C 屏幕截图WinAPI-可用内存

一两天前我已经问了一个非常类似的问题，但我的问题不是很清楚，所以我尝试在这里重新表述：

我想做一个屏幕截图，为此我搜索并找到以下代码：

#include <windows.h>
#include <stdio.h>

inline int GetFilePointer(HANDLE FileHandle)
{
    return SetFilePointer(FileHandle, 0, 0, FILE_CURRENT);
}

extern _Bool SaveBMPFile(char* filePath, HBITMAP bitmap, HDC bitmapDC, int width, int height)
{
    _Bool Success = 0;
    HDC SurfDC = NULL;        // GDI-compatible device context for the surface
    HBITMAP OffscrBmp = NULL; // bitmap that is converted to a DIB
    HDC OffscrDC = NULL;      // offscreen DC that we can select OffscrBmp into
    LPBITMAPINFO lpbi = NULL; // bitmap format info; used by GetDIBits
    LPVOID lpvBits = NULL;    // pointer to bitmap bits array
    HANDLE BmpFile = INVALID_HANDLE_VALUE;    // destination .bmp file
    BITMAPFILEHEADER bmfh;  // .bmp file header

                            // We need an HBITMAP to convert it to a DIB:
    if ((OffscrBmp = CreateCompatibleBitmap(bitmapDC, width, height)) == NULL)
        return 0;

    // The bitmap is empty, so let's copy the contents of the surface to it.
    // For that we need to select it into a device context. We create one.
    if ((OffscrDC = CreateCompatibleDC(bitmapDC)) == NULL)
        return 0;

    // Select OffscrBmp into OffscrDC:
    HBITMAP OldBmp = (HBITMAP)SelectObject(OffscrDC, OffscrBmp);

    // Now we can copy the contents of the surface to the offscreen bitmap:
    BitBlt(OffscrDC, 0, 0, width, height, bitmapDC, 0, 0, SRCCOPY);

    // GetDIBits requires format info about the bitmap. We can have GetDIBits
    // fill a structure with that info if we pass a NULL pointer for lpvBits:
    // Reserve memory for bitmap info (BITMAPINFOHEADER + largest possible
    // palette):
    if ((lpbi = (LPBITMAPINFO)malloc(sizeof(BITMAPINFOHEADER) + 256 * sizeof(RGBQUAD))) == NULL)
        return 0;


    ZeroMemory(&lpbi->bmiHeader, sizeof(BITMAPINFOHEADER));
    lpbi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    // Get info but first de-select OffscrBmp because GetDIBits requires it:
    SelectObject(OffscrDC, OldBmp);
    if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, NULL, lpbi, DIB_RGB_COLORS))
        return 0;

    // Reserve memory for bitmap bits:
    if ((lpvBits = malloc(lpbi->bmiHeader.biSizeImage)) == NULL)
        return 0;

    // Have GetDIBits convert OffscrBmp to a DIB (device-independent bitmap):
    if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, lpvBits, lpbi, DIB_RGB_COLORS))
        return 0;


    //ANSI->Unicode
    LPCSTR szAnsi = filePath;
    int Size = MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, NULL, 0);
    LPWSTR filename = malloc(sizeof(LPWSTR) * Size);
    MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, filename, Size);
    // Create a file to save the DIB to:
    if ((BmpFile = CreateFile(filename,
        GENERIC_WRITE,
        0, NULL,
        CREATE_ALWAYS,
        FILE_ATTRIBUTE_NORMAL,
        NULL)) == INVALID_HANDLE_VALUE)

        return 0;

    DWORD Written;    // number of bytes written by WriteFile

                      // Write a file header to the file:
    bmfh.bfType = 19778;        // 'BM'
                                // bmfh.bfSize = ???        // we'll write that later
    bmfh.bfReserved1 = bmfh.bfReserved2 = 0;
    // bmfh.bfOffBits = ???     // we'll write that later
    if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
        return 0;

    if (Written < sizeof(bmfh))
        return 0;

    // Write BITMAPINFOHEADER to the file:
    if (!WriteFile(BmpFile, &lpbi->bmiHeader, sizeof(BITMAPINFOHEADER), &Written, NULL))
        return 0;

    if (Written < sizeof(BITMAPINFOHEADER))
        return 0;

