/*
When you do custom drawing, such as shown in the code for
the Button's OnClick event handler below, this drawing will
not be persistent and will be "erased" the first time the
PaintBox component needs to repaint.
*/
void __fastcall TForm1::Button1Click(TObject *Sender)
{
   PaintBox1->Canvas->Brush->Color = clRed;
   PaintBox1->Canvas->FillRect(PaintBox1->Canvas->ClipRect);
   PaintBox1->Canvas->Ellipse(0,0,100,100);
}

/*
In order for the drawing to be persistent, you need to also
include an OnPaint event handler that tells the PaintBox how
to redraw itself when it needs to. In the code below, an
ellipse will be drawn everytime the PaintBox renders itself,
but the PaintBox will only paint the client area of the
control red after the Button is clicked. This client area
will only stay red until it is invalidated, but the ellipse
will persist. This behavior is different from the TImage
component, because the TImage component maintains an
internal bitmap that stores this drawing information for
you.
*/
void __fastcall TForm1::PaintBox1Paint(TObject *Sender)
{
   PaintBox1->Canvas->Brush->Color = clBlue;
   PaintBox1->Canvas->Ellipse(0,0,100,100);
}

/*
The following code uses ClientRect to find and draw a line
from the top left to the bottom right of the current
control.  Select a TControl in the ListBox list.  This
example assumes that the current object is a descendent of
TControl and has a public Canvas property.
*/
{
  TPoint APoint = Point(X, Y);
  int Index = ListBox1->ItemAtPos(APoint, True);
  TLabel *myLabel;
  TClass ClassRef = ListBox1->Items->Objects[Index]->ClassType();
  if (String(ClassRef->ClassName()) == "TLabel")
  {
    myLabel = dynamic_cast<TLabel *>(ListBox1->Items->Objects[Index]);
    // make sure we are using the TControls canvas and not the from's!
    myLabel->Canvas->MoveTo(myLabel->ClientRect.Left, myLabel->ClientRect.Top);
    myLabel->Canvas->LineTo(myLabel->ClientRect.Right, myLabel->ClientRect.Bottom);
    myLabel = NULL;
  }
}

/*
The following code draws the graphic in Picture1 in the
top-left corner PaintBox1.  Place a TPaintBox in the form 
and a TImage in the form that contains a picture.
*/
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  PaintBox1->Canvas->Draw(0,0, Image1->Picture->Graphic);
}

{
When you do custom drawing, such as shown in the code for
the Button's OnClick event handler below, this drawing will
not be persistent and will be "erased" the first time the
PaintBox component needs to repaint.
}
procedure TForm1.Button1Click(Sender: TObject);
begin
   PaintBox1.Canvas.Brush.Color := clRed;
   PaintBox1.Canvas.FillRect(PaintBox1.Canvas.ClipRect);
   PaintBox1.Canvas.Brush.Color := clBlue;
   PaintBox1.Canvas.Ellipse(0,0,100,50);
end;
{
In order for the drawing to be persistent, you need to also
include an OnPaint event handler that tells the PaintBox how
to redraw itself when it needs to. In the code below, an
ellipse will be drawn everytime the PaintBox renders itself,
but the PaintBox will only paint the client area of the
control red after the Button is clicked. This client area
will only stay red until it is invalidated, but the ellipse
will persist. This behavior is different from the TImage
component, because the TImage component maintains an
internal bitmap that stores this drawing information for
you.
}
procedure TForm1.PaintBox1Paint(Sender: TObject);
begin
   PaintBox1.Canvas.Brush.Color := clBlue;
   PaintBox1.Canvas.Ellipse(0,0,100,50);
end;

{
The following code uses ClientRect to find and draw a line
from the top left to the bottom right of the current
control.  Select a TControl in the ListBox list.  This
example assumes that the current object is a descendent of
TControl and has a public Canvas property.
}
  if (ListBox1.Items.Objects[Index] is TLabel) then
  begin
    myLabel:= (ListBox1.Items.Objects[Index] as TLabel);
    with myLabel.ClientRect do
    begin // make sure we are using the TControl's canvas and not the form's!
      myLabel.Canvas.MoveTo(Left, Top);
      myLabel.Canvas.LineTo(Right, Bottom);
    end;
  myLabel:= nil;
  end;

{
The following code draws the graphic in Picture1 in the
top-left corner PaintBox1.  Place a TPaintBox in the form 
and a TImage in the form that contains a picture.
}
procedure TForm1.Button1Click(Sender: TObject);
begin
  PaintBox1.Canvas.Draw(0,0, Image1.Picture.Graphic);
end;