sacred_k/src/mods/borderless.cpp

// Borderless fullscreen.
//
// The game renders at a fixed resolution (1024x768). Unmodified, windowed mode
// shows that as a 1024x768 popup centred on the desktop; fullscreen mode
// switches the display mode. With this mod the game always runs windowed, the
// popup covers the whole monitor (mods/monitor.h: the preferred one), and each frame is scaled up into the largest
// centred rectangle with the game's aspect ratio (black bars elsewhere).
//
// Mouse positions are mapped back from that rectangle to game pixels, both in
// GetMouseClientPos (polled by the game) and in mouse window messages.
//
// sacredK.ini:
//   [borderless]
//   Enabled=1        ; 0 = original behaviour
//   IntegerScale=0   ; 1 = scale by whole multiples only (sharper, larger bars)
//   RunInBackground=1 ; keep the game running when it loses focus
//
// Vanilla pauses when the window loses focus (WM_ACTIVATEAPP sets bit 0x20000 in
// 0x0182cdb8 and pauses sound) and stops presenting; a monitor-sized window then
// goes black. With RunInBackground the deactivation is never passed to the
// game. Because the game polls the keyboard with GetAsyncKeyState, which sees
// keys pressed in any application, key state is hidden from it while another
// window has the focus.
//
// Known gap: one code path (0x00610650, cursor nudging) moves the cursor with
// SetCursorPos by a game-pixel delta, which is not scaled to screen pixels.

#include <algorithm>
#include <atomic>

#include <windows.h>
#include <windowsx.h>

#include "game/engine/input.h"
#include "game/render/dx_driver7.h"
#include "mods/hud.h"
#include "mods/input.h"
#include "mods/monitor.h"
#include "mods/widescreen.h"
#include "re/config.h"
#include "game/addresses.h"
#include "re/hook.h"
#include "re/log.h"

namespace {

// Where a gameWidth x gameHeight image appears in the window.
struct Layout {
    int gameWidth = 0;
    int gameHeight = 0;
    RECT client = {};  // scaled game image, window client coordinates
    RECT screen = {};  // same rectangle, screen coordinates
};

struct Viewport {
    bool active = false;
    HWND window = nullptr;
    bool runInBackground = false;
    Layout full;  // the whole back buffer
};

Viewport g_viewport;

const Layout& CurrentLayout() {
    return g_viewport.full;
}

bool Enabled() {
    return re::ConfigInt("borderless", "Enabled", 1) != 0;
}

// Largest rectangle with the game's aspect ratio that fits the monitor.
RECT FitRect(int areaWidth, int areaHeight, int width, int height, bool integerScale) {
    int scaledWidth;
    int scaledHeight;
    if (integerScale) {
        int scale = std::max(1, std::min(areaWidth / width, areaHeight / height));
        scaledWidth = width * scale;
        scaledHeight = height * scale;
    } else if (static_cast<long long>(areaWidth) * height > static_cast<long long>(areaHeight) * width) {
        scaledHeight = areaHeight;
        scaledWidth = MulDiv(width, areaHeight, height);
    } else {
        scaledWidth = areaWidth;
        scaledHeight = MulDiv(height, areaWidth, width);
    }
    int left = (areaWidth - scaledWidth) / 2;
    int top = (areaHeight - scaledHeight) / 2;
    return {left, top, left + scaledWidth, top + scaledHeight};
}

void ApplyBorderless(game::DxDriver7* driver) {
    HWND window = driver->window;
    const RECT area = mods::monitor::GameMonitorRect();
    const int areaWidth = area.right - area.left;
    const int areaHeight = area.bottom - area.top;

    SetWindowLongW(window, GWL_STYLE, WS_POPUP | WS_VISIBLE);
    SetWindowPos(window, HWND_TOP, area.left, area.top, areaWidth, areaHeight, SWP_FRAMECHANGED | SWP_SHOWWINDOW);

    const bool integerScale = re::ConfigInt("borderless", "IntegerScale", 0) != 0;
    auto makeLayout = [&](int width, int height) {
        Layout layout;
        layout.gameWidth = width;
        layout.gameHeight = height;
        layout.client = FitRect(areaWidth, areaHeight, width, height, integerScale);
        layout.screen = layout.client;
        OffsetRect(&layout.screen, area.left, area.top);
        return layout;
    };

