BitBlt Printer.Canvas to a TBitMap displays as solid white - delphi

Question

I am trying to capture Printer.Canvas as a Bitmap using BitBlt. I want to then take that Bitmap and display it on a paintbox. However, when I attempt this I am given only a white rectangle proportionate to the values I entered for Bitmap.SetSize. My printout looks correct, so I am almost positive the canvas of the printer is being properly drawn to. I attempted the following code using the variable bitmap as the destination and the paintbox as the source (in essence I was drawing a simple rectangle and line of text to the Paintbox, bitblt-ing it to a bitmap, clearing it, and then posting it back to the paintbox), but now that Printer.Canvas.Handle is the source it doesn't display.
I understand that the dimensions between the screen and printer are different so I will clearly indicate dimensions, just in case I am doing it wrong.
procedure TForm2.btnDrawClick(Sender: TObject);
begin
Printer.BeginDoc;
Printer.Canvas.Font.Size := 10; //Not Sure if this is necessary
Printer.Canvas.Font.Name := 'Arial'; //Not Sure if this is necessary
Printer.Canvas.Font.Color := clBlack; //Not Sure if this is necessary
Printer.Canvas.Rectangle(100,100,200,200); //Should print very tiny to paper
//But will look bigger when posted to
//The Paintbox
Printer.Canvas.TextOut(120,120,'XRay-Cat');
PCBitmap.SetSize(Paintbox1.Width,Paintbox1.Height); //Paint box is 300W,300H
Application.ProcessMessages;
BitBlt(PCBitmap.Canvas.Handle, //PCBitmap, is created on create, freed on destroy,
//Defined in the private section
0,
0,
PCBitmap.Width, //300
PCBitmap.Height, //300
Printer.Canvas.Handle,
0,
0,
SRCCOPY);
Application.ProcessMessages;
Printer.EndDoc;
procedure TForm2.btnPostBMClick(Sender: TObject);
begin
PaintBox1.Canvas.Draw(0,0,PCBitmap);
end;
I expect that the canvas would be written too, the canvas would be copied to a bitmap, then be available to be drawn on the paintbox. However all I see is a white rectangle. I am setting the dimensions of the bitmap to be the entire paintbox rather than the entire canvas of the printer. I am doing this because if I understand it correctly I should be only be drawing between the printer canvas's TopLeft 0,0 and BottomRight 300,300 the same way I would on my paint box. I would expect to see the same results as I would if I did this directly to the Paintbox.
Any help would be greatly appreciated. Thanks in advance.
Given the comments I've received it seems what I was trying to do was not possible. What I wanted to do was to write to a printers canvas and then get the image data of that canvas and store it in a bitmap. Since BitBlt can't be used is there a way to do what I wanted? I assume not, as I was told Printer.Canvas cannot be read from. At this point I have Found a way around it but I am just curious.

Answer 1

Switch your logic...draw to the PaintBox...and Print the PaintBox
procedure TForm55.Button1Click(Sender: TObject);
var
a_BM: TBitMap;
begin
a_BM := TBitmap.Create;
try
PaintBox1.Canvas.Font.Size := 10; //Not Sure if this is necessary
PaintBox1.Canvas.Font.Name := 'Arial'; //Not Sure if this is necessary
PaintBox1.Canvas.Font.Color := clBlack; //Not Sure if this is necessary
PaintBox1.Canvas.Rectangle(0,0,300,300); //Should print very tiny to paper
//But will look bigger when posted to
//The Paintbox
PaintBox1.Canvas.TextOut(120,120,'XRay-Cat');
PaintBox1.Width := 300;
PaintBox1.Height := 300;
a_BM.SetSize(PaintBox1.Width, PaintBox1.Height);
BitBlt(a_BM.Canvas.Handle, 0, 0, a_BM.Width, a_BM.Height, PaintBox1.Canvas.Handle, 0, 0, SRCCOPY);
Application.ProcessMessages;
Printer.BeginDoc;
Printer.Canvas.Draw(a_BM.Canvas.ClipRect.Left, a_BM.Canvas.ClipRect.Top, a_BM);
Printer.EndDoc;
Application.ProcessMessages;
finally
a_BM.Free;
end;
end;