    // Calculate size of palette:
    int PalEntries;
    // 16-bit or 32-bit bitmaps require bit masks:
    if (lpbi->bmiHeader.biCompression == BI_BITFIELDS)
        PalEntries = 3;
    else
        // bitmap is palettized?
        PalEntries = (lpbi->bmiHeader.biBitCount <= 8) ?
        // 2^biBitCount palette entries max.:
        (int)(1 << lpbi->bmiHeader.biBitCount)
        // bitmap is TrueColor -> no palette:
        : 0;
    // If biClrUsed use only biClrUsed palette entries:
    if (lpbi->bmiHeader.biClrUsed)
        PalEntries = lpbi->bmiHeader.biClrUsed;

    // Write palette to the file:
    if (PalEntries) {
        if (!WriteFile(BmpFile, &lpbi->bmiColors, PalEntries * sizeof(RGBQUAD), &Written, NULL))
            return 0;

        if (Written < PalEntries * sizeof(RGBQUAD))
            return 0;
    }

    // The current position in the file (at the beginning of the bitmap bits)
    // will be saved to the BITMAPFILEHEADER:
    bmfh.bfOffBits = GetFilePointer(BmpFile);

    // Write bitmap bits to the file:
    if (!WriteFile(BmpFile, lpvBits, lpbi->bmiHeader.biSizeImage, &Written, NULL))
        return 0;

    if (Written < lpbi->bmiHeader.biSizeImage)
        return 0;

    // The current pos. in the file is the final file size and will be saved:
    bmfh.bfSize = GetFilePointer(BmpFile);

    // We have all the info for the file header. Save the updated version:
    SetFilePointer(BmpFile, 0, 0, FILE_BEGIN);
    if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
        return 0;

    if (Written < sizeof(bmfh))
        return 0;

    return 1;
}



_Bool ScreenCapture(char* filePath, int xStart, int yStart, int width, int height)
{
    // get a DC compat. w/ the screen
    HDC hDc = CreateCompatibleDC(0);

    // make a bmp in memory to store the capture in
    HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);

    // join em up
    SelectObject(hDc, hBmp);

    // copy from the screen to my bitmap
    BitBlt(hDc, 0, 0, width, height, GetDC(0), xStart, yStart, SRCCOPY);

    // save my bitmap
    _Bool ret = SaveBMPFile(filePath, hBmp, hDc, width, height);

    // free the bitmap memory
    DeleteObject(hBmp);

    return ret;
}

main()
{
    ScreenCapture("screenshot.bmp", 0, 0, 1920, 1080);

    FILE* Screen = NULL;
    Screen = fopen("screenshot.bmp", "r"); //Error, the image is "used" somewhere...     