    Viewport viewport;
    viewport.window = window;
    viewport.runInBackground = re::ConfigInt("borderless", "RunInBackground", 1) != 0;
    viewport.full = makeLayout(driver->mode.width, driver->mode.height);
    viewport.active = true;
    g_viewport = viewport;

    // Paint the bars: the window class background brush is black.
    InvalidateRect(window, nullptr, TRUE);

    const RECT& image = viewport.full.client;
    re::Log("borderless: %dx%d game -> %ldx%ld monitor, image at (%ld,%ld) %ldx%ld", viewport.full.gameWidth,
            viewport.full.gameHeight, static_cast<long>(areaWidth), static_cast<long>(areaHeight), image.left,
            image.top, image.right - image.left, image.bottom - image.top);
}

// Window client coordinates -> game pixels.
POINT ToGame(POINT p) {
    const Layout& layout = CurrentLayout();
    const int width = layout.client.right - layout.client.left;
    const int height = layout.client.bottom - layout.client.top;
    POINT result;
    result.x = std::clamp(MulDiv(p.x - layout.client.left, layout.gameWidth, width), 0, layout.gameWidth - 1);
    result.y = std::clamp(MulDiv(p.y - layout.client.top, layout.gameHeight, height), 0, layout.gameHeight - 1);
    result.x -= mods::hud::MenuFrameOffsetX();  // the main menu's centred frame
    return result;
}

// Fills everything except the game image with black.
void PaintBars(HDC dc) {
    RECT window;
    GetClientRect(g_viewport.window, &window);
    const RECT& image = CurrentLayout().client;
    const int saved = SaveDC(dc);
    ExcludeClipRect(dc, image.left, image.top, image.right, image.bottom);
    FillRect(dc, &window, static_cast<HBRUSH>(GetStockObject(BLACK_BRUSH)));
    RestoreDC(dc, saved);
}

bool IsMouseMessageWithClientCoords(UINT message) {
    // WM_MOUSEWHEEL and WM_MOUSEHWHEEL carry screen coordinates; leave them alone.
    return message >= WM_MOUSEFIRST && message <= WM_MOUSELAST && message != WM_MOUSEWHEEL &&
           message != WM_MOUSEHWHEEL;
}

} // namespace

namespace game {

RE_HOOK(addr::DxDriver7_SetDisplayMode, DxDriver7_SetDisplayMode);
RE_HOOK(addr::DxDriver7_Flip, DxDriver7_Flip);
RE_HOOK(addr::GetMouseClientPos, GetMouseClientPos);
RE_HOOK(addr::MainWindowProc, MainWindowProc);

int __fastcall DxDriver7_SetDisplayMode(DxDriver7* self, void* edx, void* deviceCaps, const DxDisplayMode* mode,
                                        uint32_t unknown) {
    if (!Enabled()) {
        return DxDriver7_SetDisplayMode_original(self, edx, deviceCaps, mode, unknown);
    }
    DxDisplayMode windowed = *mode;
    windowed.fullscreen = 0;
    mods::widescreen::ApplyRenderSize(windowed);
    g_viewport.active = false;
    const int result = DxDriver7_SetDisplayMode_original(self, edx, deviceCaps, &windowed, unknown);
    if (result) {
        ApplyBorderless(self);
    }
    return result;
}

int __fastcall DxDriver7_Flip(DxDriver7* self, void* edx) {
    // The original computes the blit rectangles once, for a centred window of
    // exactly the game's size; override them on every present.
    if (g_viewport.active && self->window == g_viewport.window) {
        const Layout& layout = CurrentLayout();
        self->blitSource = {0, 0, layout.gameWidth, layout.gameHeight};
        self->blitDest = layout.screen;
    }
    const int result = DxDriver7_Flip_original(self, edx);
    static std::atomic<int> failures = 0;
    if (result != 0 && failures++ < 5) {
        re::Log("borderless: present failed (0x%08x), source %ldx%ld -> dest (%ld,%ld)-(%ld,%ld)",
                static_cast<unsigned>(result), self->blitSource.right, self->blitSource.bottom, self->blitDest.left,
                self->blitDest.top, self->blitDest.right, self->blitDest.bottom);
    }
    return result;
}

