DVX -- DOS Visual eXecutive

A windowed GUI compositor and widget toolkit targeting DJGPP/DPMI on 486+ hardware. VESA VBE 2.0+ LFB only. Motif-inspired visual style with 2px bevels, fixed bitmap fonts, and dirty-rect compositing.

The system runs on 86Box (primary target) and real DOS hardware.

Architecture

DVX is built as a set of DXE3 dynamic modules loaded by a bootstrap executable. The loader resolves dependencies and loads modules in topological order, then hands control to the shell.

dvx.exe (loader)
  |
  +-- libs/libtasks.lib      cooperative task switcher
  +-- libs/libdvx.lib        core GUI (draw, comp, wm, app, widget infra)
  +-- libs/texthelp.lib      shared text editing helpers
  +-- libs/listhelp.lib      shared list/dropdown helpers
  +-- libs/dvxshell.lib      shell (app lifecycle, desktop)
  +-- libs/taskmgr.lib       task manager (Ctrl+Esc, separate DXE)
  |
  +-- widgets/*.wgt           26 widget type plugins
  |
  +-- apps/*/*.app             DXE applications

Directory Structure

Directory	Output	Description
loader/	bin/dvx.exe	Bootstrap loader, platform layer, stb_ds
core/	bin/libs/libdvx.lib	Core GUI library (5 layers + widget infra)
tasks/	bin/libs/libtasks.lib	Cooperative task switching
texthelp/	bin/libs/texthelp.lib	Shared text editing helpers
listhelp/	bin/libs/listhelp.lib	Shared list/dropdown helpers
shell/	bin/libs/dvxshell.lib	DVX Shell (app lifecycle, desktop)
taskmgr/	bin/libs/taskmgr.lib	Task Manager (separate DXE, Ctrl+Esc)
widgets/	bin/widgets/*.wgt	26 individual widget DXE modules
apps/	bin/apps/*/*.app	Application DXE modules
tools/	bin/dvxres	Resource tool (host native, not DXE)
config/	bin/config/, bin/libs/, bin/widgets/	INI config, themes, wallpapers, dep files
rs232/	lib/librs232.a	ISR-driven UART serial driver
packet/	lib/libpacket.a	HDLC framing, CRC-16, Go-Back-N ARQ
security/	lib/libsecurity.a	DH key exchange, XTEA-CTR cipher, RNG
seclink/	lib/libseclink.a	Secure serial link (channels, encryption)
proxy/	bin/secproxy	Linux proxy: 86Box <-> telnet BBS
termdemo/	bin/termdemo.exe	Standalone encrypted terminal demo

Build

Requires the DJGPP cross-compiler at ~/djgpp/djgpp.

make              # build everything
make clean        # remove all build artifacts
./mkcd.sh         # build + create ISO for 86Box

The top-level Makefile builds in dependency order:

core -> tasks -> loader -> texthelp -> listhelp -> widgets -> shell -> taskmgr -> apps
                                                                                  tools (host native, parallel)

Build output goes to bin/ (executables, DXE modules, config) and obj/ (intermediate object files).

Runtime Directory Layout (bin/)

bin/
  dvx.exe                   bootstrap loader (entry point)
  libs/
    libtasks.lib             task switching library
    libdvx.lib               core GUI library
    texthelp.lib             text editing helpers
    listhelp.lib             list/dropdown helpers
    dvxshell.lib             DVX shell
    taskmgr.lib              task manager (Ctrl+Esc)
    *.dep                    dependency files for load ordering
  widgets/
    box.wgt                  VBox/HBox/Frame containers
    button.wgt               push button
    ...                      (26 widget modules total)
    *.dep                    dependency files
  apps/
    progman/progman.app      Program Manager (desktop)
    notepad/notepad.app      text editor
    clock/clock.app          clock display
    dvxdemo/dvxdemo.app      widget showcase
    cpanel/cpanel.app        control panel
    imgview/imgview.app      image viewer
  config/
    dvx.ini                  system configuration
    themes/                  color theme files (.thm)
    wpaper/                  wallpaper images

Core Architecture (5 Layers)

1. dvxVideo -- VESA VBE init, LFB mapping, backbuffer, pixel format, color packing
2. dvxDraw -- Rectangle fills, bevels, text rendering, cursor/icon drawing
3. dvxComp -- Dirty rectangle tracking, merge, compositor, LFB flush
4. dvxWm -- Window stack, chrome, drag/resize, menus, scrollbars, hit testing
5. dvxApp -- Event loop, input polling, public API, color schemes, wallpaper

Widget System

Widgets are isolated DXE modules. Core knows nothing about individual widget types -- no compile-time enum, no union, no per-widget structs in dvxWidget.h.

