Question :convert tpanel.canvas to bitmap when panel out of form
bounds?
lazarus / 39-Graphics

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Josh · 2017-11-20 19:55

Hope someone can help here.

5+ years ago I was playing around with panel canvas, ie copying a
panel canvas as a bitmap; that could then be used in another document
format.

As many image permutations and resolutions were being done, I thought
I had created the panel way off the forms boundary ( out of users
view).

Unfortunately I cannot find the code I used back then, but my memory
tells me that I just copied the tpanel canvas to a bitmap; when I try
this the area of the panel that is off the visible screen is blank.

If I move the panel into the visible area, then the visible part
becomes part of the tbitmap.

Has something changed, or is there another way to grab the contents of
a tpanel that is outside the screen bounds?

Code: [Select]var bmp:tbitmap;
begin
  bmp:=tbitmap.Create;
  bmp.Width:=panel1.Width;
  bmp.Height:=panel1.Height;
  panel1.Left:=-panel1.Width+trackbar1.Position;
  bmp.Canvas.CopyRect(rect(0,0,panel1.Width,panel1.Height),panel1.Canv
as,rect(0,0,panel1.Width,panel1.Height));
  image1.Picture.Bitmap:=bmp; // temp dump bmp to timage.
  bmp.Free;
end;


Trackbar used to bring panel in/out of focus of screen, image1 is a
timage that I drop the copied bmp onto to see what is happening.

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wp · 2017-11-20 21:36

This function
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
CreatePanelImage(APanel: TPanel): TBitmap;begin  Result :=
TBitmap.Create;  try    Result.SetSize(APanel.ClientWidth,
APanel.ClientHeight);    Result.Canvas.Brush.Color := clWhite;   
Result.Canvas.FillRect(0, 0, Result.Width, Result.Height);   
APanel.PaintTo(Result.Canvas, 0, 0);  except    Result.Free;   
raise;  end;end; seems to work even for an off-screen panel (at least
on Windows - did not test anything else). See attached demo

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Josh · 2017-11-20 23:45

Hi WP,

Thanks for your suggestion.

I have created a little test app using the function, but it still
shows an issue, if the panel has an image on it, this is not copied to
the tbitmap.

It copies the 2 controls I have placed on the form, but not the image.

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Josh · 2017-11-20 23:47

Pic, after transfer

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Josh · 2017-11-21 01:07

Hi

I created a procedure that does similar,
Not sure how cross-platform it is though.
Code: [Select]procedure GetControlAsBitmap(AControl
:TWinControl;ABitmap:TBitmap);
var
  DC: HDC;
begin
  // quick check to make sure control and bitmap are assigned.
  if not Assigned(ABitmap) then Exit;
  if not Assigned(AControl) then Exit;

  DC :=GetWindowDC(AControl.Handle);
  ABitmap.Width  :=AControl.Width;
  ABitmap.Height :=AControl.Height;
  BitBlt(ABitmap.canvas.Handle,0,0,ABitmap.Width,ABitmap.Height,dc,0,0
,SrcCopy);
  ReleaseDC(AControl.Handle, DC);
end;

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wp · 2017-11-21 09:37

Quote from: josh on November 21, 2017, 12:45:48 amHi WP,

Thanks for your suggestion.

I have created a little test app using the function, but it still
shows an issue, if the panel has an image on it, this is not copied to
the tbitmap.

It copies the 2 controls I have placed on the form, but not the image.
It does if the panel's ParentColor is off.