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Prevent Windows borderless mode from taking exclusive fullscreen #347

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Merged
cybersecurity merged 1 commit into from
Oct 19, 2026
Merged

Prevent Windows borderless mode from taking exclusive fullscreen #347

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12 changes: 12 additions & 0 deletions port/linux/src/sdl_platform.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,10 @@ and the debug keyboard that the game's console reads.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef HALO_WINDOWS
/* port/windows/src/win32_window.c, compiled with the Windows SDK */
void win32_window_borderless_apply(SDL_Window *window);
#endif
#if !defined(_WIN32) && !defined(HALO_ANDROID)
#include <signal.h>
#endif
Expand Down Expand Up @@ -839,6 +843,9 @@ BOOL platform_video_initialize(unsigned long width, unsigned long height)
#endif
platform_fullscreen_requested = platform_fullscreen_setting();
platform_fullscreen_kind_apply();
#endif
#ifdef HALO_WINDOWS
win32_window_borderless_apply(platform_window);
#endif
platform_gl_context = SDL_GL_CreateContext(platform_window);
#ifdef HALO_GLES
Expand Down Expand Up @@ -950,6 +957,11 @@ void platform_video_swap(void)
static Uint64 next_frame;
Uint64 interval, now;

#endif
#ifdef HALO_WINDOWS
/* SDL can restore its fullscreen styles on a mode or focus change.
Keep borderless on the desktop before the driver presents a frame. */
win32_window_borderless_apply(platform_window);
#endif
SDL_GL_SwapWindow(platform_window);
#ifdef HALO_WEB
Expand Down
28 changes: 28 additions & 0 deletions port/windows/src/win32_window.c
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Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
/*
WIN32_WINDOW.C

Keep borderless OpenGL windows on the desktop. NVIDIA's driver treats
SDL's WS_POPUP fullscreen window as exclusive even without a display mode,
which blanks the monitor when the player switches to another application.
*/

#include <windows.h>
#include <SDL3/SDL.h>

void win32_window_borderless_apply(SDL_Window *window)
{
HWND handle;
LONG_PTR style;

if (!(SDL_GetWindowFlags(window) & SDL_WINDOW_FULLSCREEN) || SDL_GetWindowFullscreenMode(window))
return;
handle = SDL_GetPointerProperty(SDL_GetWindowProperties(window), SDL_PROP_WINDOW_WIN32_HWND_POINTER, NULL);
if (!handle)
return;
style = GetWindowLongPtr(handle, GWL_STYLE);
if (!(style & WS_POPUP) && !(GetWindowLongPtr(handle, GWL_EXSTYLE) & WS_EX_TOPMOST))
return;
SetWindowLongPtr(handle, GWL_STYLE, style & ~WS_POPUP);
SetWindowPos(handle, HWND_NOTOPMOST, 0, 0, 0, 0,
SWP_NOMOVE | SWP_NOSIZE | SWP_NOACTIVATE | SWP_FRAMECHANGED);
}