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VAGUE  April 2005

VAGUE April 2005

Subject:

Re: POS

From:

Rion D'Luz <[log in to unmask]>

Reply-To:

Vermont Area Group of Unix Enthusiasts <[log in to unmask]>

Date:

Sat, 23 Apr 2005 17:18:08 -0400

Content-Type:

Multipart/Mixed

Parts/Attachments:

Parts/Attachments

Text/Plain (100 lines) , gnupos.tgz (100 lines)

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Hash: SHA1

from the gnuPOS README

Last updated: 04-JULY-2001

I have started development of a point-of-sale program. I'll spare you the long story, but suffice to say that I've used QuickPOS (the point-of-sale offering from Intuit/Quicken) and its got holes you can drive trucks through. Having been inspired by Gnucash, I decided the best solution was to write a GPL'd equivalent.

I'll update this as I go along, but don't expect it to be immensely current!

WHAT I WANT
Well, everything, really. In unordered point-form:
- - interface to gnucash ('cos that is where my accounts are).
- - stand-alone capability (just in case some strange people don't want to run gnucash).
- - configurable gui ('cos not everyone wants things looking the same).
- - programmable keymap/other input structure (so it can be used in a whole stack of different industries).
- - stock-control/inventory stuff. 
- - multi-user/multi-instance operability with *SECURITY* a high priority
- - credit-card processing (in the future).
- - interface to online-processing systems.
- - no doubt many more things that just don't come to mind at the moment.

WHAT I'VE DONE SO FAR
This is open to comments - I want feedback before I progress too far to make changing practical.
- - The gui exists in rather unpolished form. The layout look remarkably similar to the QuickPOS layout. Essentially, it consists of a long, narrow text box at the top to contain the "current input". The rest of the window below that is divided into two panes, the left to contain on ongoing log similar to the paper cash-register rolls the average cash register produces (this should probably also log to a file). The right-side pane is intended as a help/prompt/message window. The stuff output to either will be programmable.
- - Most of the functionality to resize works mostly ok for what I've done, but it needs cleaning up. There are no doubt other options I've not considered that could be added.
- - I have writen some basic functions for displaying stuff in the gui, but it was primallily intended for testing purposes, and will no doubt need to be extended. In particular, I'm eagerly awaiting GTK+ 2.0, which has some much nicer text display widgets that I'd like for the right pane in particular. This stuff (to the extent that it is used) does work fine.
- - After a (miniscule) amount of discussion on irc and with friends, I have decided an xml-format file is the go for keyboard programming, using a state machine setup. I'm not sure how to explain this, so just throw ideas at me, and I'll add/change stuff that seems interesting. It is my intention that *all* operation go through the state machine (in other words, I want no "automatic" things that happen - everything should happen or not happen according to the programming). This stuff desperately needs to be documented and extended beyond the fairly basic stuff I've done. Ideas?
- - I have writen the some pretty basic stuff for reading the xml file and building the state tables. This stuff works but does minimal or no error checking, which can lead to some frustrating problems when things don't appear to be working, but you really have a bug in the state program.
- - The keystroke processing stuff is present and appears to work, but again does minimal to no error checking. It mostly consists of a number of arrays containing the necessary data as fed in on the reading of the xml file. It is my hope that this will be quick without being too much of a memory hog, but this may have to be revisited again in the future once some experience is gained. Feel free to throw suggestions at me. 
- - It is my intention (once I get that far) to have all numerical values treated as gnc-numerics. One of my really huge gripes about QuickPOS is that it uses low-bitcount floats for price representations, leading to rounding errors in some cases for multiples as low as 2. This is completely avoidable and utterly wrong in my opinion, so mine will not do that.

OTHER ISSUES
Not much to add here at the moment, except that:
- - ultimately, some way is going to have to be found to encrypt the data. Of course, we don't have any data that really needs encrypting just at the moment (I don't think encrypting the keyboard program xml file is really necessary). This is a multi-user issue (and potentially an issue when inventory stuff is added).
- - There is a TO-DO file that will contain the more obvious ommissions. I suggest you read it!

HOW IT WORKS
This could potentially become quite a lengthy section, particularly the bit about programming the state machine.

You must always remember that there are 2 stages to the "execution" of the state machine:
- - Loading the definitions from the xml file;
- - and, then subsequently executing them when certain keys are pressed when in the required state.

The tables, and their functions are:
* Keysym Table
This table ONLY exists for load time. It is not used during run time. It contains a lookup-table to convert various symbolic names for keys (or a few special key groups) into a numeric representation. This numeric representation will (if I'm lucky) always correspond to the appropriate keys as pressed on the keyboard. In other words, the ascii values for the keys are returned to the program when a normal key is hit, and the table should contain that ascii value for the representation of the key (for example 'c' should have a code value of 0x43). The code value is stored in the state table (see below) and used for comparison to see if that key has been hit to trigger that section.

* State Table:
This table is used for both load and run time. During load time, it is filled with the name, the various inputs responded to in that state, and the actions to take for those inputs. It also contains a field with the current state, and a count of the number of states in the table.
When a key is hit, we search the valid inputs for the current state to see what action (if any) should be taken on that key press. If a valid input match is found, we perform the commands as directed by that input section, and then execute the change of state as directed by that section. Commands are contained in a linked list structure pointed to by the input section. Further details are contained in the Functions Table (see below).

* Register table
This table is also used at both load and run time. It contains the definition for all registers (both internal and program) used by the state machine in its execution. Special registers are flagged as such and inserted into the table before any other registers are loaded, which prevents state programs from using those names. These will be documented elsewhere at some later stage. A number of special and internal registers exist. In particular:
  -  A special register exists for each display field on the screen to permit the state programs to access and change these fields.
  -  A number of special registers exist for particular things (like the current key pressed).
  -  A couple of special registers exist for passing constants entered into the state program to commands.

*  Functions table
Similarly, this exists at both load and run time. It contains the instructions contained in the state program, converted into an internal representation that can be "executed" on the appropriate trigger input. All internal commands are contained in this table, as are all state program defined functions.


Conrad.


On Saturday 23 April 2005 00:59, you wrote:
> Anyone have a lead on free point of sale software for linux?
>
> Distro isn't really so important, though preferably one that a total
> newb can be taught to feel comfortable using.
>
> Chris
> --
>    c  h  r  i  s  .  m  o  r  a  n  @  g  m  a  i  l  .  c  o  m
> b  u  t   y  o  u    k  n  o  w    t  h  a  t    a  l  r  e  a  d  y

- -- 
                                     3010 Rte 109
                                     Waterville, VT 05492
                                     email: riondluz_at_starband.net
                                     web: http://dluz.tzo.com:8080/Rion/
                                     Phone: 802.644.2255

                 L I N U X       .~.
                  Choice         /V\
                 of a  GNU      /( )\
                Generation      ^^-^^
                                POSIX
                                RULES

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