SWOTL Enhanced

SWOTL Enhanced

Version 0.1.14

Run Secret Weapons of the Luftwaffe (Lucasfilm Games, 1991) on modern Windows without installing DOSBox. You need your own copy of the original game files. Tested with the original 1991 release and with the later 1994 release included in Lucasarts Air Combat Classics that included the P-38, P-80, He 162 and Do 335.

The original SWOTL.EXE and its overlay files run inside a small PC emulation layer made for this one game. The layer covers the x86 CPU, DOS, BIOS, VGA, AdLib, joystick and mouse. SDL3 handles the window, scaling, sound and gamepads.

What works

• Intro, menus, campaign map, briefing and flight. The game was tested up to the 3D flight with cockpit and controls.

• Display. Window or full screen, with the original 4:3 shape. Three scaling styles: sharp (crisp pixels with smooth edges), nearest and linear.

• CRT shader. By default the picture looks like a 1990s VGA monitor, with the CRT shaders and colour emulation of DOSBox Staging 0.83 (shader = crt-auto). See CRT shader below.

• Gamepad as joystick. The game's start-up joystick calibration is answered automatically.

• AdLib music and sound effects. Emulated with Nuked-OPL3.

• Mouse. The mouse is captured when you click in the window.

• Speed. The title bar shows the game's speed (speed): emulated time against real time. At 100% the game runs exactly as fast as on a real PC. If your PC cannot keep up, it drops below 100% and everything gets slower, the flying too.

• Frame rate. The emulated CPU speed adapts to your PC. The title bar shows the real 3D frame rate (fps; a dash outside the 3D view). It counts the game's own frame-present calls in the VGA driver. At 10 MIPS it is about 16 fps, at 20 MIPS about 34 fps and at 40 MIPS about 63 fps. The flight model runs on the game's 237 Hz timer, so the frame rate does not change how the aircraft handle.

• Keyboard flying. By default the arrow keys drive a smooth virtual joystick while you fly. Held down, the stick reaches full deflection in 0.25 s; released, it springs back to the centre in 0.12 s. Hold an arrow and the aircraft keeps rolling, as in the original. With keyboard_flight=classic the arrows go to the game as key presses, and every key repeat is one control step. Held keys repeat 30 times per second after 250 ms. That is the fast typematic setting of most 386/486 BIOSes and what DOSBox gives on Windows. With the slow power-on default of the keyboard (10.9 per second after 500 ms), the aircraft rolls about three times more slowly.

• Modified game copies. Some copies of SWOTL have a modified NOTCAMP.OVL that only works when the program is loaded at certain memory addresses. SWOTL Enhanced loads the game at an address where it works, so you get the Choose a side screen and clean menu text, just as in DOSBox. Unmodified copies are not affected.

The version number is shown in the title bar, at the top of swotl-enhanced.ini and in the file properties of the exe (right-click > Properties > Details).

Installation

1. Copy SWOTL-Enhanced.exe into the folder that holds SWOTL.EXE and the AC, CP, FE, FX and MIS folders.
2. Start SWOTL-Enhanced.exe.

On first start the program writes swotl-enhanced.ini next to the exe. All settings are in that file, each with a short explanation. When you start a new version for the first time, it rewrites the file in its own layout: your values stay as they are, new settings are added, and every setting gets its current explanation. The old file is kept as swotl-enhanced.ini.bak. Your own comments in the file are not carried over.

Keys added by SWOTL Enhanced

Key	Action
Alt+Enter or F11	Full screen on/off
Ctrl+F10	Release or capture the mouse
F12	Screenshot (swotlNNNN.bmp)
Ctrl+F11 / Ctrl+F12	Lower / raise the CPU speed limit
Ctrl+F9	Show speed, frame rate and CPU speed in the picture (they are always in the title bar)
Ctrl+F6	CRT shader on/off (saved in the ini file)
Ctrl+F7 / Ctrl+F8	Make the gamepad stick less / more curved (saved in the ini file)
Ctrl+F5	Start / stop a diagnostic recording (swotl-rec-NNNN.avi + .log, max 60 s)

All other keys go to the game. See SWOTL.DOC for the game's own keys.

Default gamepad layout

Gamepad	Game
Left stick	Joystick (in menus: mouse pointer)
A	Fire button 1 (in menus: click)
B	Fire button 2
X	Enter (drop bombs / rockets)
Y (hold)	Look back
Right stick	Look around (keypad views)
RT / LT	Throttle up / down
RB / LB	Rudder right / left (needs advanced=1)
D-pad	Flaps (up), gear (down), map (left), gun camera (right)
Start	Pause (Alt+P)
Back	Esc

You can change every button in the [gamepad] section of the ini file.

