Updating a Gauge and Detecting a User Interrupt (Delphi 6.0)

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.	Add 2 Button controls to your main form. Put them at the top of the form to keep them away from the image, name them as follows:
	Name	Caption
	btnMedian	Do Median
	btnQuit	Quit
3.	Add a TrackBar control to your main Form, and change the Max property of it to 100.
4.	On the Project pull-down menu, use the Import Type library… and select the LEAD Raster Process object library (14.5).
5.	Select LEAD Raster Process from the ActiveX tab and add it to your form.
6.	Add the Variables to the Private section of Unit1:

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

7.	Code the btnMedian Click’s procedure as follows:

procedure TForm1.btnMedianClick(Sender: TObject);
begin
    //Enable the ProgressStatus event
    LEADRasterProcess1.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
    LEADRasterProcess1.Median (LEADRasterView1.Raster, 4);
    //Clean up
    fInProc := False; //Processing is no longer taking place
    LEADRasterView1.ForceRepaint (  );
end;

8.	Handle the LEADRasterProcess1’s OnProgressStatus and code LEADRasterProcess1ProgressStatus as follows:

procedure TForm1.LEADRasterProcess1ProgressStatus(Sender: TObject;
  iPercent: Smallint);
begin
   Application.ProcessMessages (); //Detect Windows events
   if (not fEscape) then // Look for the Click on the Quit button
   begin
      TrackBar1.Position := iPercent;
   end
   else
      LEADRasterProcess1.EnableProgressEvent:= False; //Cancel the task
end;

9.	Code the btnQuit click’s procedure as follows:

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

10.	Handle the Form1 OnCloseQuery event, and code FormCloseQuery 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;

11.	Run your program to test it.