is possible to create a canvas and assign an hDC into that canvas, thereby minimizing the amount of Windows API functionality required. In the Sprite sample, the code checks whether to act on the form or the desktop and assigns a different value to the local canvas variable:

if chkDesk.State = cbChecked then begin

C := TCanvas.Create;

C.Handle := GetDC(GetDesktopWindow);

RightEdge := GetSystemMetrics(SM_CXSCREEN);

BottomEdge := GetSystemMetrics(SM_CYSCREEN);

end

else begin

C := Canvas; {the Canvas property of the form}

RightEdge := ClientWidth;

BottomEdge := ClientHeight;

end;

Therefore, the canvas is an extremely important aspect of graphics programming in Delphi, especially from the perspective of hiding the complexity of manipulating the drawing surface of different objects.