void __cdecl GetMouseClientPos(HWND window, POINT* position) {
    GetMouseClientPos_original(window, position);
    if (window && g_viewport.active && window == g_viewport.window) {
        *position = ToGame(*position);
        position->x -= mods::hud::CursorOffsetX();
    }
}

LRESULT CALLBACK MainWindowProc(HWND window, UINT message, WPARAM wParam, LPARAM lParam) {
    if (mods::input::HandleWindowMessage(window, message, wParam, lParam)) {
        return 0;
    }
    if (!g_viewport.active || window != g_viewport.window) {
        return MainWindowProc_original(window, message, wParam, lParam);
    }

    if (IsMouseMessageWithClientCoords(message)) {
        POINT game = ToGame({GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam)});
        lParam = MAKELPARAM(game.x, game.y);
    }

    switch (message) {
    case WM_ERASEBKGND:
        PaintBars(reinterpret_cast<HDC>(wParam));
        return 1;

    case WM_ACTIVATEAPP:
        if (!wParam && g_viewport.runInBackground) {
            re::Log("borderless: focus lost, game keeps running");
            return 0;
        }
        break;
    }
    return MainWindowProc_original(window, message, wParam, lParam);
}

} // namespace game

// The game polls keys with GetAsyncKeyState, which reports keys pressed in any
// application. While it runs in the background, hide them from it.
SHORT WINAPI GetAsyncKeyStateWhenFocused(int key);
RE_HOOK_API(GetAsyncKeyState, GetAsyncKeyStateWhenFocused);

SHORT WINAPI GetAsyncKeyStateWhenFocused(int key) {
    if (g_viewport.active && g_viewport.runInBackground && GetForegroundWindow() != g_viewport.window) {
        return 0;
    }
    return GetAsyncKeyStateWhenFocused_original(key);
}

// The game's "bring the window to the front" (0x810af0, thiscall (window,
// timeout ms), ret 8; WinMain calls it three times): ShowWindow, then
// SetForegroundWindow until the window is in front and SetFocus until it has
// the focus. WinMain passes 0xffffffff, which never times out. Windows refuses
// the foreground to a process when the user clicked or typed elsewhere while
// it started, so the game hung at startup (2026-10-20, four times; main
// thread in this loop, log ending at WM_ACTIVATEAPP(1, 0)). Now it asks for a
// limited time, with the input of the window in front attached (which Windows
// allows), and carries on in the background otherwise; a click brings it up.
constexpr DWORD kForegroundWaitMs = 2000;

bool __fastcall BringWindowToFront(void* self, void* edx, HWND window, DWORD timeout);
RE_HOOK(0x00810af0, BringWindowToFront);
bool __fastcall BringWindowToFront(void*, void*, HWND window, DWORD timeout) {
    ShowWindow(window, SW_SHOW);
    const DWORD wait = std::min(timeout, kForegroundWaitMs);
    const DWORD start = GetTickCount();
    while (GetForegroundWindow() != window && GetTickCount() - start < wait) {
        const DWORD front = GetWindowThreadProcessId(GetForegroundWindow(), nullptr);
        const DWORD self = GetCurrentThreadId();
        const bool attached = front && front != self && AttachThreadInput(front, self, TRUE);
        BringWindowToTop(window);
        SetForegroundWindow(window);
        if (attached) {
            AttachThreadInput(front, self, FALSE);
        }
        Sleep(10);
    }
    const bool inFront = GetForegroundWindow() == window;
    if (inFront) {
        SetFocus(window);
    } else {
        re::Log("borderless: the game window did not get to the front, starting in the background");
    }
    UpdateWindow(window);
    return inFront;
}