# Borderless fullscreen

Request (2026-10-31): make the game start without crashing, then borderless
fullscreen as the first feature.

## The start-up crash

Measured 2026-10-31 (3440x1440, options `video.fullscreen = 1`):

- Started through the launcher from a background process, Windows doesn't
  hand the game window the foreground. In exclusive fullscreen Direct3D then
  minimises it (style gains `WS_MINIMIZE` after ~8 s, during "SETUP AI..." on
  the loading screen), and the game quits ~20 s later. On the way out
  `s2logicai.dll`'s static destructors call a pure virtual function (a global
  allocator object at `0x101BF774` is already destroyed), the game's
  `s2_purecall()` handler (`sacred2.exe` 0x489ada) breaks into the debugger:
  exception 0x80000003 in KERNELBASE.
- Started with focus (or directly, unmodified), it reaches the main menu.
- `cDX9Base::flip` minimises the window and sets device flag 4 when Present
  returns `D3DERR_DEVICELOST`.

So the crash was exclusive fullscreen losing the focus; it is gone with
borderless.

## How the mod works (`src/mods/borderless.cpp`)

`cDX9Base::_initDX(const sInitParams&)` (s2render 0x1029a736, exported, the
only device set-up, reached through `initDX` / `cDX9Advance::initAdvance`)
has a windowed path: style `0x12c00000`, size clamped to
`GetSystemMetrics(SM_CXSCREEN/SM_CYSCREEN)` minus the frame, window centred,
back buffer of that size, presentation interval default. See
`src/game/render/dx9base.h` for `sInitParams` and the addresses.

- The hook passes `fullscreen = 0` and the primary monitor's size.
- At startup the four uses of the style constant (0x1029ab49, ab56, ab5b,
  ab62) become `WS_POPUP | WS_VISIBLE`, so the game's own code makes a
  frameless window covering the monitor at (0,0).
- The launcher passes its foreground right to the game
  (`AllowSetForegroundWindow`).

Verified 2026-10-31 by automated runs: started without focus the game keeps
loading in the background; with focus it reaches the main menu, survives
switching to another window for 6 s and back, and quits cleanly on a close
request (no crash report, `MemLeaks_sacred2.xml` written).

## Consequences

- The resolution and fullscreen settings in Optionen no longer apply; the
  game always renders at the monitor's resolution.
- Always the primary monitor.
- In windowed mode the game presents with vsync (interval default); the
  options' vsync flag only applies to exclusive fullscreen.