How NetRPG handles display files

[worksofliam]

I thought this might be an interesting thing to write about. For those that aren't aware, NetRPG is a .NET runtime (JIT) for free-format RPGLE applications. The latest thing that I have been working on is display file support.

This post does not indicate that display files are fully supported - because they are not and there is still a bit of work to do. The progress is good, though.

There are currently two steps to the runtime.

1. Parse into bytecode
2. Run bytecode in VM

Display files are interesting when it comes to the runtime because as of when this post is being written, the display file also gets parsed during runtime as well (when the display file is defined.)

Example display file

     A          R NEWFMT    
     A            NAME          20   O  7 46
     A            EMAIL         20   O  8 46
     A            ID            10D  B  5 46
     A                                      COLOR(WHT)
     A                                 20 25'F3=Exit'
     A                                      COLOR(BLU)
     A                                 20  9'Enter=Continue'
     A                                      COLOR(BLU)
     A                                  2 62SYSNAME
     A                                      COLOR(BLU)
     A                                  5 23'ID:'
     A                                  7 21'Name:'
     A                                  8 20'Email:'
     A                                  2 33'User Entry'
     A                                      COLOR(WHT)

This is a very simple display file. It has a single record format and three fields. It also has a lot of static text with colours and also the use of the SYSNAME keyword.

Compiling our program

Here is our RPG program:

Dcl-F ex3 WorkStn;

NAME = 'Barry';
EMAIL = '[email protected]';
exfmt NEWFMT;

Return;

When this program is executed under NetRPG, the compiler will open ex3 (our display file) and get all of the fields out of the record formats and put them into their respected data structures. For example, a structure called NEWFMT would be created with three subfields: NAME, EMAIL and ID. It does not care about the keywords of the display file fields at this point.

It would look something like this in RPGLE:

Dcl-Ds NEWFMT;
  NAME  Char(20);
  EMAIL Char(20);
  ID Zoned(10);
End-Ds;

This means we can then reference our three subfields in our program which is then used when the display file is rendered.

Executing the program

When the program is executed (e.g. it's executing the bytecode generated from the compiler) it will re-parse the display file again so the keywords can be used to format the display. NetRPG uses gui.cs under the covers to create a 'green screen' and NetRPG will create different Views for different types for fields.

Here is a snippet of code from the display renderer:

case FieldInfo.FieldType.Const:
    currentView = new Label (field.Value) { X = field.Position.X, Y = field.Position.Y };
    break;
    
case FieldInfo.FieldType.Output:
    currentView = new Label (Structure.GetData(field.Name).Get().ToString()) { X = field.Position.X, Y = field.Position.Y };
    break;

case FieldInfo.FieldType.Input:
    currentView = new TextField ("") {
        X = field.Position.X, Y = field.Position.Y,
        Width = field.dataType._Length,
        Height = 1
    };
    break;

Then after it's determined what type of field it is, it then handles the keywords (like SYSNAME or COLOR):

case "SYSNAME":
    (currentView as Label).Text = Environment.MachineName.Substring(0, Math.Min(8, Environment.MachineName.Length));
    break;

And the result is it creating display files: