Take a screenshot and write it out as a JPEG in C++ on Windows

screen_grab.cpp

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

using namespace Gdiplus;
using namespace std;

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

    ImageCodecInfo* pImageCodecInfo = NULL;

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

    pImageCodecInfo = (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 BitmapToJpg(HBITMAP hbmpImage, int width, int height)
{
    Bitmap *p_bmp = Bitmap::FromHBITMAP(hbmpImage, NULL);
    //Bitmap *p_bmp = new Bitmap(width, height, PixelFormat32bppARGB);
    
    CLSID pngClsid;
    int result = GetEncoderClsid(L"image/jpeg", &pngClsid);
    if(result != -1)
        std::cout << "Encoder succeeded" << std::endl;
    else
        std::cout << "Encoder failed" << std::endl;
    p_bmp->Save(L"screen.jpg", &pngClsid, NULL);
    delete p_bmp;
}

bool ScreenCapture(int x, int y, int width, int height, char *filename)
{
    HDC hDc = CreateCompatibleDC(0);
    HBITMAP hBmp = CreateCompatibleBitmap(GetDC(0), width, height);
    SelectObject(hDc, hBmp);
    BitBlt(hDc, 0, 0, width, height, GetDC(0), x, y, SRCCOPY);
    BitmapToJpg(hBmp, width, height);
    DeleteObject(hBmp);
    return true;
}

int main() {
    // Initialize GDI+.
    GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
    
    int x1 = 0;
    int y1 = 0;
    int x2 = GetSystemMetrics(SM_CXSCREEN);
    int y2 = GetSystemMetrics(SM_CYSCREEN);
    ScreenCapture(x1, y1, x2 - x1, y2 - y1, "screen.jpg");
    
    //Shutdown GDI+
    GdiplusShutdown(gdiplusToken);
    
    return 0;
}

awesome, great job!

Simple as it can be. If you get unresolved externals, do not forget to link with Gdiplus.lib

Looks like filename isn't used anywhere in your ScreenCapture function

Hi, I'm a C++ greenhorn.
Can anyone write how to "link with Gdiplus.lib"?

add this after #include
#pragma comment (lib,"Gdiplus.lib")

WTF?!

what for a argument "filename" in function "bool ScreenCapture()"?
he does nothing

Very great job, but the image seems to lose lot of quality

Great stuff! Thanks for this!

In mingw if error: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
Change: bool ScreenCapture(int x, int y, int width, int height, char *filename)
To: bool ScreenCapture(int x, int y, int width, int height, char *filename = (char *)"");

Just copied your code and compiled !
+1 star for simplicity

niubility