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<!DOCTYPE html>
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<title>DVX Architecture Overview</title>
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<h3>Contents</h3>
<ul>
<li><a href="#arch.overview">System Overview</a></li>
<li><a href="#arch.layers">Five-Layer Architecture</a></li>
<li><a href="#arch.pipeline">Display Pipeline</a></li>
<li><a href="#arch.windows">Window System</a></li>
<li><a href="#arch.widgets">Widget System</a></li>
<li><a href="#arch.dxe">DXE Module System</a></li>
<li><a href="#arch.events">Event Model</a></li>
<li><a href="#arch.fonts">Font System</a></li>
<li><a href="#arch.colors">Color System</a></li>
<li><a href="#arch.platform">Platform Layer</a></li>
<li><a href="#arch.build">Build System</a></li>
</ul>
<h3>Index</h3>
<ul>
<li><a href="#arch.overview">DVX</a></li>
<li><a href="#arch.overview">Architecture</a></li>
<li><a href="#arch.overview">DJGPP</a></li>
<li><a href="#arch.overview">DPMI</a></li>
<li><a href="#arch.layers">Layers</a></li>
<li><a href="#arch.layers">dvxVideo</a></li>
<li><a href="#arch.layers">dvxDraw</a></li>
<li><a href="#arch.layers">dvxComp</a></li>
<li><a href="#arch.layers">dvxWm</a></li>
<li><a href="#arch.layers">dvxApp</a></li>
<li><a href="#arch.pipeline">Display Pipeline</a></li>
<li><a href="#arch.pipeline">Backbuffer</a></li>
<li><a href="#arch.pipeline">Linear Framebuffer</a></li>
<li><a href="#arch.pipeline">LFB</a></li>
<li><a href="#arch.pipeline">Dirty Rects</a></li>
<li><a href="#arch.pipeline">Double Buffer</a></li>
<li><a href="#arch.pipeline">Compositing</a></li>
<li><a href="#arch.pipeline">DisplayT</a></li>
<li><a href="#arch.pipeline">BlitOpsT</a></li>
<li><a href="#arch.pipeline">DirtyListT</a></li>
<li><a href="#arch.windows">Window</a></li>
<li><a href="#arch.windows">WindowT</a></li>
<li><a href="#arch.windows">Z-Order</a></li>
<li><a href="#arch.windows">Chrome</a></li>
<li><a href="#arch.windows">Hit Testing</a></li>
<li><a href="#arch.windows">Menu System</a></li>
<li><a href="#arch.windows">Minimized Windows</a></li>
<li><a href="#arch.windows">Window Stack</a></li>
<li><a href="#arch.windows">Menus</a></li>
<li><a href="#arch.windows">Submenus</a></li>
<li><a href="#arch.widgets">Widgets</a></li>
<li><a href="#arch.widgets">WidgetT</a></li>
<li><a href="#arch.widgets">WidgetClassT</a></li>
<li><a href="#arch.widgets">Layout Engine</a></li>
<li><a href="#arch.widgets">Widget API</a></li>
<li><a href="#arch.widgets">Layout</a></li>
<li><a href="#arch.widgets">Flexbox</a></li>
<li><a href="#arch.widgets">WgtIfaceT</a></li>
<li><a href="#arch.dxe">DXE</a></li>
<li><a href="#arch.dxe">DXE3</a></li>
<li><a href="#arch.dxe">Modules</a></li>
<li><a href="#arch.dxe">Dynamic Loading</a></li>
<li><a href="#arch.dxe">Boot Sequence</a></li>
<li><a href="#arch.dxe">Crash Recovery</a></li>
<li><a href="#arch.dxe">Memory Tracking</a></li>
<li><a href="#arch.events">Events</a></li>
<li><a href="#arch.events">Input</a></li>
<li><a href="#arch.events">Mouse</a></li>
<li><a href="#arch.events">Keyboard</a></li>
<li><a href="#arch.events">Polling</a></li>
<li><a href="#arch.events">Cooperative</a></li>
<li><a href="#arch.events">Event Dispatch</a></li>
<li><a href="#arch.events">Accelerator Tables</a></li>
<li><a href="#arch.events">Cursor</a></li>
<li><a href="#arch.events">Double-Click</a></li>
<li><a href="#arch.fonts">Fonts</a></li>
<li><a href="#arch.fonts">Bitmap Font</a></li>
<li><a href="#arch.fonts">BitmapFontT</a></li>
<li><a href="#arch.fonts">Text Rendering</a></li>
<li><a href="#arch.fonts">CP437</a></li>
<li><a href="#arch.colors">Colors</a></li>
<li><a href="#arch.colors">Pixel Format</a></li>
<li><a href="#arch.colors">PixelFormatT</a></li>
<li><a href="#arch.colors">ColorSchemeT</a></li>
<li><a href="#arch.colors">Theming</a></li>
<li><a href="#arch.colors">Bevel</a></li>
<li><a href="#arch.platform">Platform Layer</a></li>
<li><a href="#arch.platform">dvxPlatform</a></li>
<li><a href="#arch.platform">VESA</a></li>
<li><a href="#arch.platform">VBE</a></li>
<li><a href="#arch.platform">INT 33h</a></li>
<li><a href="#arch.platform">INT 16h</a></li>
<li><a href="#arch.platform">Assembly</a></li>
