使用位图仅捕获部分屏幕 (C)

Question

我在使用 BitBlt() try catch 位于屏幕正中心的全宽、1 像素高的图像时遇到问题。

HDC hdcTemp;
BYTE* bitPointer;
int x, y;
int red, green, blue, alpha;

HDC desktopWindow = GetDC(HWND_DESKTOP);
//GetWindowRect(hWND_Desktop, &rect);
int screenWidth = GetSystemMetrics(SM_CXSCREEN);
int screenHeight = GetSystemMetrics(SM_CYSCREEN);
int wPos = screenWidth / 2;
int hPos = screenHeight / 2;
int screenShotWidth = screenWidth;
int screenShotHeight = 1;

while (true)
{

    hdcTemp = CreateCompatibleDC(desktopWindow);
    BITMAPINFO bitmap;
    bitmap.bmiHeader.biSize = sizeof(bitmap.bmiHeader);
    bitmap.bmiHeader.biWidth = screenShotWidth;
    bitmap.bmiHeader.biHeight = screenShotHeight;
    bitmap.bmiHeader.biPlanes = 1;
    bitmap.bmiHeader.biBitCount = 24;
    bitmap.bmiHeader.biCompression = BI_RGB;
    bitmap.bmiHeader.biSizeImage = screenShotWidth * 4 * screenShotHeight;
    bitmap.bmiHeader.biClrUsed = 0;
    bitmap.bmiHeader.biClrImportant = 0;
    HBITMAP hBitmap2 = CreateDIBSection(hdcTemp, &bitmap, DIB_RGB_COLORS, (void**)(&bitPointer), NULL, NULL);
    SelectObject(hdcTemp, hBitmap2);
    BitBlt(hdcTemp, 0, 0, screenShotWidth, screenShotHeight, desktopWindow, 0, hPos-1 ,SRCCOPY);

    for (int i = 0; i < (screenShotWidth * 4 * screenShotHeight); i += 4)
    {
        red = (int)bitPointer[i];
        green = (int)bitPointer[i + 1];
        blue = (int)bitPointer[i + 2];

        x = i / (4 * screenShotHeight);
        y = i / (4 * screenShotWidth);
        std::cout << "r : " << red << " x: " << x <<  " y: " << y <<  "\n";
    }
    std::this_thread::sleep_for(std::chrono::milliseconds(2));
}

我知道在全屏捕获时 BitBlt() 需要如下所示:

BitBlt(hdcTemp, 0, 0, screenWidth, screenHeight, desktopWindow, 0, 0 ,SRCCOPY);

我只是不知道要更改什么才能使其仅捕获我想要捕获的位于屏幕中间的部分......

Answer 1

bitmap.bmiHeader.biSizeImage = screenShotWidth * 4 * screenShotHeight;

对于 24 位位图大小，应按如下方式计算:

int size = ((screenShotWidth * 24 + 31) / 32) * 4 * screenShotHeight;

请注意，24 位位图没有 Alpha channel ，每个像素 3 个字节。将增量更改为以下内容:

for(int i = 0; i < (screenShotWidth * 3 * screenShotHeight); i += 3)
{
    red = (int)bitPointer[i];
    green = (int)bitPointer[i + 1];
    blue = (int)bitPointer[i + 2];
    ...
}

为了让事情变得更容易，您还可以使用 32 位位图。