Updating a Gauge and Detecting a User Interrupt (Delphi 4.0)

Take the following steps to update a gauge during processing and detect a user interrupt:

1.	Start with the project that you created in Loading and Displaying an Image.
2.	$image\btncmd.gif$ Add 2 Button controls to your main form. Put them at the top of the form to keep it away from the image, name them as follows:
	Name	Caption
	Button1	Do Median
	Button2	Quit
3.	Add a TrackBar control to your main Form, and change the Max property of it to 100.
4.	If you didn’t install LEvntSnk, install it.
	On the Component pull-down menu, use install component …, and browse to LEADXX\Include\LEvntSnk.pas, and press Ok.
5.	From the ActiveX controls, Add the LEvntSnk control to your form.
6.	Add the Variables to the Private section of Form1:

fEscape: Boolean; //Use to indicate the user interrupt
fInProc: Boolean; //Use to avoid closing the form during processing
RasterProc: LEADRasterProcess;

7.	Now, add the following to the Form's Create event to create the ILEADRasterProcess object

// Create the Rasterproc object.
RasterProc:= CreateComObject (CLASS_LEADRasterProcess) as LEADRasterProcess;
LEADEventSink1.Connect (RasterProc, _LEADRasterProcessEvents);

8.	Code the Button1 Click’s procedure as follows:

procedure TForm1.Button1Click(Sender: TObject);
var
   sRet: Smallint;
begin
    //Enable the ProgressStatus event
    RasterProc.EnableProgressEvent:= True;
    //Initialize the indicators
    fEscape := False; //The user does not want to quit
    fInProc := True; //Processing is taking place
    //Perform a relatively slow median filter
    RasterProc.Median (LEADRasterView1.Raster, 4);
    //Clean up
    fInProc := False; //Processing is no longer taking place
    LEADRasterView1.ForceRepaint (sRet);
end;

9.	Code the LEADEventSink1 OnInvoke event as follows:

   procedure TForm1. LEADEventSink1Invoke(Sender: TObject; DispID: Integer;
  const IID: TGUID; LocaleID: Integer; Flags: Word; Params: tagDISPPARAMS;
  varResult, ExcepInfo, ArgErr: Pointer);
var
   iPrecent: OleVariant;
begin
   iPrecent:= OleVariant(Params.rgvarg^[0]);
   case (DispID) of
      LEADRASTERPROCESSEVENTS_PROGRESSSTATUS:
      begin
          Application.ProcessMessages (); //Detect Windows events
          if (not fEscape) then // Look for the Click on the Quit button
         begin
            TrackBar1.Position := iPrecent;
         end
          else
            RasterProc.EnableProgressEvent:= False; //Cancel the task
      end;
   end;
end;

10.	Code the Button2 click’s procedure as follows:

procedure TForm1.Button2Click(Sender: TObject);
begin
fEscape:= True; //The user wants to quit
Trackbar1.Position := 0 ;
end;

11.	Code the Form1 CloseQuery procedure as follows:

procedure TForm1.FormCloseQuery(Sender: TObject; var CanClose: Boolean);
begin
if (fInProc) then //If processing is taking place
CanClose:= False; //Do not let the user close the form
end;

12.	On the Project pull-down menu, use the Import Type library… and select the LEAD Raster Process object library (14.5).
13.	At the beginning of the Unit1 file, add LTRASTERPROCLib_TLB to the uses section. For example:

Uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, LTRASTERPROCLib_TLB;

14.	Run your program to test it.