<li><a href="#arch.platform">rep stosl</a></li>
<li><a href="#arch.platform">rep movsd</a></li>
<li><a href="#arch.build">Build</a></li>
<li><a href="#arch.build">Makefile</a></li>
<li><a href="#arch.build">Cross-Compilation</a></li>
<li><a href="#arch.build">dxe3gen</a></li>
<li><a href="#arch.build">mkcd.sh</a></li>
<li><a href="#arch.build">ISO</a></li>
</ul>
</nav>
<main>
<div class="topic" id="arch.overview">
<h1>DVX Architecture Overview</h1>
<h2>DVX Architecture Overview</h2>
<p>DOS Visual eXecutive -- A Windowing GUI for DJGPP/DPMI</p>
<p>DVX (DOS Visual eXecutive) is a complete windowing GUI compositor targeting
DJGPP/DPMI on DOS. It provides overlapping windows with Motif-style chrome,
a retained-mode widget toolkit, cooperative multitasking of DXE-loaded
applications, and a dirty-rectangle compositor optimized for 486/Pentium
hardware.</p>
<h3>Key Design Constraints</h3>
<ul>
<li>VESA VBE 2.0+ LFB only -- no bank switching. If the hardware cannot
provide a linear framebuffer, initialization fails.</li>
<li>486 baseline -- all hot paths are written to be fast on a 486, with
Pentium-specific paths where the gain is significant.</li>
<li>Single-tasking cooperative model -- applications yield the CPU via
tsYield(); there is no preemptive scheduler.</li>
<li>86Box is the trusted reference platform for testing. DOSBox-X is not used;
any bugs observed are treated as DVX bugs.</li>
</ul>
<p>No external font or cursor files -- all bitmaps are compiled in as static
const data.</p>
<p>The runtime environment consists of a bootstrap loader (dvx.exe) that loads
core DXE libraries, widget plugins, and the shell, which in turn loads and
manages DXE application modules.</p>
<h3>Contents</h3>
<ul>
<li>.link arch.overview System Overview</li>
<li>.link arch.layers Five-Layer Architecture</li>
<li>.link arch.pipeline Display Pipeline</li>
<li>.link arch.windows Window System</li>
<li>.link arch.widgets Widget System</li>
<li>.link arch.dxe DXE Module System</li>
<li>.link arch.events Event Model</li>
<li>.link arch.fonts Font System</li>
<li>.link arch.colors Color System</li>
<li>.link arch.platform Platform Layer</li>
</ul>
<p>.link arch.build Build System</p>
</div>
<div class="topic" id="arch.layers">
<h1>Five-Layer Architecture</h1>
<h2>Five-Layer Architecture</h2>
<p>DVX is organized into five layers, each implemented as a single .h/.c pair.
Every header includes dvxTypes.h (the shared type definitions) to avoid
circular dependencies. The layers are strictly stacked: each layer depends
only on the layers below it.</p>
<pre><code> Applications (DXE .app modules)
==================================================
| |
| +------------------------------------------+ |
| | Layer 5: dvxApp (Application API) | | dvxApp.h / dvxApp.c
| | Event loop, window creation, public API | |
| +------------------------------------------+ |
| | Layer 4: dvxWm (Window Manager) | | dvxWm.h / dvxWm.c
| | Window stack, chrome, drag, resize | |
| +------------------------------------------+ |
| | Layer 3: dvxComp (Compositor) | | dvxComp.h / dvxComp.c
| | Dirty rect tracking, merge, LFB flush | |
| +------------------------------------------+ |
| | Layer 2: dvxDraw (Drawing Primitives) | | dvxDraw.h / dvxDraw.c
| | Rects, bevels, text, blits, cursors | |
| +------------------------------------------+ |
| | Layer 1: dvxVideo (Video Backend) | | dvxVideo.h / dvxVideo.c
| | VESA VBE, LFB mapping, pixel format | |
| +------------------------------------------+ |
| |
| +------------------------------------------+ |
| | Platform Layer (dvxPlatform.h) | | dvxPlatformDos.c
| | OS-specific: video, input, asm spans | |
| +------------------------------------------+ |
| |
| +------------------------------------------+ |
| | Shared Types (dvxTypes.h) | |
| | DisplayT, WindowT, RectT, ColorSchemeT | |
| +------------------------------------------+ |
==================================================</code></pre>
<h3>Layer Summary</h3>
<pre> Layer Header Responsibility
----- ------ --------------
1 - Video dvxVideo.h VESA VBE mode negotiation, LFB mapping via DPMI, backbuffer allocation, packColor() (RGB to native pixel format), display-wide clip rectangle.
