// Draws the specified bitmap onto another bitmap,
// if bTransparent is true then the bottom left pixel are used to determine the
// transparecny color
procedure DrawBitmapOntoImage(SourceBMP: TBitmap; // the bitmap to draw
                              DestCanvas: TCanvas;                  // the Canvas to draw onto
                              DestCanvasWidth: Integer;             // The width of the canvas we are drawing on
                              DestCanvasHeight: Integer;            // The Height of the canvas we are drawing on
                              iLeft: Integer;
                              iTop: Integer;                        // the position to draw SourceBMP
                              bTransparent: boolean); // if true then all pixels of the same color as the the bottom left pixel are drawn as transparen
var
  TempBMP : TBitmap;
  rctObject : Trect;
begin
  tempbmp := TBitmap.create;
  try
    RctObject := rect(iLeft,
                      iTop,
                      iLeft + SourceBMP.width,
                      iTop + SourceBMP.Height);

    // check that it doesn't extend beyond the end of the image
    if RctObject.right > DestCanvasWidth then
      RctObject.right := DestCanvasWidth;
    if RctObject.bottom > DestCanvasHeight then
      RctObject.bottom := DestCanvasHeight;

    TempBMP.width  := RctObject.right - RctObject.left;
    TempBMP.height := RctObject.bottom - RctObject.top;

    TempBMP.canvas.copymode := cmsrcCopy;
    TempBMP.canvas.copyrect(rect(0, 0, TempBMP.width, TempBMP.height), DestCanvas, RctObject);

    SourceBMP.width := RctObject.right - RctObject.left;
    SourceBMP.height := RctObject.bottom - RctObject.top;

    SourceBMP.transparent := bTransparent;

    TempBMP.canvas.Draw(0, 0, SourceBMP);

    if (bTransparent = false) then
      DestCanvas.copyrect(RctObject, SourceBMP.canvas, rect(0, 0, SourceBMP.width, SourceBMP.height))
    else
      DestCanvas.copyrect(RctObject, TempBMP.canvas, rect(0, 0, TempBMP.width, TempBMP.height));
  finally
    tempbmp.free;
  end;
end;