我在一两天前已经问过一个非常类似的问题,但是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,并进行以下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;
}


我不了解WinAPI,但是我在Viual Studio中看到,每次调用ScreenCapture()时,都有未释放的RAM,这是一个问题。

如果你们当中有些人知道错误在哪里...

感谢帮助,谢谢:)

最佳答案

HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);


GetDC(0)必须用ReleasedDC清除。以这种方式编写GetDC(0)时,将无法清除。您的程序只有10,000个GDI句柄,因此此资源泄漏可能是一个严重的问题。

您应该改为:

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


HWND_DESKTOP只是0,为了清楚起见,我使用了它。 GetDC返回一个句柄hdc_desktop,该句柄可以在最后清理。

DeleteObject(hBmp)是一个小错误,因为hBmp当前在hDc中被选中并且无法删除。许多程序员都犯了这个错误,所以新的Windows版本(我认为自XP以来)就已经出现了这种情况,因此Windows修复了该错误(至少在这种情况下),但是您应该确实保存旧位图的句柄,还原旧的位图,然后删除新的位图。

GetDIBits还有另一个小错误。文档说,调用该函数时,不得将hbitmap选中到dc中。但是,Windows再次可以看到此错误并进行修复。

您的SaveBMPFile可以简化。您没有保存调色板位图,可以完全忽略调色板。

未解决的问题:您正在使用Unicode函数,因此您使用UTF-16字符串文字:L"screenshot.bmp"而不是"screenshot.bmp"

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;
}


您可以循环运行此程序,并在Taskman中观察GDI手柄,以确保没有泄漏。

关于c - 屏幕截图WinAPI-可用内存,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/45900876/

10-12 16:14