2 - Draw dvxDraw.h All 2D drawing: rectFill, rectCopy, drawBevel, drawText/drawTextN, drawMaskedBitmap (cursor), drawTermRow (batch terminal row). Stateless beyond clip rect. Dispatches hot inner loops through BlitOpsT function pointers.
3 - Compositor dvxComp.h Dirty rectangle tracking (dirtyListAdd), pairwise merge of overlapping rects (dirtyListMerge), and flushRect to copy dirty regions from backBuf to LFB.
4 - Window Manager dvxWm.h Window lifecycle, Z-order stack, chrome drawing (title bars, bevels, close/minimize/maximize gadgets), hit testing, drag/resize, menu bars, scrollbars, system menu, keyboard move/resize, minimized icon bar.
5 - Application dvxApp.h Public API aggregating all layers into AppContextT. Provides dvxInit/dvxShutdown, dvxRun/dvxUpdate, window creation helpers, image loading, clipboard, accelerator tables, theme management, wallpaper, video mode switching, screenshot capture.</pre>
</div>
<div class="topic" id="arch.pipeline">
<h1>Display Pipeline</h1>
<h2>Display Pipeline</h2>
<p>The double-buffer strategy is the single most important performance decision
in DVX. All drawing goes to a system RAM backbuffer (DisplayT.backBuf); only
dirty rectangles are flushed to the linear framebuffer (DisplayT.lfb) in
video memory.</p>
<p>This matters because writes to video memory over the PCI bus are 10-50x
slower than writes to main RAM on 486/Pentium hardware for random-access
patterns.</p>
<h3>Per-Frame Compositing Pipeline</h3>
<pre><code> 1. Input poll (mouse, keyboard)
|
2. Event dispatch (focus window callbacks)
|
3. Layers call dirtyListAdd() for changed regions
|
4. dirtyListMerge() consolidates overlapping rects
|
5. For each merged dirty rect:
a. Clip and redraw desktop background (or wallpaper)
b. For each window (back-to-front, painter's algorithm):
- wmDrawChrome() -- frame, title bar, gadgets, menu bar
- wmDrawContent() -- blit per-window content buffer
- wmDrawScrollbars()
c. Draw minimized window icons
d. Draw popup menus / tooltips (overlay pass)
e. Draw software mouse cursor
|
6. flushRect() -- copy each dirty rect from backBuf to LFB
|
7. Yield (platformYield)</code></pre>
<h3>Key Data Structures</h3>
<p>DisplayT -- Central display context: width, height, pitch, pixel format, LFB
pointer, backbuffer pointer, palette, clip rectangle. Passed by pointer
through every layer -- no globals.</p>
<p>BlitOpsT -- Vtable of span fill/copy function pointers resolved at init time
for the active pixel depth. On DOS these dispatch to hand-written rep stosl
/ rep movsd asm inner loops.</p>
<p>DirtyListT -- Fixed-capacity dynamic array of RectT. Linear scanning for
merge candidates is cache-friendly at typical sizes (under 128 rects). If
the list fills up, the compositor merges aggressively or falls back to
full-screen repaint.</p>
<h3>Why This Works on a 486</h3>
<ul>
<li>A full 640x480x32bpp frame is 1.2 MB -- far too much to flush every frame
over a slow PCI bus.</li>
<li>A typical dirty region during normal interaction (typing, menu open) is a
few KB.</li>
<li>Merging overlapping dirty rects into larger rects reduces per-rect
overhead and improves bus utilization.</li>
</ul>
<p>Per-window content buffers persist across frames, so windows don't repaint
on expose -- only when their own content changes.</p>
</div>
<div class="topic" id="arch.windows">
<h1>Window System</h1>
<h2>Window System</h2>
<h3>WindowT Structure</h3>
<p>Each WindowT is the central object of the window manager. Key fields:</p>
<pre> Field Group Purpose
----------- -------
Geometry (x, y, w, h) Outer frame rectangle (including chrome).
Content area (contentX/Y/W/H) Computed from frame minus chrome. Where application content lives.
Content buffer (contentBuf, contentPitch) Per-window backbuffer in native pixel format. Persists across frames.
Chrome state (menuBar, vScroll, hScroll) Optional menu bar and scrollbars. Affect content area computation.
Widget tree (widgetRoot) Root of the retained-mode widget tree (NULL if using raw callbacks).
