c++ - 使用WinApi的C++中的多监视器屏幕截图仅2个监视器

我具有使用WinApi和C++在Windows平台上进行屏幕截图的功能。它可以完美地与一台和两台显示器配合使用，但是当我在一台具有3台或更多显示器的机器上运行时，它只能拍摄两台显示器的照片。

我认为我的难题是“主”监视器左侧的监视器内容被删减了。可悲的是，我不知道如何解决它或我做错了什么。

我已经读过有关BitBlt和StretchBlt的文章，所以我尝试了一下，但没有成功。

这就是我在做什么:

// Get the system metrics
const int width = GetSystemMetrics(SM_CXVIRTUALSCREEN);
const int height = GetSystemMetrics(SM_CYVIRTUALSCREEN);

宽度和高度可以为所有显示器完美计算。

// Create a normal DC and a memory DC for the entire screen. The normal DC provides a "snapshot" of the screen contents.
// The memory DC keeps a copy of this "snapshot" in the associated bitmap.
const HDC hdcScr = CreateDCW(TEXT("DISPLAY"), NULL, NULL, NULL);
const HDC hdcMem = CreateCompatibleDC(hdcScr);



if (!StretchBlt(hdcMem, 0, 0, width, height, hdcScr, 0, 0, width, height, SRCCOPY)) {
    return;
}


// Create a compatible bitmap for hdcScreen.
const HBITMAP hbmScr = CreateCompatibleBitmap(hdcScr, width, height);
if (hbmScr == 0) {
    return;
}

if (!BitBlt(hdcMem, 0, 0, width, height, hdcScr, 0, 0, SRCCOPY)) {
    return;
}



// Select the bitmaps into the compatible DC.
if (!SelectObject(hdcMem, hbmScr)) {
    DeleteDC(hdcScr);
    DeleteDC(hdcMem);
    DeleteObject(hbmScr);
    return;
}

// Copy color data for the entire display into a bitmap that is selected into a compatible DC.
if (!StretchBlt(hdcMem, 0, 0, width, height, hdcScr, 0, 0, width, height, SRCCOPY)) {
    DeleteDC(hdcScr);
    DeleteDC(hdcMem);
    DeleteObject(hbmScr);
    return;
}

BITMAP bmp;

// Retrieve the bitmap's color format, width, and height.
if (!GetObject(hbmScr, sizeof(BITMAP), reinterpret_cast<LPSTR>(&bmp))) {
    DeleteDC(hdcScr);
    DeleteDC(hdcMem);
    DeleteObject(hbmScr);
    return;
}


// Convert the color format to a count of bits.
unsigned short cClrBits = bmp.bmPlanes * bmp.bmBitsPixel;
if (cClrBits == 1) {
    cClrBits = 1;
}
else if (cClrBits <= 4) {
    cClrBits = 4;
}
else if (cClrBits <= 8) {
    cClrBits = 8;
}
else if (cClrBits <= 16) {
    cClrBits = 16;
}
else if (cClrBits <= 24) {
    cClrBits = 24;
}
else {
    cClrBits = 32;
}


PBITMAPINFO pbmi;

// Allocate memory for the BITMAPINFO structure. (This structure contains a BITMAPINFOHEADER structure and an array of RGBQUAD data structures.)
if (cClrBits != 24) {
    pbmi = static_cast<PBITMAPINFO>(LocalAlloc(LPTR, sizeof(BITMAPINFOHEADER) + sizeof(RGBQUAD) * (1 << cClrBits)));
}
else { // There is no RGBQUAD array for the 24-bit-per-pixel format.
    pbmi = static_cast<PBITMAPINFO>(LocalAlloc(LPTR, sizeof(BITMAPINFOHEADER)));
}

// Initialize the fields in the BITMAPINFO structure.
pbmi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
pbmi->bmiHeader.biWidth = bmp.bmWidth;
pbmi->bmiHeader.biHeight = bmp.bmHeight;
pbmi->bmiHeader.biPlanes = bmp.bmPlanes;
pbmi->bmiHeader.biBitCount = bmp.bmBitsPixel;

if (cClrBits < 24) {
    pbmi->bmiHeader.biClrUsed = (1 << cClrBits);
}

// If the bitmap is not compressed, set the BI_RGB flag.
pbmi->bmiHeader.biCompression = BI_RGB;

// Compute the number of bytes in the array of color indices and store the result in biSizeImage.
pbmi->bmiHeader.biSizeImage = (pbmi->bmiHeader.biWidth + 7) / 8 * pbmi->bmiHeader.biHeight * cClrBits;

