如何写出一个PNG屏幕截图？

Question

我在网上找到这个代码来打印屏幕（截图），但我不知道如何修改它以将结果保存到PNG文件。

我可以将位图保存到剪贴板，但我现在需要保存到PNG文件。

• 是否可以从剪贴板中提取位图并将其保存为PNG文件？
• 这可以做不同？
• 如果是这样，怎么样？

到目前为止我的代码是：

#include <iostream> 
#include <windows.h> 
#include <gdiplus.h> 
#include <stdexcept> 

using namespace std; 
using namespace Gdiplus; 
using namespace Gdiplus::DllExports; 
using std::runtime_error; 

void screenshot(POINT a, POINT b) 
{ 

    HDC  hScreen = GetDC(NULL); 
    HDC  hDc  = CreateCompatibleDC(hScreen); 
    HBITMAP hBitmap = CreateCompatibleBitmap(hScreen, abs(b.x-a.x), abs(b.y-a.y)); 
    HGDIOBJ old_obj = SelectObject(hDc, hBitmap); 
    BOOL bRet = BitBlt(hDc, 0, 0, abs(b.x-a.y), abs(b.y-a.y), hScreen, a.x, a.y, SRCCOPY); 

    OpenClipboard(NULL); 
    EmptyClipboard(); 
    SetClipboardData(CF_BITMAP, hBitmap); 
    CloseClipboard(); 


    SelectObject(hDc, old_obj); 
    DeleteDC(hDc); 
    ReleaseDC(NULL, hScreen); 
    DeleteObject(hBitmap); 
} 

int main() 
{ 
    POINT a,b; 
    a.x=386; 
    a.y=749; 

    b.x=686; 
    b.y=1049; 

    screenshot(a,b); 
} 

链接 - https://causeyourestuck.io/2016/01/12/screenshot-c-win32-api/ 作者奥马尔AFLAK

Answer 1

首先，包括Gdiplus库。在Visual Studio中，您可以使用#pragam关键字或在项目设置中添加Gdiplus.lib。

接下来，初始化Gdiplus与Gdiplus::GdiplusStartup

查找在前面提到的编码器CLSID。

在你的代码中你有abs(b.x-a.y)，据推测这应该是abs(b.x-a.x)。如果a应该是起点，则此逻辑可能不起作用。只要确保POINT b大于即可。或仔细阅读BitBlt

#include <Windows.h> 
#include "gdiplus.h" 

#pragma comment(lib, "Gdiplus.lib") 

int GetEncoderClsid(const WCHAR* format, CLSID* pClsid) 
{ 
    UINT num = 0;   // number of image encoders 
    UINT size = 0;   // size of the image encoder array in bytes 

    Gdiplus::GetImageEncodersSize(&num, &size); 
    if(size == 0) 
     return -1; // Failure 

    Gdiplus::ImageCodecInfo* pImageCodecInfo = (Gdiplus::ImageCodecInfo*)(malloc(size)); 
    if(pImageCodecInfo == NULL) 
     return -1; // Failure 

    GetImageEncoders(num, size, pImageCodecInfo); 

    for(UINT j = 0; j < num; ++j) 
    { 
     if(wcscmp(pImageCodecInfo[j].MimeType, format) == 0) 
     { 
      *pClsid = pImageCodecInfo[j].Clsid; 
      free(pImageCodecInfo); 
      return j; // Success 
     } 
    } 

    free(pImageCodecInfo); 
    return -1; // Failure 
} 

void screenshot(POINT a, POINT b) 
{ 
    int w = b.x - a.x; 
    int h = b.y - a.y; 

    if(w <= 0) return; 
    if(h <= 0) return; 

    HDC  hScreen = GetDC(HWND_DESKTOP); 
    HDC  hDc = CreateCompatibleDC(hScreen); 
    HBITMAP hBitmap = CreateCompatibleBitmap(hScreen, w, h); 
    HGDIOBJ old_obj = SelectObject(hDc, hBitmap); 
    BitBlt(hDc, 0, 0, w, h, hScreen, a.x, a.y, SRCCOPY); 

    Gdiplus::Bitmap bitmap(hBitmap, NULL); 
    CLSID clsid; 
    GetEncoderClsid(L"image/png", &clsid); 
    bitmap.Save(L"c:\\test\\test.png", &clsid); 

    SelectObject(hDc, old_obj); 
    DeleteDC(hDc); 
    ReleaseDC(HWND_DESKTOP, hScreen); 
    DeleteObject(hBitmap); 
} 

int WINAPI wWinMain(HINSTANCE, HINSTANCE, LPTSTR, int) 
{ 
    Gdiplus::GdiplusStartupInput gdiplusStartupInput; 
    ULONG_PTR gdiplusToken; 
    Gdiplus::GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL); 

    RECT  rc; 
    GetClientRect(GetDesktopWindow(), &rc); 
    POINT a{ 0, 0 }; 
    POINT b{ 100, 100 }; 

    screenshot(a, b); 

    Gdiplus::GdiplusShutdown(gdiplusToken); 

    return 0; 
}