Callbacks onPaint, onKey, onKeyUp, onMouse, onResize, onClose, onMenu, onScroll, onFocus, onBlur, onCursorQuery.</pre>
<h3>Window Stack (Z-Order)</h3>
<p>WindowStackT is an array of WindowT* ordered front-to-back: index count-1 is
the topmost window. This allows:</p>
<ul>
<li>Back-to-front iteration for painting (painter's algorithm).</li>
<li>Front-to-back iteration for hit testing (first hit wins).</li>
</ul>
<p>Reordering by pointer swap (no copying of large WindowT structs).</p>
<p>Only one drag/resize/scroll operation can be active system-wide at a time
(single mouse), so that state lives on the stack, not on individual windows.</p>
<h3>Chrome Layout</h3>
<pre><code> +-------------------------------------------+
| 4px outer border (raised bevel) |
| +-------------------------------------+ |
| | [X] Title Bar Text [_] [^] [X] | | 20px title height
| +-------------------------------------+ |
| | 2px inner border | |
| +-------------------------------------+ |
| | Menu Bar (optional, 20px) | |
| +-------------------------------------+ |
| | | |
| | Content Area | |
| | | |
| | | S | | S = vertical scrollbar
| | | B | | (16px wide)
| +-------------------------------------+ |
| | Horizontal Scrollbar (optional) | | 16px tall
| +-------------------------------------+ |
| 4px outer border |
+-------------------------------------------+</code></pre>
<p>Chrome constants are compile-time defines:</p>
<pre><code> CHROME_BORDER_WIDTH = 4px
CHROME_TITLE_HEIGHT = 20px
CHROME_INNER_BORDER = 2px
CHROME_MENU_HEIGHT = 20px
SCROLLBAR_WIDTH = 16px
CHROME_CLOSE_BTN_SIZE = 16px</code></pre>
<h3>Hit Test Regions</h3>
<p>wmHitTest() iterates the stack front-to-back and returns a hit-part
identifier: HIT_CONTENT, HIT_TITLE, HIT_CLOSE, HIT_RESIZE, HIT_MENU,
HIT_VSCROLL, HIT_HSCROLL, HIT_MINIMIZE, HIT_MAXIMIZE. Resize edge detection
returns a bitmask of RESIZE_LEFT, RESIZE_RIGHT, RESIZE_TOP, RESIZE_BOTTOM
(corners combine two edges).</p>
<h3>Menu System</h3>
<p>Menus use fixed-size arrays with inline char buffers (no heap strings). Up
to 8 menus per bar, items dynamically allocated. Supports cascading submenus
via MenuItemT.subMenu pointer. Item types: normal, checkbox, radio.
Separators are non-interactive items. The popup state (PopupStateT) tracks a
stack of parent frames for cascading submenu nesting.</p>
<h3>Minimized Windows</h3>
<p>Minimized windows display as 64x64 icons at the bottom of the screen with
beveled borders, similar to a classic desktop icon bar. Icons show a
scaled-down preview of the window's content buffer, refreshed one per frame
in a round-robin fashion to amortize the scaling cost.</p>
</div>
<div class="topic" id="arch.widgets">
<h1>Widget System</h1>
<h2>Widget System</h2>
<p>The widget system (dvxWidget.h) is a retained-mode toolkit layered on top of
the window manager. Widgets form a tree rooted at a per-window VBox
container.</p>
<h3>WidgetT Base Structure</h3>
<p>Every widget shares the same WidgetT struct. The type field is a
runtime-assigned integer ID. The wclass pointer references the widget's
WidgetClassT vtable. Widget-specific private data is stored in w-&gt;data
(opaque void*).</p>
<p>Tree linkage: parent, firstChild, lastChild, nextSibling. No prevSibling --
this halves pointer overhead and removal is still O(n) for typical tree
depths of 5-10.</p>
<h3>Layout Engine</h3>
<p>Two-pass flexbox-like algorithm:</p>
<ul>
<li>Bottom-up (calcMinSize) -- compute minimum sizes for every widget,
starting from leaves.</li>
</ul>
<p>Top-down (layout) -- allocate space within available bounds, distributing
extra space according to weight values (0 = fixed, 100 = normal stretch).</p>
<p>Size hints use a tagged encoding: the top 2 bits of an int32_t select the
unit (pixels, character widths, or percentage of parent), the low 30 bits
hold the value. Macros: wgtPixels(v), wgtChars(v), wgtPercent(v).</p>
<h3>Widget Class Dispatch (WidgetClassT)</h3>
<p>Each widget type provides a WidgetClassT with a handlers[] array indexed by
stable method IDs. Method IDs are never reordered or reused -- new methods
append at the end. This provides ABI-stable dispatch so that widget DXEs
compiled against an older DVX version continue to work.</p>
<p>Methods include: PAINT, PAINT_OVERLAY, CALC_MIN_SIZE, LAYOUT, ON_MOUSE,
ON_KEY, ON_ACCEL_ACTIVATE, DESTROY, GET_TEXT, SET_TEXT, POLL, and more (21
defined, room for 32).</p>
<h4>Class Flags</h4>
<pre> Flag Meaning
---- -------
WCLASS_FOCUSABLE Can receive keyboard focus (Tab navigation)
WCLASS_HORIZ_CONTAINER Lays out children horizontally (HBox)
WCLASS_PAINTS_CHILDREN Widget handles child rendering itself
WCLASS_SCROLLABLE Accepts mouse wheel events
WCLASS_SCROLL_CONTAINER ScrollPane -- scrolling viewport
WCLASS_NEEDS_POLL Needs periodic polling (e.g. AnsiTerm comms)
WCLASS_SWALLOWS_TAB Tab key goes to widget, not focus navigation
WCLASS_PRESS_RELEASE Click = press + release (buttons)</pre>
<h3>Available Widget Types</h3>