// Set biClrImportant to 0, indicating that all of the device colors are important.
pbmi->bmiHeader.biClrImportant = 0;


const PBITMAPINFOHEADER pbih = reinterpret_cast<PBITMAPINFOHEADER>(pbmi);              // bitmap info-header
const LPBYTE lpBits = static_cast<LPBYTE>(GlobalAlloc(GMEM_FIXED, pbih->biSizeImage)); // memory pointer

if (!lpBits) {
    DeleteDC(hdcScr);
    DeleteDC(hdcMem);
    LocalFree(pbmi);
    GlobalFree(lpBits);
    DeleteObject(hbmScr);
    return;
}

// Retrieve the color table (RGBQUAD array) and the bits (array of palette indices) from the DIB.
if (!GetDIBits(hdcMem, hbmScr, 0, pbih->biHeight, lpBits, pbmi, DIB_RGB_COLORS)) {
    DeleteDC(hdcScr);
    DeleteDC(hdcMem);
    LocalFree(pbmi);
    GlobalFree(lpBits);
    DeleteObject(hbmScr);
    return;
}

BITMAPFILEHEADER hdr; // bitmap file-header

hdr.bfType = 0x4d42; // ('M' << 8) + 'B';

// Calculate the size of the entire file.
hdr.bfSize = sizeof(BITMAPFILEHEADER) + pbih->biSize + pbih->biClrUsed * sizeof(RGBQUAD) + pbih->biSizeImage;
hdr.bfReserved1 = NULL;
hdr.bfReserved2 = NULL;

// Calculate the offset to the array of color indices.
hdr.bfOffBits = sizeof(BITMAPFILEHEADER) + pbih->biSize + pbih->biClrUsed * sizeof(RGBQUAD);


const DWORD cb = pbih->biSizeImage; // incremental count of bytes


std::stringstream outputBitmap;

// Write the BITMAPFILEHEADER into the .BMP file.
outputBitmap.write( reinterpret_cast<LPSTR>(&hdr), sizeof(BITMAPFILEHEADER));

// Write the BITMAPINFOHEADER and RGBQUAD array into the file.
outputBitmap.write(reinterpret_cast<LPSTR>(pbih), sizeof(BITMAPINFOHEADER) + pbih->biClrUsed * sizeof(RGBQUAD));

// Write the array of color indices
outputBitmap.write(reinterpret_cast<LPSTR>(lpBits), cb);




// To test the whole thing
std::ofstream out("test.bmp", std::ios::out | std::ios::binary);
out << outputBitmap.str();
out.close();


// Cleanup
DeleteDC(hdcScr);
DeleteDC(hdcMem);
LocalFree(pbmi);
GlobalFree(lpBits);
DeleteObject(hbmScr);

最佳答案

监视器可能具有负坐标，因此危险的是假设(0，0)是监视器的左上角†。实际原点(x，y)由系统指标SM_XVIRTUALSCREEN和SM_YVIRTUALSCREEN给出。然后，必须更新所有BLT以引用正确的源位置。这使得函数的第一位:

int x = GetSystemMetrics(SM_XVIRTUALSCREEN);
int y = GetSystemMetrics(SM_YVIRTUALSCREEN);
int w = GetSystemMetrics(SM_CXVIRTUALSCREEN);
int h = GetSystemMetrics(SM_CYVIRTUALSCREEN);

BOOL ok = StretchBlt(hdcMem, 0, 0, w, h, hdcScr, x, y, w, h, SRCCOPY);
// And So On...

另外，由于这类问题经常被问到，因此您可以使用类似于下面的非生产质量代码的代码来获得各个监视器:

#define WIN32_LEAN_AND_MEAN
#include <Windows.h>
#include <iostream>
using std::wcout;
using std::endl;

typedef struct tagMonData
{
    int current;
    MONITORINFOEXW* info;
} MonData;

BOOL EnumProc(HMONITOR hMonitor, HDC hdcMonitor, LPRECT lprcMonitor, LPARAM dwData)
{
    MonData* data = (MonData*)dwData;
    data->info[data->current].cbSize = sizeof(MONITORINFOEXW);
    return GetMonitorInfoW(hMonitor, &(data->info[data->current++]));
}

BOOL GetAllMonitorInfo(MonData* data)
{
    return EnumDisplayMonitors(NULL, NULL, (MONITORENUMPROC)(&EnumProc), (LPARAM)(data));
}

int main()
{
    int cMonitors = GetSystemMetrics(SM_CMONITORS);
    MonData data;
    data.current = 0;
    data.info = (MONITORINFOEXW*)calloc(cMonitors, sizeof(MONITORINFOEXW));

    if (!GetAllMonitorInfo(&data)) return 1;

    for (int i = 0; i < cMonitors; i++)
    {
        wcout << data.info[i].szDevice << "X: " << data.info[i].rcMonitor.left << " Y: " << data.info[i].rcMonitor.top << endl;
    }

    free(data.info);
    return 0;
}

请注意，如果GetMonitorInfoW调用由于某种原因失败，这将捷径并留下不完整的信息。

†Raymond Chen在The Old New Thing上写了几篇有关Windows坐标系统复杂性的文章