• Dynamic type IDs: wgtRegisterClass() assigns IDs at load time
• *void data: Each widget allocates its own private data struct
• ABI-stable dispatch: WidgetClassT.handlers[] is an array of function pointers indexed by WGT_METHOD_* constants (0-20, room for 32). Core dispatches via w->wclass->handlers[WGT_METHOD_PAINT] etc., so adding new methods does not break existing widget DXE binaries
• Generic drag: WGT_METHOD_ON_DRAG_UPDATE and WGT_METHOD_ON_DRAG_END provide widget-level drag support without per-widget hacks in core
• Per-widget API registry: wgtRegisterApi("name", &api) replaces the monolithic API
• Per-widget headers: widgets/widgetButton.h etc. provide typed macros
• Shared helpers: texthelp.lib (text editing) and listhelp.lib (dropdown/list)
• All limits dynamic: widget child arrays, app slots, and desktop callbacks are stb_ds dynamic arrays with no fixed maximums

DXE Module System

All modules are DXE3 dynamic libraries loaded by dvx.exe at startup. The loader recursively scans libs/ for .lib files and widgets/ for .wgt files, reads .dep files for dependencies, and loads in topological order. Widget modules that export wgtRegister() have it called after loading.

Each .dep file lists base names of modules that must load first, one per line. Comments start with #.

App Types

Callback-only (hasMainLoop = false): appMain creates windows, registers callbacks, and returns. The app lives through event callbacks in the shell's main loop. No dedicated task or stack needed.

Main-loop (hasMainLoop = true): A cooperative task is created for the app. appMain runs its own loop calling tsYield() to share CPU. Used for apps that need continuous processing (clocks, terminal emulators, games).

Crash Recovery

The shell installs signal handlers for SIGSEGV, SIGFPE, and SIGILL before loading any apps, so even crashes during app initialization are caught. If an app crashes, the handler longjmps back to the shell's main loop, the crashed app is force-killed, and the shell continues running. Diagnostic information (registers, faulting EIP) is logged to dvx.log.

Bundled Applications

App	File	Type	Description
Program Manager	progman.app	Callback	App launcher grid, system info dialog
Notepad	notepad.app	Callback	Text editor with File/Edit menus, open/save, clipboard
Clock	clock.app	Main-loop	Digital clock display; multi-instance capable
DVX Demo	dvxdemo.app	Callback	Widget system showcase demonstrating 31 widget types
Control Panel	cpanel.app	Callback	Themes, wallpaper, video mode, mouse configuration
Image Viewer	imgview.app	Callback	Displays BMP, PNG, JPEG, GIF images with aspect-ratio zoom

Serial / Networking Stack

A layered encrypted serial communications stack for connecting DVX to remote systems (BBS, etc.) through 86Box's emulated UART:

Layer	Library	Description
rs232	librs232.a	ISR-driven UART driver, ring buffers, flow control
packet	libpacket.a	HDLC framing, CRC-16, Go-Back-N ARQ
security	libsecurity.a	1024-bit DH, XTEA-CTR cipher, DRBG RNG
seclink	libseclink.a	Channel multiplexing, per-packet encryption
proxy	secproxy	Linux bridge: 86Box serial <-> telnet BBS

Third-Party Dependencies

All third-party code is vendored as single-header libraries:

Library	Location	Purpose
stb_image.h	core/thirdparty/	Image loading (BMP, PNG, JPEG, GIF)
stb_image_write.h	core/thirdparty/	PNG export for screenshots
stb_ds.h	core/thirdparty/	Dynamic arrays and hash maps

stb_ds implementation is compiled into dvx.exe (the loader) with STBDS_REALLOC/STBDS_FREE overridden to use dvxRealloc/dvxFree, so all arrput/arrfree calls in DXE code are tracked per-app. The functions are exported via dlregsym to all DXE modules.

Target Hardware

• CPU: 486 baseline, Pentium-optimized paths where significant
• Video: VESA VBE 2.0+ with LFB (no bank switching)
• Platform: 86Box emulator (trusted reference), real DOS hardware
• Resolutions: 640x480, 800x600, 1024x768 at 8/15/16/32 bpp