<p>Each widget is a separate .wgt DXE module. 29 widget types are included:</p>
<pre> Widget Description
------ -----------
Box (VBox/HBox) Vertical and horizontal layout containers
Button Clickable push button with label
Canvas Raw drawing surface for custom painting
Checkbox Boolean toggle with checkmark
ComboBox Text input with dropdown list
DataCtrl Data-bound control for database operations
DbGrid Database grid (tabular data display)
Dropdown Dropdown selection list
Image Static image display
ImageButton Button with bitmap icon
Label Static text label
ListBox Scrollable selection list
ListView Multi-column list with headers and sorting
ProgressBar Determinate progress indicator
Radio Radio button (mutual exclusion group)
ScrollPane Scrollable viewport container
Separator Visual divider line
Slider Value selection via draggable thumb
Spacer Empty space for layout
Spinner Numeric input with up/down arrows
Splitter Resizable split pane
StatusBar Window status bar with sections
TabControl Tabbed page container
Terminal (AnsiTerm) ANSI terminal emulator widget
TextInput Single-line text entry field
Timer Periodic timer events
Toolbar Toolbar with icon buttons
TreeView Hierarchical tree display
WrapBox Flow layout (wrapping horizontal container)</pre>
<h3>Widget API Registry</h3>
<p>Each widget DXE registers a small API struct under a name during
wgtRegister(). Callers retrieve it via wgtGetApi(&quot;button&quot;) and cast to the
widget-specific API type. Per-widget headers provide typed accessors so
callers avoid manual casts. Adding a new widget requires zero changes to the
core.</p>
<h3>Widget Interface Descriptors (WgtIfaceT)</h3>
<p>Each widget can register an interface descriptor that describes its
BASIC-facing properties, methods, and events. These descriptors are used by
the form runtime and IDE for generic dispatch and property panel
enumeration. Properties have typed getters/setters (WGT_IFACE_STRING,
WGT_IFACE_INT, WGT_IFACE_BOOL, WGT_IFACE_ENUM).</p>
</div>
<div class="topic" id="arch.dxe">
<h1>DXE Module System</h1>
<h2>DXE Module System</h2>
<p>DVX uses DJGPP's DXE3 (Dynamic eXtension) format for all loadable modules.
DXE3 supports RTLD_GLOBAL symbol sharing -- symbols exported by one module
are visible to all subsequently loaded modules. This is critical: widget
DXEs call core API functions (e.g. rectFill, wgtInvalidate) that are
exported by the core library DXE.</p>
<h3>Module Types</h3>
<pre> Extension Directory Purpose Examples
--------- --------- ------- --------
.lib LIBS/ Core libraries loaded first. Provide infrastructure APIs. libtasks.lib, libdvx.lib, dvxshell.lib
.wgt WIDGETS/ Widget type plugins. Each exports wgtRegister(). button.wgt, listview.wgt, terminal.wgt
.app APPS/*/ Application modules. Each exports appDescriptor and appMain(). Loaded on demand by the shell. progman.app, notepad.app, cpanel.app</pre>
<h3>Boot Sequence</h3>
<pre><code> dvx.exe (loader)
|
+-- Enter VGA mode 13h, display splash screen with progress bar
|
+-- Scan LIBS/ for *.lib, WIDGETS/ for *.wgt
|
+-- Read .dep files for each module (dependency base names)
|
+-- Topological sort: load modules in dependency order
| - dlopen() with RTLD_GLOBAL
| - Each .wgt that exports wgtRegister() has it called
|
+-- Find and call shellMain() (exported by dvxshell.lib)
|
+-- dvxInit() -- video mode, input, font, colors, cursors
|
+-- Load desktop app (progman.app)
|
+-- Main loop:
dvxUpdate() -&gt; tsYield() -&gt; shellReapApps()</code></pre>
<h3>Application Lifecycle</h3>
<p>Two kinds of DXE apps:</p>
<h4>Callback-only (hasMainLoop = false)</h4>
<p>appMain() creates windows, registers callbacks, and returns. The app lives
through GUI callbacks driven by the shell's main loop. Lifecycle ends when
the last window is closed. No extra task stack needed -- simpler and
cheaper.</p>
<h4>Main-loop (hasMainLoop = true)</h4>
<p>A dedicated cooperative task is created. appMain() runs in that task with
its own loop, calling tsYield() to share CPU. Needed for apps with
continuous work (terminal emulators, games). Lifecycle ends when appMain()
returns.</p>
<h3>Crash Recovery</h3>
<p>The platform layer installs signal handlers for SIGSEGV, SIGFPE, SIGILL. On
crash, the handler logs platform-specific diagnostics (register dump on
DJGPP), then longjmps back to the shell's main loop. The crashed app is
killed; other apps and the shell survive. This provides Windows 3.1-style
fault tolerance.</p>
<h3>Per-App Memory Tracking</h3>
<p>All allocations route through dvxMalloc/dvxFree wrappers that prepend a
16-byte header recording the owning app ID and allocation size. The Task
Manager displays per-app memory usage, and leaks are detected at app
termination.</p>
</div>
<div class="topic" id="arch.events">
<h1>Event Model</h1>
<h2>Event Model</h2>
<p>DVX uses a cooperative polling model. The main loop (dvxRun / dvxUpdate)
runs this cycle each frame:</p>
<ul>
<li>Poll mouse -- platformMousePoll() returns position and button bitmask.