    return 0;
}

#包括
#包括
内联int GetFilePointer（句柄FileHandle）
{
返回SetFilePointer（文件句柄，0，0，当前文件）；
}
extern\u Bool SaveBMPFile（字符*文件路径、HBITMAP位图、HDC位图、整数宽度、整数高度）
{
_布尔成功=0；
HDC SurfDC=NULL；//曲面的GDI兼容设备上下文
HBITMAP OffscrBmp=NULL；//转换为DIB的位图
HDC OffscrDC=NULL；//我们可以选择OffscrBmp进入的屏幕外DC
LPBITMAPINFO lpbi=NULL；//位图格式信息；由GetDIBits使用
LPVOID lpvBits=NULL；//指向位图位数组的指针
HANDLE BmpFile=无效的\u HANDLE\u值；//destination.bmp文件
BITMAPFILEHEADER bmfh；//.bmp文件头
//我们需要HBITMAP将其转换为DIB：
if（（OffscrBmp=CreateCompatibleBitmap（位图、宽度、高度））==NULL）
返回0；
//位图是空的，所以让我们将曲面的内容复制到它。
//为此，我们需要将其选择到设备上下文中。我们创建一个。
if（（OffscrDC=CreateCompatibleDC（bitmapDC））==NULL）
返回0；
//将OffscrBmp选择到OffscrDC中：
HBITMAP OldBmp=（HBITMAP）选择对象（OffscrDC，OffscrBmp）；
//现在，我们可以将曲面的内容复制到屏幕外位图：
BitBlt（OffscrDC，0，0，宽度，高度，bitmapDC，0，0，SRCCOPY）；
//GetDIBits需要有关位图的格式信息。我们可以使用GetDIBits
//如果我们为lpvBits传递空指针，则用该信息填充结构：
//为位图信息保留内存（BitMapInfo头+最大值）
//调色板）：
if（（lpbi=（LPBITMAPINFO）malloc（sizeof（BitMapInfo头）+256*sizeof（RGBQUAD））==NULL）
返回0；
零内存（&lpbi->bmiHeader，sizeof（BitMapInfo头））；
lpbi->bmiHeader.biSize=sizeof（BitMapInfo头文件）；
//获取信息，但首先取消选择OffscrBmp，因为GetDIBits需要它：
选择对象（OffscrDC、OldBmp）；
if（！GetDIBits（OffscrDC、OffscrBmp、0、高度、NULL、lpbi、DIB_RGB_颜色））
返回0；
//为位图位保留内存：
if（（lpvBits=malloc（lpbi->bmiHeader.biSizeImage））==NULL）
返回0；
//让GetDIBits将OffscrBmp转换为DIB（独立于设备的位图）：
如果（！GetDIBits（OffscrDC、OffscrBmp、0、高度、lpvBits、lpbi、DIB_RGB_颜色））
返回0；
//ANSI->Unicode
LPCSTR szAnsi=文件路径；
int Size=MultiByteToWideChar（CP_ACP，0，szAnsi，-1，NULL，0）；
LPWSTR文件名=malloc（sizeof（LPWSTR）*大小）；
MultiByteToWideChar（CP_ACP，0，szAnsi，-1，文件名，大小）；
//创建要将DIB保存到的文件：
如果（（BmpFile=CreateFile）（文件名，
你写什么，
0，空，
永远创造你，
文件\u属性\u正常，
NULL））==无效的\u句柄\u值）
返回0；
DWORD WRITED；//WriteFile写入的字节数
//将文件头写入文件：
bmfh.bfType=19778；/“BM”
//bmfh.bfSize=？？？//我们稍后再写
bmfh.bfReserved1=bmfh.bfReserved2=0；
//bmfh.bfOffBits=？？？//我们稍后再写
if（！WriteFile（BmpFile，&bmfh，sizeof（bmfh），&writed，NULL））
返回0；
如果（书写bmiHeader，sizeof（BitMapInfo Header），&writed，NULL））
返回0；
if（写入bmiHeader.biCompression==BI\u位字段）
帕伦蒂斯=3；
其他的
//位图是调色板吗？
PalEntries=（lpbi->bmiHeader.biBitCount无调色板：
: 0;
//如果使用BICLRUSE，请仅使用BICLRUSE调色板条目：
if（lpbi->bmiHeader.biClrUsed）
PalEntries=lpbi->bmiHeader.biClrUsed；
//将调色板写入文件：
国际单项体育联合会（帕伦特里）{
如果（！WriteFile（BmpFile，&lpbi->bmiColors，PalEntries*sizeof（RGBQUAD），&writed，NULL））
返回0；
if（书面bmiHeader.biSizeImage，&writed，NULL））
返回0；
如果（写入bmiHeader.biSizeImage）
返回0；
//文件中的当前位置是最终文件大小，将保存：
bmfh.bfSize=GetFilePointer（BmpFile）；
//我们有文件头的所有信息。保存更新版本：
SetFilePointer（BmpFile，0，0，FILE_BEGIN）；
if（！WriteFile（BmpFile，&bmfh，sizeof（bmfh），&writed，NULL））
返回0；
如果（书写#include <windows.h>
#include <stdio.h>

// Helper function to retrieve current position of file pointer:
inline int GetFilePointer(HANDLE FileHandle)
{
    return SetFilePointer(FileHandle, 0, 0, FILE_CURRENT);
}
//---------------------------------------------------------------------------

// Screenshot
//    -> FileName: Name of file to save screenshot to
//    -> lpDDS: DirectDraw surface to capture
//    <- Result: Success
//
extern _Bool SaveBMPFile(char* filePath, HBITMAP bitmap, HDC bitmapDC, int width, int height)
{
    _Bool Success = 0;
    HBITMAP OffscrBmp = NULL; // bitmap that is converted to a DIB
    HDC OffscrDC = NULL;      // offscreen DC that we can select OffscrBmp into
    LPBITMAPINFO lpbi = NULL; // bitmap format info; used by GetDIBits
    LPVOID lpvBits = NULL;    // pointer to bitmap bits array
    HANDLE BmpFile = INVALID_HANDLE_VALUE;    // destination .bmp file
    BITMAPFILEHEADER bmfh;  // .bmp file header

