** 1 page regular / 878 words **

Basic BASIC!

One of the computing laws of programming is Stockmayer's Theorem. 
It states "If it looks easy, it's tough - if it looks tough, it's 
damn near impossible". Stockmayer obviously didn't have HBASIC 
when he wrote his statement...

Over the past few months I've shown you some of the basic 
functions of HBASIC. We can now continue with our PDO program 
adding much more features. This issue we'll concentrate on:

** UL **
* Adding the file selector for the print/view option.
* Creating a Program Options dialog with the ability to specify a 
viewing program.
* Checking for a command line and automatically going to the print 
command straight away.
** /UL **

To leave more space for an in-depth explanation the source code 
listing is only included on the Reader Disk this issue.

The File Selector

The file selector has been one of the nicest features of the Atari 
platform since the first TOS v1.0 machines sold in 1985 and it's 
one of the most useful programming tools and is fully accessible 
using HBASIC. The function comes in two versions, one for AES 
versions 1.62 or earlier (below TOS 1.4) and another one for later 
AES versions.

Although the layout of the file selector has changed slightly over 
the years as extra refinements have been added the pre-AES call 
only differs in one way, it doesn't include a prompt "message" 
such as "Please select file to use" and so on.

** FSEL.GIF here **

I've included three extra subs/functions in the PDO source which 
are:
SUB aes_version, SUB InitFileSelector and FUNCTION fileselector$. 
Both sub routines are used by the file selector function:

** UL **
* aes_version returns your AES version
* InitFileSelector sets internal settings for the main file 
selector function.
** /UL **

The selector routine takes in one parameter, which is the message 
that is to be displayed. The routine first checks if the starting 
path has been defined (which is what InitFileSelector does) and 
then decides on which call to make, depending on your version of 
the AES. The variable fspath$ after the call is the last path of 
the program, which the extension of the search field as well. The 
loop is needed to get rid of this so the path and name (returned 
in fsname$) can be returned by the function.

How can this be used? Well, if you find the ProcessUserMenus 
section and find "CASE view", you'll see I've used this function 
to get the user to select the file they wish to view. If the user 
clicks on Cancel, the function will return a null string, so this 
is also checked. Another feature we'll look at more closely next 
issue is the execution (running) of the external viewer (the 
"execute" statement). The same thing has also been done in the 
print file section.

The Program Options form

** PROGOPTS.GIF here **

The code has been inserted as "CASE progopts". The first thing we 
do is to get the string for the external viewer in temp_1$ so that 
if the user clicks on Cancel, we can replace the stated address 
with the old temporary version. The program then goes into a loop, 
so that no matter what button the user presses, the form will 
never close until either the OK or Cancel button has been pressed. 
If the Cancel button is pressed, the file viewer disk address is 
changed back to what is was. If the Change viewer button was 
selected, another file selector is displayed - useful eh?

When the routine actually finishes, there is a "global" (shared) 
variable named global_viewer$ which contains the name of the 
viewer which is used when the view file option is called on. 
Please note that the keyboard shortcut has also been added to SUB 
do_keybd.

The Command line

Remember in AC#12 we introduced the COMMAND$ command? Well, we're 
going to use it now - there's going to be automatic print option 
when double-clicking on a printable file (assuming it's had it's 
file type registered with the program).

When the program first loads, the prinfile$ variable is set to the 
command line. If this is null the program will simply ignore it, 
otherwise the variable commandline is set to 1, and the print 
option is ran. In the print option, if the commandline variable is 
set 0 (which means a command line wasn't used) the program 
automatically asks the user for the file to be printed. In this 
case, if a file has been double-clicked on, the program is 
executed and the file printed straight away without having to 
select the file again.

In the next few remaining issues, I shall be covering:

** UL **
* The execute routine, including the option for the VA protocol 
(below)
* Using the VA protocol to call the external viewer. That is, in a 
multitasking system, if the program and the external viewer is 
being executed, both programs can communicate with each other.
* The Registration validation (including exclusive version of the 
latest validation routines from ENCHANT) - including generating a 
real registration key using the check digit idea in AC#12.
* Using ENCHANT. A full guide to each of the benefits of the using 
the system, including window dialogs, ST Guide help, BubbleGEM 
help, popup menus, check boxes etc.
* Insights into the Virtual Language project.
** /UL **

Email: paul.jones31@virgin.net
http://vzone.virgin.net/paul.jones31/