Compare with previous frame for press/release edge detection.</li>
<li>Poll keyboard -- platformKeyboardRead() returns ASCII + scancode.
Non-blocking; returns false if buffer is empty.</li>
<li>Dispatch to focused window -- the event loop fires window callbacks
(onKey, onMouse, etc.) on the focused window. If the window has a widget
tree, the widget system's installed handlers dispatch to individual
widgets.</li>
<li>Compositor pass -- merge dirty rects, composite, flush to LFB.</li>
</ul>
<p>Yield -- platformYield() or idle callback.</p>
<h3>Event Dispatch Chain</h3>
<pre><code> Mouse/Keyboard Input
|
Global handlers (Ctrl+Esc, modal filter)
|
Accelerator table check (focused window)
|
Window callback (onMouse / onKey)
|
[If widget tree installed:]
|
widgetOnMouse / widgetOnKey
|
Widget hit test (widgetHitTest)
|
wclsOnMouse / wclsOnKey (vtable dispatch)
|
Universal callbacks (onClick, onChange, etc.)</code></pre>
<h3>Accelerator Tables</h3>
<p>Per-window accelerator tables map key + modifier combinations to command
IDs. The runtime normalizes key/modifier at registration time (uppercase
key, strip shift from modifiers) so matching at dispatch time is two integer
comparisons per entry. Matched accelerators fire the window's onMenu
callback with the command ID, unifying the menu and hotkey code paths.</p>
<h3>Mouse Cursor</h3>
<p>Software-rendered cursor using the classic AND/XOR mask approach. Seven
cursor shapes are compiled in: arrow, horizontal resize, vertical resize,
NW-SE diagonal resize, NE-SW diagonal resize, busy (hourglass), and
crosshair. The cursor is painted into the backbuffer on top of the
composited frame and the affected region is flushed to the LFB each frame.</p>
<h3>Double-Click Detection</h3>
<p>Timestamp-based: two clicks on the same target (title bar, minimized icon,
close gadget) within the configurable double-click interval trigger the
double-click action. Separate tracking for each target type.</p>
</div>
<div class="topic" id="arch.fonts">
<h1>Font System</h1>
<h2>Font System</h2>
<p>DVX uses fixed-width 8-pixel-wide bitmap fonts only. One size is provided:
8x16, matching the standard VGA ROM font and CP437 encoding (256 glyphs).</p>
<h3>BitmapFontT</h3>
<pre><code> typedef struct {
int32_t charWidth; // fixed width per glyph (always 8)
int32_t charHeight; // 16
int32_t firstChar; // typically 0
int32_t numChars; // typically 256
const uint8_t *glyphData; // packed 1bpp, charHeight bytes per glyph
} BitmapFontT;</code></pre>
<p>Design rationale:</p>
<ul>
<li>Character positions are pure multiplication (x = col * 8).</li>
<li>Glyph lookup is a single array index.</li>
<li>Each scanline of a glyph is exactly one byte (1bpp at 8 pixels wide).</li>
<li>No glyph-width tables, kerning, or per-character positioning needed.</li>
</ul>
<p>8-pixel width aligns with byte boundaries -- no bit shifting in per-scanline
rendering.</p>
<h3>Text Rendering Functions</h3>
<p>drawChar() -- Renders a single character. Supports opaque (background fill)
and transparent modes.</p>
<p>drawTextN() -- Optimized batch rendering for a known character count. Clips
once for the entire run, fills background in a single rectFill, then
overlays glyph foreground pixels. Significantly faster than per-character
rendering for long runs.</p>
<p>drawTermRow() -- Renders an 80-column terminal row in a single pass, with
per-cell foreground/background from a 16-color palette, blink attribute
support, and cursor rendering. Exists because per-character terminal
rendering is unacceptably slow on target hardware.</p>
<p>drawTextAccel() -- Renders text with &amp; accelerator markers. The character
after &amp; is underlined to indicate the keyboard shortcut.</p>
<h3>Performance Optimization</h3>
<p>AppContextT stores a fixed-point 16.16 reciprocal of font.charHeight
(charHeightRecip) so that dividing by charHeight (for pixel-to-row
conversion in terminal/text widgets) becomes a multiply+shift instead of an
integer divide, which costs 40+ cycles on a 486.</p>
</div>
<div class="topic" id="arch.colors">
<h1>Color System</h1>
<h2>Color System</h2>
<h3>Pixel Format</h3>
<p>PixelFormatT describes the active VESA mode's pixel encoding. Populated once
from the VBE mode info block. Stores shift, mask, and bit count for each
channel so packColor() can convert RGB to native format with shift-and-mask
arithmetic -- no per-pixel computation.</p>
<p>Supported depths:</p>
<pre> Depth Bytes/Pixel Notes
----- ----------- -----
8 bpp 1 Palette mode. Nearest-index via 6x6x6 color cube + grey ramp.
