Scrolling Canvas
Geoff
The only control I have found that allows this is a TForm, but that has
problems in that text can only be written to a visible section of the
screen.
Items derived from TGraphicControl have a canvas but cannot be scrolled.
TWinControls can be scrolled but do not have a canvas, or at least not a
visible one.
Q1) Do TWinContol components have a hidden canvass and if so how can
they be made visible?
I can create a TWinControl with a canvas, but when I try to write to
that canvas I get an error message "Canvas does not allow drawing" - (I
thought that was the purpose of a canvas!), and I can't get any further
at the moment.
Q2) How do I write to a canvas I have attached to a TWinControl
Q3) How do I get the canvas to paint, in particular at the correct
location.
Thanks in advance fore any assistance.
Geoff
Andrew Jameson
I'm maybe missing the point but it sounds too obvious to simply suggest that
you use a TMemo or TRichEdit that displays text and can scroll too ... so I
presume that you want to be able to write directly to a canvas in order to
maybe display other graphics / effects ... so why not put a TImage in a
TScrollBox ?
Andrew
Geoff <Ge...@nospam.com> wrote in message
news:3EA50F5A...@nospam.com...
Geoff
long scrollable region. By using the Scrollby method of a TWinControl I
can effectively achieve this because the canvas is just moved x pixels,
the displaced pixels are lost and new pixels are provided at the other
side.
Memos don't have a canvas so I can't write directly to them. If I use
an image it appears to have a finite size, and the scroll is of the
whole image component not just the canvas.
With a Form I can write to the canvas and progressively scroll the text,
adding more text as I progress. The only problem is that I can't write
to an invisible part of the form. I can't make the form bigger than the
screen anyway, and if I place another control over the spot where the
text is being written it simply does not appear when scrolled. If I
write even a single letter to the screen then this of course suddenly
appears and gives a non smooth appearance.
I could of course write the text to a separate canvas and then copy one
row of pixels at a time, but what I wanted to do was write to a piece of
canvas off screen and simply let it slide into view.
Geoff
Peter Below (TeamB)
> Thanks for the comments Andrew. My requirement is for an infinitely
> long scrollable region. By using the Scrollby method of a TWinControl I
> can effectively achieve this because the canvas is just moved x pixels,
> the displaced pixels are lost and new pixels are provided at the other
> side.
Use a TPaintbox to display the text, that is your canvas. You can plop it on a
panel, on the form itself, what best suits your need. You paint the text in the
paintboxes OnPaint event.
Here is an old example you may cannibalize.
<quote
source="http://codecentral.borland.com/codecentral/ccweb.exe/listing?id=19374">
Here is a bare-bones file viewer using a tstringlist for storage, a paintbox for
display, and a tscrollbar for navigation. It has no problems with a 4 MByte
file. (D4.03, Win95B)
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls, ComCtrls, Menus, ExtCtrls, Grids, ExtDlgs;
type
TForm1 = class(TForm)
Panel1: TPanel;
Panel2: TPanel;
ScrollBar1: TScrollBar;
Panel3: TPanel;
PaintBox1: TPaintBox;
Button1: TButton;
OpenDialog1: TOpenDialog;
Button2: TButton;
OpenPictureDialog1: TOpenPictureDialog;
procedure Button1Click(Sender: TObject);
procedure Panel3Resize(Sender: TObject);
procedure ScrollBar1Change(Sender: TObject);
procedure PaintBox1Paint(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
{ Private declarations }
FLines: TStringlist;
FLineHeight: Integer;
FTexture: TPicture;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
begin
If Opendialog1.execute then begin
if not assigned( FLines ) then
FLines := TStringlist.Create;
FLines.Loadfromfile( opendialog1.filename );
canvas.font.assign( paintbox1.font );
FLineheight := canvas.textheight( 'Äg' );
with scrollbar1 do begin
position := 0;
max := FLines.Count;
smallchange := 1;
panel3resize( nil );
end;
paintbox1.Invalidate;
end;
end;
procedure TForm1.Panel3Resize(Sender: TObject);
begin
If FLineHeight > 0 Then
with scrollbar1 do begin
LargeChange := paintbox1.Height div FLineheight - 1;
pagesize := largechange;
end;
end;
procedure TForm1.ScrollBar1Change(Sender: TObject);
begin
paintbox1.invalidate;
end;
procedure TForm1.PaintBox1Paint(Sender: TObject);
const
textcolors : array [0..3] of TColor =
(clBlack, clblue, clRed, clGreen);
var
n,x,y: Integer;
begin
with paintbox1, paintbox1.canvas do begin
if assigned( FTexture ) then begin
y:= 0;
while y < clientheight do begin
x:= 0;
while x < clientwidth do begin
draw( x, y, FTexture.Graphic );
Inc( x, FTexture.Width );
end;
Inc( y , FTexture.Height );
end;
end
else begin
brush.color := clWindow;
brush.style := bsSolid;
fillrect( clientrect );
end;
If not assigned( FLines ) Then
exit;
n:= scrollbar1.position;
y:= 0;
brush.Style := bsclear;
while (y < clientheight) and (n < Flines.count ) do begin
font.color := textcolors[ n mod 4 ];
textout( 2, y, Flines[n] );
inc( n );
inc( y, FLineHeight );
end;
end;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
with openpicturedialog1 do
if execute then begin
if not assigned( Ftexture ) then
FTexture := TPicture.Create;
Ftexture.loadfromfile( filename );
paintbox1.Invalidate;
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
paintbox1.parent.doublebuffered := true;
// required to avoid flicker
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
FTexture.free;
end;
end.
{
object Form1: TForm1
Left = 192
Top = 128
Width = 732
Height = 433
Caption = 'Form1'
Color = clBtnFace
Font.Charset = ANSI_CHARSET
Font.Color = clBlack
Font.Height = -17
Font.Name = 'Arial'
Font.Style = []
OldCreateOrder = False
OnCreate = FormCreate
OnDestroy = FormDestroy
PixelsPerInch = 120
TextHeight = 19
object Panel1: TPanel
Left = 0
Top = 0
Width = 588
Height = 406
Align = alClient
BevelInner = bvLowered
Caption = 'Panel1'
TabOrder = 0
object ScrollBar1: TScrollBar
Left = 568
Top = 2
Width = 18
Height = 402
Align = alRight
Kind = sbVertical
PageSize = 0
TabOrder = 0
OnChange = ScrollBar1Change
end
object Panel3: TPanel
Left = 2
Top = 2
Width = 566
Height = 402
Align = alClient
BevelOuter = bvNone
TabOrder = 1
OnResize = Panel3Resize
object PaintBox1: TPaintBox
Left = 0
Top = 0
Width = 566
Height = 402
Align = alClient
Color = clBtnFace
Font.Charset = ANSI_CHARSET
Font.Color = clBlack
Font.Height = -17
Font.Name = 'Times New Roman'
Font.Style = []
ParentColor = False
ParentFont = False
OnPaint = PaintBox1Paint
end
end
end
object Panel2: TPanel
Left = 588
Top = 0
Width = 136
Height = 406
Align = alRight
Caption = 'Panel2'
TabOrder = 1
object Button1: TButton
Left = 16
Top = 20
Width = 95
Height = 25
Caption = 'Open file'
TabOrder = 0
OnClick = Button1Click
end
object Button2: TButton
Left = 17
Top = 100
Width = 100
Height = 25
Caption = 'Texture'
TabOrder = 1
OnClick = Button2Click
end
end
object OpenDialog1: TOpenDialog
Filter = 'Textfiles (*.TXT)|*.TXT|Pascal source files|*.PAS;*.DPR'
Left = 608
Top = 56
end
object OpenPictureDialog1: TOpenPictureDialog
Filter =
'All (*.jpg;*.jpeg;*.bmp;*.ico;*.emf;*.wmf)|*.jpg;*.jpeg;*.bmp;*.' +
'ico;*.emf;*.wmf|JPEG Image File (*.jpg)|*.jpg|JPEG Image File (*' +
'.jpeg)|*.jpeg|Bitmaps (*.bmp)|*.bmp|Icons (*.ico)|*.ico|Enhanced' +
' Metafiles (*.emf)|*.emf|Metafiles (*.wmf)|*.wmf'
Left = 616
Top = 140
end
end
}
</quote>
--
Peter Below (TeamB)
Use the newsgroup archives :
http://www.mers.com/searchsite.html
http://www.tamaracka.com/search.htm
http://groups.google.com
http://www.prolix.be
Geoff
Geoff