Rudder. SWOTL has a rudder only with advanced flight controls: set advanced=1 in [game]. Without it the rudder keys (F5-F9) do nothing, and a message in the window says so. LB and RB give full rudder while held and centre it when released. For an analog rudder on the triggers, set lt=RUDDER and rt=RUDDER, and move the throttle to the bumpers with lb=MINUS and rb=PLUS. The game itself only knows partial and full rudder, so SWOTL Enhanced turns the trigger into rudder key presses: a slight pull gives partial rudder, a further pull switches between centre and full rudder ten times a second in the ratio of the pull, and a full pull gives full rudder. In a P-51B over 6 seconds, a 15% pull turns about 4 degrees, 50% about 35 and a full pull about 76. Triggers can also take KEY1/KEY2 (held like a button, e.g. lt=F5/F9).

Stick response. By default the left stick is linear, just like a joystick from 1991. stick_curve (1.0 to 3.0) bends the response: small movements around the centre give finer control, and full stick still gives full deflection. Try 1.5 to 2.0. stick_range (0.3 to 1.0) limits the maximum deflection. Ctrl+F7 / Ctrl+F8 change the curve in steps of 0.25 while you fly.

Diagnostic recording. Ctrl+F5 records the game picture (320x200, 30 fps, uncompressed AVI) to swotl-rec-NNNN.avi in the game folder. The top-left corner of the picture shows the input state. A .log file next to it lists, for each frame, the timing (speed, fps, CPU speed), the keys and the stick values sent to the game. A recording of 20 seconds is about 115 MB.

CRT shader

SWOTL Enhanced uses the CRT shaders of DOSBox Staging 0.83.0 and chooses between them in the same way as its shader = crt-auto setting does for VGA games. A real VGA monitor drew every line of the 320x200 picture twice (double scanning), so a convincing scanline effect needs at least two to three screen pixels per line. The variant therefore depends on the height of the picture:

Height available for the picture	Variant
1600 pixels and more (4K screens)	crt-hyllian, VGA 4K preset
1200 to 1599 pixels (1440p screens)	crt-hyllian, VGA 1440p preset
800 to 1199 pixels (1080p screens)	vga-1080p-fake-double-scan
less than 800 pixels	no CRT effect, plain scale

As in DOSBox Staging, the picture is scaled in whole or half steps where that gives cleaner scanlines, and the colours are adjusted to those of a VGA monitor (P22 phosphors, 7800 K white point). When the window changes size, the variant can change; a short message shows the new one. shader=crt-1080p, crt-1440p or crt-4k forces one variant. shader=none switches the effect off. Ctrl+F6 switches between crt-auto and none.

The shaders need OpenGL 3.3, which every PC graphics card from the last 15 years supports. If OpenGL does not work, the program falls back to its normal renderer without the effect, and writes the reason to swotl-enhanced-gl.log. renderer=sdl always uses the normal renderer.

Settings (swotl-enhanced.ini)

• mips: the highest emulated CPU speed. The default is 40. About 20 is a fast 486. More speed gives a smoother 3D view.
• detail: ground detail, 1 to 5.
• advanced: advanced flight controls (rudder).
• joystick: auto, on or off. With auto, the game's joystick is on when a gamepad is connected or keyboard_flight=stick. With off, the arrow keys always work as classic keys.
• sound: 1/adlib, sb or 0. SWOTL only uses the FM (AdLib) part of a Sound Blaster: with the SB setting it writes to the same OPL2 ports and uses no digital sound. Both settings therefore sound exactly the same.
• volume
• shader: crt-auto (default), crt-1080p, crt-1440p, crt-4k or none.
• renderer: opengl (default, needed for the shader) or sdl.
• scale, aspect, integer, fullscreen, width, height. scale and integer apply when no CRT shader is active.
• mouse_speed
• keyboard_flight: stick (default) or classic. See Keyboard flying above. keyboard_stick_ramp and keyboard_stick_return set the seconds to full deflection and back to the centre.
• key_repeat_rate, key_repeat_delay: the key repeat while a key is held. The defaults are 30 per second and 250 ms.
• show_fps

Building from source

The release build is cross-compiled on Linux with clang, lld, mingw-w64 (built from source) and a static SDL3 3.2. See build.sh. The tools/ folder has a headless test runner and a test harness for the CPU core. The CPU core passes the SingleStepTests 8088 suite, apart from deliberate 286-style behaviour.

Licences

• SWOTL Enhanced source code: GPL-3.0-or-later, (c) 2026 Zwarteziel. See LICENSE.
• Nuked-OPL3 (third_party/opl3.c, opl3.h): LGPL-2.1-or-later, (c) Nuke.YKT. See third_party/LICENSE.Nuked-OPL3.
• CRT shaders and image adjustments (third_party/dosbox-staging-shaders): MIT, (c) The DOSBox Staging Team, Hyllian, Tyrells and others. See the README in that folder.
• SDL3 (linked statically in the Windows build): zlib licence.
• 8x8 BIOS font (src/font8x8.inc): derived from font8x8 by Daniel Hepper (public domain).
• Secret Weapons of the Luftwaffe is (c) Lucasfilm Games / LucasArts. No game files are included.