VX/DECFORMS: Seamless Migration of DECforms from VMS/OpenVMS to Linux and Windows
VX/DECForms offers a comprehensive implementation of DEC’s OpenVMS DECforms. This solution delivers an exact emulation of DECforms, ensuring that form management and functionality are preserved across platforms. VX/DECFORMS is a library of FORMS$ APIs, mirroring the original DECForms API and maintaining compatibility with OpenVMS systems.
The system compiles IFDL (Interactive Forms Definition Language) into a C++ logic subroutine that mirrors the flow of the original IFDL, with verbs converted into C++ classes. These C++ classes retain the same names and attributes as the original IFDL, ensuring consistency in functionality. The generated C++ code emits ANSI escape codes just like DECforms, providing a 100% functional emulation, where users cannot distinguish between the migrated screen and the original OpenVMS DECforms.
While VX/DECFORMS supports nearly all DECforms syntax, it currently does not support right-to-left text formatting. The platform also allows the display of DECforms in modern HTML5 browsers, broadening access to legacy applications.
Key Features of VX/DECFORMS
• Complete Feature Set: VX/DECFORMS retains all features of the original OpenVMS DECforms system, including scrolled areas, named data, overlapping forms, and more.
• Full Terminal Support: It is compatible with all VT terminals (VT100 and higher), including DECterm in DECwindows, ensuring broad device support.
• Double-Width & Double-Height Characters: Supports advanced display options, such as 132-character mode, help forms, and user-defined routines (UARs).
• Emulation of Original DECforms: Focused on a 100% functional migration, VX/DECForms preserves the complex attributes and functionality of DECforms without enhancing or altering the core features.
• Seamless Integration with VX/RT: For applications requiring full integration with VMS, VX/DECFORMS works seamlessly with VX/RT, Sector7’s runtime support libraries for Linux.
Introduction to VX/DECFORMS
Originally designed for VMS systems, DECforms posed significant challenges for migration due to its complexity, VMS-specific dependencies, and platform-specific programming constructs. Until now, migrating DECforms-based applications to modern platforms has been impractical. VX/DECFORMS eliminates these barriers by offering a comprehensive set of language interface utilities, enabling the migration of DECforms-created forms to Linux environments.
The VX/DECFORMS utilities support multiple programming languages, including Fortran, C, COBOL, and VX/BASIC, and provide the necessary procedures to adapt VMS descriptors and facilitate integration with modern platforms. These system-independent routines enable smooth linking and transition to new environments.
Functionality of VX/DECFORMS
VX/DECFORMS enables developers to leverage many advanced features of DEC’s VT family, such as:
• Character Attributes: Including reverse video, bold, blinking, and underlined text.
• Line Attributes: Such as double-width and double-height characters, as well as scrolled lines.
• Screen-Width Attributes: Supporting both 80-column and 132-column modes, as well as reverse video.
• Alternative Character Sets: Full support for VT100 special graphics and line-drawing characters.
The VX/DECFORMS compiler translates ASCII-form descriptions (FLEX files) into an internal binary format, which is then used to display forms and validate user input at runtime. The migration process does not require changes to application programs; once the form descriptions are updated, the application automatically utilizes the new forms through the runtime system.
Form Driver: The Heart of VX/DECFORMS
The Form Driver is the runtime component of VX/DECFORMS responsible for handling terminal input and output, displaying forms, managing screen manipulation, and performing basic input validation. It supports:
• Field-based and Full-form Input/Output: Allows specification of inputs one field at a time or across the entire form.
• Efficient Terminal Drivers: Built-in C-based terminal drivers provide portability across Linux/Windows platforms without relying on external tools like curses or termcap.
• Terminal Compatibility: Fully supports VT100 and higher terminals, including DECterm under DECwindows, and can be extended for non-VTxxx terminals as needed.
This eliminates the need for external terminal configuration files, ensuring high portability and ease of deployment across diverse environments.
User Escapes (PUEs): Custom User Procedures
User Escapes (PUEs) are custom routines written by users in any DEC-supported programming language. These procedures are tied to forms and fields during the creation of form data structures and are triggered automatically by the Form Driver in several scenarios:
• After field processing.
• Before and after help requests.
• When function keys are pressed.
• During screen refresh operations.
PUEs in VX/DECFORMS behave identically to those in the original OpenVMS DECForms, with added flexibility. The IFDL compiler converts the IFDL into maintainable C++ code, allowing for direct linking of external routines into the compiled IFDL, giving you greater control and flexibility over form interactions.
IFDL Forms Compiler: Simplifying the Form Definition Process
IFDL (Interactive Forms Definition Language) is a declarative, keyword-oriented language used to create and modify form source descriptions. The VX/DECFORMS compiler translates these IFDL files into C++ subroutines used at runtime. The system links DECforms Call Outs normally, adhering to standard scoping rules.
This robust compiler allows developers to create, modify, and compile forms efficiently, supporting a modern development environment while preserving the legacy functionality of DECForms.
With VX/DECFORMS, migrating legacy DECforms applications to Linux and Windows has never been easier. Our solution provides a seamless experience that preserves the original functionality, allowing your forms to continue running efficiently and effectively in modern environments.
