I am trying to duplicate the behaviour of PAINT application in Win 7 zoom track bar: (I know it's a common track bar control)
The 100% is located in the center. and it has 11 available positions:
etc...
12.5%, 25%, 50%, 100%, 200%, 300%, 400%, 500%, 600%, 700%, 800%
So my zoom values (ZoomArray
) are:0.125, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8
That's easy I could set Min to 1 and Max to 11 and get the values I need:ZoomArray[TrackBar1.Position]
The question is how to keep 100% in the center and the only positions that are available are the one above?
I have tried to use dummy values in the array to keep the 1 in the center e.g.:0.125, 0.25, 0.5, -1, -1, -1, -1, 1, 2, 3, 4, 5, 6, 7, 8
And reposition the trackbar on Change event, but my logic doesnt seem to work right.
Any ideas?
Here is one alternative that derives a new control from TTrackbar
, removing the automatic tics and handling sliding in the scroll message, behaves nearly identical to the control in Paint. Compiled with D2007, tried to comment a little:
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Controls, Forms, ComCtrls, StdCtrls;
type
TCNHScroll = TWMHScroll;
TTrackBar = class(comctrls.TTrackBar) // interposer class for quick test
protected
procedure CreateParams(var Params: TCreateParams); override;
procedure CreateWnd; override;
procedure CNHScroll(var Message: TCNHScroll); message CN_HSCROLL;
public
constructor Create(AOwner: TComponent); override;
end;
TForm1 = class(TForm)
Label1: TLabel;
TrackBar1: TTrackBar;
procedure TrackBar1Change(Sender: TObject);
end;
var
Form1: TForm1;
implementation
uses
commctrl;
{$R *.dfm}
procedure TForm1.TrackBar1Change(Sender: TObject);
begin
// account for non-linear scaling for a sensible value
if TrackBar1.Position <= 8 then
Label1.Caption := IntToStr(TrackBar1.Position * 125)
else
Label1.Caption := IntToStr(TrackBar1.Position * 1000 - 7000)
end;
{ TTrackBar }
constructor TTrackBar.Create(AOwner: TComponent);
begin
inherited;
// We'll have 15 positions which should account for the following values
// 125 250 - 500 - - - 1000 2000 3000 4000 5000 6000 7000 8000
// positions 3, 5..7 will be skipped when tracking
Min := 1;
Max := 15;
LineSize := 1;
PageSize := 1;
end;
procedure TTrackBar.CreateParams(var Params: TCreateParams);
begin
inherited;
// remove automatic ticks so that we don't have ticks at 3 and 5..7
Params.Style := Params.Style and not TBS_AUTOTICKS;
end;
procedure TTrackBar.CreateWnd;
begin
inherited;
// first and last tick not required
SetTick(2); // 250
SetTick(4); // 500
SetTick(8); // 1000
SetTick(9); // 2000
SetTick(10);
SetTick(11);
SetTick(12);
SetTick(13);
SetTick(14); // 7000
end;
procedure TTrackBar.CNHscroll(var Message: TCNHScroll);
var
Pos: Integer;
begin
// prevent jumping back and forth while thumb tracking, do not slide to the
// next tick until a threshold is passed
if Message.ScrollCode = SB_THUMBTRACK then begin
case Message.Pos of
5: SendMessage(Handle, TBM_SETPOS, 1, 4);
6, 7: SendMessage(Handle, TBM_SETPOS, 1, 8);
end;
end;
// for line and page and rest of the scrolling, skip certain ticks
Pos := SendMessage(Handle, TBM_GETPOS, 0, 0);
if Pos > Position then // compare with previous position
case Pos of
3: SendMessage(Handle, TBM_SETPOS, 1, 4);
5..7: SendMessage(Handle, TBM_SETPOS, 1, 8);
end;
if Pos < Position then
case Pos of
3: SendMessage(Handle, TBM_SETPOS, 1, 2);
5..7: SendMessage(Handle, TBM_SETPOS, 1, 4);
end;
inherited;
end;
end.
Vertical implementation would be similar, if needed. This is not really a finished product, just a trial to mimic the behavior of the mentioned control.
Set TrackBar.Max
to 14
, and implement the OnChange
and OnKeyDown
handlers, as well as maybe some button OnClick handlers for zooming in and out. Also, set TrackBar.PageSize = 4
to get the PageUp and PageDown keys correctly working.
const
ZoomTickCount = 15;
function ZoomLevelPos(Position: Integer; GoneUp: Boolean): Integer;
const
Ticks: array[0..ZoomTickCount - 1] of Integer =
(0, 1, 1, 2, 2, 2, 2, 9, 10, 11, 12, 13, 14, 15, 16);
begin
Result := Position;
if GoneUp then
while (Result < High(Ticks)) and (Ticks[Result] = Ticks[Position - 1]) do
Inc(Result)
else
while (Result > Low(Ticks)) and (Ticks[Result - 1] = Ticks[Position]) do
Dec(Result);
end;
procedure TForm1.ZoomTrackBarChange(Sender: TObject);
const
Zooms: array[0..ZoomTickCount - 1] of Single =
(0.125, 0.25, 0.25, 0.5, 0.5, 0.5, 0.5, 1, 2, 3, 4, 5, 6, 7, 8);
begin
ZoomTrackBar.Position := ZoomLevelPos(ZoomTrackBar.Position, False);
Label1.Caption := Format('%.1n%%', [Zooms[ZoomTrackBar.Position] * 100]);
end;
procedure TForm1.ZoomTrackBarKeyDown(Sender: TObject; var Key: Word;
Shift: TShiftState);
begin
if Key in [VK_DOWN, VK_RIGHT] then
begin
ZoomTrackBar.Position := ZoomLevelPos(ZoomTrackBar.Position + 1, True);
Key := 0;
end;
end;
procedure TForm1.ZoomInButtonClick(Sender: TObject);
begin
ZoomTrackBar.Position := ZoomLevelPos(ZoomTrackBar.Position + 1, True);
end;
procedure TForm1.ZoomOutButtonClick(Sender: TObject);
begin
ZoomTrackBar.Position := ZoomTrackBar.Position - 1;
end;
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