                            // We need an HBITMAP to convert it to a DIB:
    if ((OffscrBmp = CreateCompatibleBitmap(bitmapDC, width, height)) == NULL)
        return 0;

    // The bitmap is empty, so let's copy the contents of the surface to it.
    // For that we need to select it into a device context. We create one.
    if ((OffscrDC = CreateCompatibleDC(bitmapDC)) == NULL)
        return 0;

    // Select OffscrBmp into OffscrDC:
    HBITMAP OldBmp = (HBITMAP)SelectObject(OffscrDC, OffscrBmp);

    // Now we can copy the contents of the surface to the offscreen bitmap:
    BitBlt(OffscrDC, 0, 0, width, height, bitmapDC, 0, 0, SRCCOPY);

    // GetDIBits requires format info about the bitmap. We can have GetDIBits
    // fill a structure with that info if we pass a NULL pointer for lpvBits:
    // Reserve memory for bitmap info (BITMAPINFOHEADER + largest possible
    // palette):
    if ((lpbi = (LPBITMAPINFO)malloc(sizeof(BITMAPINFOHEADER) + 256 * sizeof(RGBQUAD))) == NULL)
        return 0;


    ZeroMemory(&lpbi->bmiHeader, sizeof(BITMAPINFOHEADER));
    lpbi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    // Get info but first de-select OffscrBmp because GetDIBits requires it:
    SelectObject(OffscrDC, OldBmp);
    if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, NULL, lpbi, DIB_RGB_COLORS))
        return 0;

    // Reserve memory for bitmap bits:
    if ((lpvBits = malloc(lpbi->bmiHeader.biSizeImage)) == NULL)
        return 0;

    // Have GetDIBits convert OffscrBmp to a DIB (device-independent bitmap):
    if (!GetDIBits(OffscrDC, OffscrBmp, 0, height, lpvBits, lpbi, DIB_RGB_COLORS))
        return 0;


    //ANSI->Unicode
    LPCSTR szAnsi = filePath;
    int Size = MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, NULL, 0);
    LPWSTR filename = malloc(sizeof(LPWSTR) * Size);
    MultiByteToWideChar(CP_ACP, 0, szAnsi, -1, filename, Size);
    // Create a file to save the DIB to:
    if ((BmpFile = CreateFile(filename,
        GENERIC_WRITE,
        0, NULL,
        CREATE_ALWAYS,
        FILE_ATTRIBUTE_NORMAL,
        NULL)) == INVALID_HANDLE_VALUE)

        return 0;

    DWORD Written;    // number of bytes written by WriteFile

                      // Write a file header to the file:
    bmfh.bfType = 19778;        // 'BM'
                                // bmfh.bfSize = ???        // we'll write that later
    bmfh.bfReserved1 = bmfh.bfReserved2 = 0;
    // bmfh.bfOffBits = ???     // we'll write that later
    if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
        return 0;

    if (Written < sizeof(bmfh))
        return 0;

    // Write BITMAPINFOHEADER to the file:
    if (!WriteFile(BmpFile, &lpbi->bmiHeader, sizeof(BITMAPINFOHEADER), &Written, NULL))
        return 0;

    if (Written < sizeof(BITMAPINFOHEADER))
        return 0;

    // Calculate size of palette:
    int PalEntries;
    // 16-bit or 32-bit bitmaps require bit masks:
    if (lpbi->bmiHeader.biCompression == BI_BITFIELDS)
        PalEntries = 3;
    else
        // bitmap is palettized?
        PalEntries = (lpbi->bmiHeader.biBitCount <= 8) ?
        // 2^biBitCount palette entries max.:
        (int)(1 << lpbi->bmiHeader.biBitCount)
        // bitmap is TrueColor -> no palette:
        : 0;
    // If biClrUsed use only biClrUsed palette entries:
    if (lpbi->bmiHeader.biClrUsed)
        PalEntries = lpbi->bmiHeader.biClrUsed;

    // Write palette to the file:
    if (PalEntries) {
        if (!WriteFile(BmpFile, &lpbi->bmiColors, PalEntries * sizeof(RGBQUAD), &Written, NULL))
            return 0;

        if (Written < PalEntries * sizeof(RGBQUAD))
            return 0;
    }

    // The current position in the file (at the beginning of the bitmap bits)
    // will be saved to the BITMAPFILEHEADER:
    bmfh.bfOffBits = GetFilePointer(BmpFile);

