windows-nt/Source/XPSP1/NT/windows/appcompat/shims/layer/hidedisplaymodes.cpp

/*++

 Copyright (c) 2000 Microsoft Corporation

 Module Name:

    RestrictDisplayModes.cpp

 Abstract:

    Restrict the mode list enumerated by EnumDisplaySettings. This shim was 
    built for an application that enumerated only 10 modes and was hoping to 
    find 800x600 in that list. However, other applications that have fixed 
    size buffers for mode tables may also find this shim useful.

 Notes:

    This is a general purpose shim.

 History:

    05/05/2000 linstev  Created

--*/

#include "precomp.h"

IMPLEMENT_SHIM_BEGIN(HideDisplayModes)
#include "ShimHookMacro.h"


APIHOOK_ENUM_BEGIN
    APIHOOK_ENUM_ENTRY(EnumDisplaySettingsA)
    APIHOOK_ENUM_ENTRY(EnumDisplaySettingsW)
APIHOOK_ENUM_END

//
// Data needed in mode table
//

typedef struct _MODE
{
    DWORD dmBitsPerPel;
    DWORD dmPelsWidth;
    DWORD dmPelsHeight;
    DWORD dmDisplayFlags;
    DWORD dmDisplayFrequency;
    DWORD dwActualIndex;
    DWORD bIgnore;
} MODE;

// Permanent mode table
MODE* g_pModeTable = NULL;

// Number of entries in the mode table
DWORD g_dwCount = 0;

// Build the mode table on first call
BOOL g_bInit = FALSE;
void BuildModeList(void);

/*++

 Lookup from the sanitized mode table.

--*/

BOOL 
APIHOOK(EnumDisplaySettingsA)(
    LPCSTR     lpszDeviceName,
    DWORD      iModeNum,
    LPDEVMODEA lpDevMode
    )
{
    BuildModeList();
    
    BOOL bRet = FALSE;

    if (lpszDeviceName || ((LONG)iModeNum < 0) || !g_pModeTable) {
        bRet = ORIGINAL_API(EnumDisplaySettingsA)(
                                lpszDeviceName,
                                iModeNum,
                                lpDevMode);
    } else if (iModeNum < g_dwCount) {
        MODE* pmode = g_pModeTable + iModeNum;

        bRet = ORIGINAL_API(EnumDisplaySettingsA)(
                                lpszDeviceName,
                                pmode->dwActualIndex,
                                lpDevMode);

        if (bRet) {
            LOGN(
                eDbgLevelError,
                "[EnumDisplaySettingsA] Returning shorter list of display modes.");
            
            lpDevMode->dmBitsPerPel = pmode->dmBitsPerPel;
            lpDevMode->dmPelsWidth = pmode->dmPelsWidth;
            lpDevMode->dmPelsHeight = pmode->dmPelsHeight;
            lpDevMode->dmDisplayFlags = pmode->dmDisplayFlags;
            lpDevMode->dmDisplayFrequency = pmode->dmDisplayFrequency;
        }
    }

    return bRet;
}

/*++

 Lookup from the sanitized mode table.

--*/

BOOL 
APIHOOK(EnumDisplaySettingsW)(
    LPCWSTR    lpszDeviceName,
    DWORD      iModeNum,
    LPDEVMODEW lpDevMode
    )
{
    BuildModeList();
    
    BOOL bRet = FALSE;

    if (lpszDeviceName || ((LONG)iModeNum < 0) || !g_pModeTable) {
        bRet = ORIGINAL_API(EnumDisplaySettingsW)(
                                lpszDeviceName,
                                iModeNum,
                                lpDevMode);
    } else if (iModeNum < g_dwCount) {
        MODE* pmode = g_pModeTable + iModeNum;

        bRet = ORIGINAL_API(EnumDisplaySettingsW)(
                                lpszDeviceName,
                                pmode->dwActualIndex,
                                lpDevMode);

        if (bRet) {
            LOGN(
                eDbgLevelError,
                "[EnumDisplaySettingsW] Returning shorter list of display modes.");
            
            lpDevMode->dmBitsPerPel = pmode->dmBitsPerPel;
            lpDevMode->dmPelsWidth = pmode->dmPelsWidth;
            lpDevMode->dmPelsHeight = pmode->dmPelsHeight;
            lpDevMode->dmDisplayFlags = pmode->dmDisplayFlags;
            lpDevMode->dmDisplayFrequency = pmode->dmDisplayFrequency;
        }
    }

    return bRet;
}

/*++

 Sort the table by Width+Height+BitsPerPel+Frequency in that order so that 
 they can be easily filtered.

--*/

int 
_cdecl
compare1(
    const void* a1,
    const void* a2
    )
{
    MODE* arg1 = (MODE*)a1;
    MODE* arg2 = (MODE*)a2;

    int d;

    d = arg1->dmPelsWidth - arg2->dmPelsWidth;

    if (d == 0) {
        d = arg1->dmPelsHeight - arg2->dmPelsHeight;
    }

    if (d == 0) {
        d = arg1->dmBitsPerPel - arg2->dmBitsPerPel;
    }

    if (d == 0) {
        d = arg1->dmDisplayFrequency - arg2->dmDisplayFrequency;
    }

    return d;
}

/*++

 Sort the table so it looks like a Win9x mode table, i.e. BitsPerPel is the
 primary sort key.

