解决使用复制浏览器的屏幕截图出现黑色窗口的问题

Posted 2021-03-22 strive-sun

前提：使用电子应用程序，QT，WPF ...等框架制作的应用程序将响应GetDC或打印黑屏GetWindowDC。解决此问题的唯一方法是确保目标应用程序可见，并在目标应用程序所在的特定坐标处为桌面截图

C++代码：

#include <fstream>
#include <vector>
#include <windows.h>

int main() 
{
    //make sure process is DPI aware
    SetProcessDPIAware();

    HWND hwnd_target = FindWindowA("Notepad", NULL);
    if(!hwnd_target)
        return 0;

    //make sure target window is on top
    SetForegroundWindow(hwnd_target);
    Sleep(250);

    //get hdc of desktop
    HDC hdc = GetDC(HWND_DESKTOP);

    //copy bits from coordinates of target window
    RECT rc;
    GetWindowRect(hwnd_target, &rc);
    int w = rc.right - rc.left;
    int h = rc.bottom - rc.top;
    HDC memdc = CreateCompatibleDC(hdc);
    HBITMAP hbitmap = CreateCompatibleBitmap(hdc, w, h);
    HGDIOBJ oldbmp = SelectObject(memdc, hbitmap);
    BitBlt(memdc, 0, 0, w, h, hdc, rc.left, rc.top, SRCCOPY | CAPTUREBLT);
    SelectObject(memdc, oldbmp);
    DeleteDC(memdc);

    //restore the foreground
    SetForegroundWindow(GetConsoleWindow());

    //save to file
    BITMAPINFOHEADER bi = { sizeof(bi), w, h, 1, 32 };
    std::vector<BYTE> pixels(w * h * 4);
    GetDIBits(hdc, hbitmap, 0, h, pixels.data(), 
        (BITMAPINFO*)&bi, DIB_RGB_COLORS);

    std::ofstream fout("filename.bmp", std::ios::binary);
    BITMAPFILEHEADER hdr = { ‘MB‘, 54 + bi.biSizeImage, 0, 0, 54 };
    fout.write((char*)&hdr, 14);
    fout.write((char*)&bi, 40);
    fout.write((char*)pixels.data(), pixels.size());

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

    return 0;
}

python代码：

import win32gui
import win32ui
import win32con
from ctypes import windll
from PIL import Image
import time
import ctypes

hwnd_target = win32gui.FindWindow(None, ‘Calculator‘) #Chrome handle be used for test 

left, top, right, bot = win32gui.GetWindowRect(hwnd_target)
w = right - left
h = bot - top

win32gui.SetForegroundWindow(hwnd_target)
time.sleep(1.0)

hdesktop = win32gui.GetDesktopWindow()
hwndDC = win32gui.GetWindowDC(hdesktop)
mfcDC  = win32ui.CreateDCFromHandle(hwndDC)
saveDC = mfcDC.CreateCompatibleDC()

saveBitMap = win32ui.CreateBitmap()
saveBitMap.CreateCompatibleBitmap(mfcDC, w, h)

saveDC.SelectObject(saveBitMap)

result = saveDC.BitBlt((0, 0), (w, h), mfcDC, (left, top), win32con.SRCCOPY)

bmpinfo = saveBitMap.GetInfo()
bmpstr = saveBitMap.GetBitmapBits(True)

im = Image.frombuffer(
    ‘RGB‘,
    (bmpinfo[‘bmWidth‘], bmpinfo[‘bmHeight‘]),
    bmpstr, ‘raw‘, ‘BGRX‘, 0, 1)

win32gui.DeleteObject(saveBitMap.GetHandle())
saveDC.DeleteDC()
mfcDC.DeleteDC()
win32gui.ReleaseDC(hdesktop, hwndDC)

if result == None:
    #PrintWindow Succeeded
    im.save("test.png")

注意：拷贝firefox浏览器的屏幕截图有点麻烦，因为firefox的窗口句柄是无窗口句柄，只能使用UI自动化来获取，具体操作我暂时也不会。