    // Write bitmap bits to the file:
    if (!WriteFile(BmpFile, lpvBits, lpbi->bmiHeader.biSizeImage, &Written, NULL))
        return 0;

    if (Written < lpbi->bmiHeader.biSizeImage)
        return 0;

    // The current pos. in the file is the final file size and will be saved:
    bmfh.bfSize = GetFilePointer(BmpFile);

    // We have all the info for the file header. Save the updated version:
    SetFilePointer(BmpFile, 0, 0, FILE_BEGIN);
    if (!WriteFile(BmpFile, &bmfh, sizeof(bmfh), &Written, NULL))
        return 0;

    if (Written < sizeof(bmfh))
        return 0;

    DeleteObject(OffscrBmp);
    DeleteObject(OldBmp);
    DeleteDC(OffscrDC);
    CloseHandle(BmpFile);

    free(lpbi);
    free(lpvBits);
    free(filename);

    return 1;
}

_Bool ScreenCapture(char* filePath, int xStart, int yStart, int width, int height)
{
    // get a DC compat. w/ the screen
    HDC hDc = CreateCompatibleDC(0);

    // make a bmp in memory to store the capture in
    HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);

    // join em up
    SelectObject(hDc, hBmp);

    // copy from the screen to my bitmap
    BitBlt(hDc, 0, 0, width, height, GetDC(0), xStart, yStart, SRCCOPY);

    // save my bitmap
    _Bool ret = SaveBMPFile(filePath, hBmp, hDc, width, height);

    // free the bitmap memory
    DeleteObject(hBmp);
    DeleteDC(hDc);

    return ret;
}

main()
{
    ScreenCapture("screenshot.png", 0, 0, 1920, 1080);

    return 0;
}

HDC hdc_desktop = GetDC(HWND_DESKTOP);
HBITMAP hBmp = CreateCompatibleBitmap(hdc_desktop, width, height);
...
ReleaseDC(HWND_DESKTOP, hdc_desktop);

extern _Bool SaveBMPFile(const wchar_t* filePath, 
    HDC memdc, HBITMAP hbitmap, int width, int height)
{
    _Bool success = 0;
    WORD bpp = 24; //or 32 for 32-bit bitmap
    DWORD size = ((width * bpp + 31) / 32) * 4 * height;

    BITMAPFILEHEADER filehdr = { 0 };
    filehdr.bfType = 19778;
    filehdr.bfSize = 54 + size;
    filehdr.bfOffBits = 54; 
    //54 = 14 + 40, sizeof BITMAPFILEHEADER & BITMAPINFOHEADER

    BITMAPINFOHEADER infohdr = { sizeof(infohdr) };
    infohdr.biWidth = width;
    infohdr.biHeight = height;
    infohdr.biPlanes = 1;
    infohdr.biBitCount = bpp;

    BYTE *bits = malloc(size);
    GetDIBits(memdc, hbitmap, 0, height, bits, (BITMAPINFO*)&infohdr, DIB_RGB_COLORS);

    HANDLE hfile = CreateFileW(filePath,
        GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
    if(hfile != INVALID_HANDLE_VALUE)
    {
        DWORD temp;
        WriteFile(hfile, &filehdr, 14, &temp, NULL);
        WriteFile(hfile, &infohdr, 40, &temp, NULL);
        WriteFile(hfile, bits, size, &temp, NULL);
        CloseHandle(hfile);
        success = 1;
    }

    free(bits);    
    return success;
}

_Bool ScreenCapture(const wchar_t* filePath, int x, int y, int width, int height)
{
    HDC hdc = GetDC(HWND_DESKTOP);
    HDC memdc = CreateCompatibleDC(hdc);
    HBITMAP hbitmap = CreateCompatibleBitmap(hdc, width, height);
    HBITMAP oldbitmap = SelectObject(memdc, hbitmap);
    BitBlt(memdc, 0, 0, width, height, hdc, x, y, SRCCOPY);
    SelectObject(memdc, oldbitmap);

    _Bool ret = SaveBMPFile(filePath, memdc, hbitmap, width, height);

    DeleteObject(hbitmap);
    DeleteDC(memdc);
    ReleaseDC(HWND_DESKTOP, hdc);

    return ret;
}

int main(void)
{
    ScreenCapture(L"screenshot.bmp", 0, 0, 
        GetSystemMetrics(SM_CXFULLSCREEN), GetSystemMetrics(SM_CYFULLSCREEN));
    return 0;
}