15 bpp 2 5-5-5 RGB (1 bit unused).
16 bpp 2 5-6-5 RGB.
32 bpp 4 8-8-8 RGB (8 bits unused).</pre>
<h3>ColorSchemeT -- Theming</h3>
<p>All 20 UI colors are pre-packed into display pixel format at init time.
Every color is a uint32_t that can be written directly to the framebuffer
with zero per-pixel conversion. The scheme must be regenerated on video mode
change, but mode changes require re-init anyway.</p>
<p>Color roles mirror classic Motif/Windows 3.x conventions:</p>
<ul>
<li>desktop -- desktop background</li>
<li>windowFace, windowHighlight, windowShadow -- window chrome bevel triplet</li>
<li>activeTitleBg/Fg, inactiveTitleBg/Fg -- focused vs. unfocused title bar</li>
<li>contentBg/Fg -- window content area</li>
<li>menuBg/Fg, menuHighlightBg/Fg -- menus</li>
<li>buttonFace -- button background</li>
<li>scrollbarBg/Fg/Trough -- scrollbar components</li>
</ul>
<p>cursorFg/Bg -- mouse cursor colors</p>
<p>Source RGB values are kept in AppContextT.colorRgb[] for theme save/load.
Themes are stored as INI files with a [colors] section. The API provides
dvxLoadTheme(), dvxSaveTheme(), dvxSetColor(), and dvxResetColorScheme().</p>
<h3>Bevel Styles</h3>
<p>Bevels are the defining visual element of the Motif aesthetic. Convenience
macros create bevel style descriptors by swapping highlight and shadow
colors:</p>
<pre><code> BEVEL_RAISED(colorScheme, borderWidth) -- raised 3D look
BEVEL_SUNKEN(colorScheme, face, borderWidth) -- sunken/inset look
BEVEL_TROUGH(colorScheme) -- 1px scrollbar trough
BEVEL_SB_BUTTON(colorScheme) -- scrollbar button</code></pre>
</div>
<div class="topic" id="arch.platform">
<h1>Platform Layer</h1>
<h2>Platform Layer</h2>
<p>All OS-specific and CPU-specific code is isolated behind dvxPlatform.h. To
port DVX, implement a new dvxPlatformXxx.c against this header.</p>
<h3>Implementations</h3>
<pre> File Target Details
---- ------ -------
dvxPlatformDos.c DJGPP/DPMI Real VESA VBE, INT 33h mouse, INT 16h keyboard, rep movsd/rep stosl asm spans, DPMI physical memory mapping for LFB, INT 9 hook for key-up, CuteMouse Wheel API.</pre>
<h3>Abstraction Areas</h3>
<h4>Video</h4>
<p>platformVideoInit() -- mode probe and framebuffer setup.
platformVideoShutdown() -- restore previous mode. platformVideoEnumModes()
-- enumerate available modes.</p>
<h4>Framebuffer Flush</h4>
<p>platformFlushRect() -- copy dirty rect from backBuf to LFB. On DOS, each
scanline uses rep movsd for near-optimal aligned 32-bit writes over the PCI
bus.</p>
<h4>Optimized Memory Spans</h4>
<p>Six functions: platformSpanFill8/16/32() and platformSpanCopy8/16/32().
Called once per scanline of every rectangle fill, blit, and text draw. On
DOS these use inline assembly for critical inner loops.</p>
<h4>Mouse Input</h4>
<p>Polling model. platformMousePoll() returns position and button bitmask.