--*/

int 
_cdecl
compare2(
    const void* a1,
    const void* a2
    )
{
    MODE* arg1 = (MODE*)a1;
    MODE* arg2 = (MODE*)a2;

    int d;

    d = arg1->dmBitsPerPel - arg2->dmBitsPerPel;

    if (d == 0) {
        d = arg1->dmPelsWidth - arg2->dmPelsWidth;
    }

    if (d == 0) {
        d = arg1->dmPelsHeight - arg2->dmPelsHeight;
    }

    if (d == 0) {
        d = arg1->dmDisplayFrequency - arg2->dmDisplayFrequency;
    }

    return d;
}

/*++

 Create a new mode table based upon the sanitized existing table. To do this, 
 we do the following:
 
    1. Get the entire table
    2. Sort it - to allow efficient removal of duplicates
    3. Remove duplicates and unwanted modes
    4. Build a new table with only the modes that 'pass'

--*/

void
BuildModeList(
    void
    )
{
    if (g_bInit) {
        return;
    }

    DEVMODEA dm;
    ULONG    i, j;
    
    dm.dmSize = sizeof(DEVMODEA);

    //
    // Figure out how many modes there are.
    //

    i = 0;
    
    while (EnumDisplaySettingsA(NULL, i, &dm)) {
        i++;
    }

    //
    // Allocate the full mode table.
    //
    MODE* pTempTable = (MODE*)malloc(sizeof(MODE) * i);
    
    if (!pTempTable) {
        LOGN(
            eDbgLevelError,
            "[BuildModeList] Failed to allocate %d bytes.",
            sizeof(MODE) * i);
        
        return;
    }

    MODE* pmode = pTempTable;

    //
    // Get all the modes.
    //
    i = 0;
    
    while (EnumDisplaySettingsA(NULL, i, &dm)) {
        pmode->dmBitsPerPel       = dm.dmBitsPerPel;
        pmode->dmPelsWidth        = dm.dmPelsWidth;
        pmode->dmPelsHeight       = dm.dmPelsHeight;
        pmode->dmDisplayFlags     = dm.dmDisplayFlags;
        pmode->dmDisplayFrequency = 0; // dm.dmDisplayFrequency;
        pmode->dwActualIndex      = i;
        pmode->bIgnore            = FALSE;

        pmode++;
        i++;
    }
    
    //
    // Sort the full table so we can remove duplicates easily.
    //
    qsort((void*)pTempTable, (size_t)i, sizeof(MODE), compare1);

    //
    // Strip away bad modes by setting them as ignored.
    //
    pmode = pTempTable;
    
    MODE* pprev = NULL;

    for (j = 0; j < i; j++) {
        if ((pmode->dmBitsPerPel < 8) || 
            (pmode->dmPelsWidth < 640) ||
            (pmode->dmPelsHeight < 480) ||
            (pmode->dmPelsWidth > 1280) || 
            (pprev &&
            (pprev->dmBitsPerPel == pmode->dmBitsPerPel) &&
            (pprev->dmPelsWidth == pmode->dmPelsWidth) &&
            (pprev->dmPelsHeight == pmode->dmPelsHeight))) {
            
            //
            // Special-case 640x480x4bit.
            //
            if ((pmode->dmBitsPerPel == 4) && 
                (pmode->dmPelsWidth == 640) &&
                (pmode->dmPelsHeight == 480)) {
                
                g_dwCount++;
            } else {
                pmode->bIgnore = TRUE;
            }
        } else {
            g_dwCount++;
        }

        pprev = pmode;
        pmode++;
        
    }

    //
    // Build the new table with only the modes that passed.
    //
    g_pModeTable = (MODE*)malloc(sizeof(MODE) * g_dwCount);
    
    if (!g_pModeTable) {
        LOGN(
            eDbgLevelError,
            "[BuildModeList] Failed to allocate %d bytes.",
            sizeof(MODE) * g_dwCount);
        
        free(pTempTable);
        return;
    }

    MODE* pmoden = g_pModeTable;
    
    pmode = pTempTable;

    for (j = 0; j < i; j++) {
        if (!pmode->bIgnore) {
            MoveMemory(pmoden, pmode, sizeof(MODE));
            pmoden++;
        }
        pmode++;
    }

    //
    // Sort the full table so we can remove duplicates easily.
    //
    qsort((void*)g_pModeTable, (size_t)g_dwCount, sizeof(MODE), compare2);

    free(pTempTable);

    g_bInit = TRUE;
}

/*++

 Register hooked functions

--*/

HOOK_BEGIN

    APIHOOK_ENTRY(USER32.DLL, EnumDisplaySettingsA)
    APIHOOK_ENTRY(USER32.DLL, EnumDisplaySettingsW)

HOOK_END


IMPLEMENT_SHIM_END