Wheel support via CuteMouse API.</p>
<h4>Keyboard Input</h4>
<p>platformKeyboardRead() -- non-blocking key read. platformKeyUpRead() -- key
release detection (requires INT 9 hook on DOS). platformAltScanToChar() --
scancode-to-ASCII lookup for Alt+key combinations.</p>
<h4>Crash Recovery</h4>
<p>platformInstallCrashHandler() -- signal handlers + longjmp for fault
tolerance.</p>
<h4>DXE Support</h4>
<p>platformRegisterDxeExports() -- register C runtime and platform symbols for
DXE resolution. platformRegisterSymOverrides() -- register function pointer
overrides for module loader.</p>
</div>
<div class="topic" id="arch.build">
<h1>Build System</h1>
<h2>Build System</h2>
<h3>Cross-Compilation</h3>
<p>DVX is cross-compiled from Linux using a DJGPP cross-compiler
(i586-pc-msdosdjgpp-gcc). The top-level Makefile orchestrates building all
subsystems in dependency order.</p>
<pre><code> make -- build everything
./mkcd.sh -- build + create ISO for 86Box</code></pre>
<h3>Build Targets</h3>
<pre><code> all: core tasks loader texthelp listhelp tools widgets shell taskmgr serial sql apps</code></pre>
<pre> Target Output Description
------ ------ -----------
core bin/libs/libdvx.lib GUI core library (draw, comp, wm, app, widget infrastructure)
tasks bin/libs/libtasks.lib Cooperative task switcher
loader bin/dvx.exe Bootstrap loader (the DOS executable)
widgets bin/widgets/*.wgt 29 widget type plugins
shell bin/libs/dvxshell.lib DVX Shell (app management, desktop)
taskmgr bin/libs/taskmgr.lib Task Manager (loaded as a separate DXE)
texthelp shared library Shared text editing helpers (clipboard, word boundaries)
listhelp shared library Shared dropdown/list helpers
apps bin/apps/*/*.app Application modules (progman, notepad, clock, etc.)
tools bin/dvxres Resource compiler (runs on Linux, builds resource sections into DXEs)
serial serial DXE libs UART driver, HDLC packets, security, seclink
sql SQL DXE lib SQLite integration</pre>
<h3>DXE3 Build Process</h3>
<p>Each DXE module is compiled to an object file with GCC, then linked with
dxe3gen:</p>
<pre><code> # Compile
i586-pc-msdosdjgpp-gcc -O2 -march=i486 -mtune=i586 -c -o widget.o widget.c
# Link as DXE with exported symbols
dxe3gen -o widget.wgt -E _wgtRegister -U widget.o
# Optionally append resources
dvxres build widget.wgt widget.res</code></pre>
<p>The -E flag specifies exported symbols (prefixed with underscore per DJGPP
convention). -U marks unresolved symbols as OK (they'll be resolved at load
time from previously loaded DXEs).</p>
<h3>Deployment (mkcd.sh)</h3>
<ul>
<li>Runs make all.</li>
<li>Verifies critical outputs exist (dvx.exe, libtasks.lib, libdvx.lib,
dvxshell.lib).</li>
<li>Counts widget modules.</li>
<li>Creates an ISO 9660 image from bin/ using mkisofs: -iso-level 1 (strict
8.3 filenames for DOS), -J (Joliet extensions for long names), -V DVX
(volume label).</li>
</ul>
<p>Places the ISO at ~/.var/app/net._86box._86Box/data/86Box/dvx.iso for 86Box
to mount as CD-ROM.</p>
<h3>Compiler Flags</h3>
<pre><code> -O2 Optimization level 2
-march=i486 486 instruction set baseline
-mtune=i586 Optimize scheduling for Pentium
-Wall -Wextra Full warnings</code></pre>
<h3>Directory Layout</h3>
<pre><code> dvxgui/
+-- core/ Core library sources (dvxVideo, dvxDraw, dvxComp, dvxWm, dvxApp, widget infra)
| +-- platform/ Platform abstraction (dvxPlatform.h, dvxPlatformDos.c)
| +-- thirdparty/ stb_image, stb_ds, stb_image_write
+-- loader/ Bootstrap loader (dvx.exe)
+-- tasks/ Cooperative task switcher (libtasks.lib)
+-- shell/ DVX Shell (dvxshell.lib)
+-- widgets/ Widget DXE modules (*.wgt), each in its own subdirectory
| +-- box/ VBox/HBox layout containers
| +-- button/ Push button
| +-- textInput/ Text entry field
| +-- listView/ Multi-column list
| +-- ... (29 widget types total)
+-- texthelp/ Shared text editing helpers
+-- listhelp/ Shared dropdown/list helpers
+-- apps/ Application DXE modules (*.app)
| +-- progman/ Program Manager (desktop)
| +-- notepad/ Text editor
| +-- cpanel/ Control Panel
| +-- imgview/ Image viewer
| +-- clock/ Clock
| +-- dvxdemo/ Demo / showcase app
| +-- dvxbasic/ DVX BASIC compiler and VM
+-- tools/ Build tools (dvxres resource compiler)
+-- rs232/ ISR-driven UART driver
+-- packet/ HDLC framing, CRC-16, sliding window
+-- security/ DH key exchange, XTEA cipher, DRBG RNG
+-- seclink/ Encrypted channel wrapper
+-- serial/ Combined serial stack DXE
+-- proxy/ Linux proxy (86Box &lt;-&gt; secLink &lt;-&gt; telnet)
+-- sql/ SQLite integration
+-- bin/ Build output (dvx.exe, libs/, widgets/, apps/, config/)
+-- obj/ Intermediate object files
+-- docs/ Documentation</code></pre>
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