截图在C++

Question

This is the screenshot my program takes:

I try to make a C++ program that takes a screenshot and saves it as png. Everthing works except it takes a screenshot of just the top left of the screen.

The problem is that my application takes a picture of the top left corner of my desktop.

How can I take a screenshot of the WHOLE screen? What do I have to change in my code to reach my goal?

This is my code:

#define _CRT_SECURE_NO_WARNINGS

#include <windows.h>
#include <objidl.h>
#include <stdio.h>
#include <gdiplus.h>
using namespace Gdiplus;
#pragma comment (lib,"Gdiplus.lib")

int GetEncoderClsid(const WCHAR* format, CLSID* pClsid) {
    UINT num = 0;
    UINT size = 0;
    Gdiplus::ImageCodecInfo* pImageCodecInfo = NULL;

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

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

    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;
        }
    }

    free(pImageCodecInfo);
    return -1;
}

void TakeScreenshot(const wchar_t* file_name) {
    // Get the dimensions of the whole desktop
    int width = GetSystemMetrics(SM_CXVIRTUALSCREEN);
    int height = GetSystemMetrics(SM_CYVIRTUALSCREEN);

    // Create a bitmap to hold the screenshot
    HDC screen_dc = GetDC(NULL);
    HDC mem_dc = CreateCompatibleDC(screen_dc);
    HBITMAP bitmap = CreateCompatibleBitmap(screen_dc, width, height);
    HGDIOBJ old_bitmap = SelectObject(mem_dc, bitmap);

    // Copy the screen contents to the bitmap
    BitBlt(mem_dc, 0, 0, width, height, screen_dc, 0, 0, SRCCOPY);

    // Save the bitmap to a file
    Gdiplus::Bitmap image(bitmap, NULL);
    CLSID png_clsid;
    GetEncoderClsid(L"image/png", &png_clsid);
    image.Save((WCHAR*)file_name, &png_clsid, NULL);

    // Clean up
    SelectObject(mem_dc, old_bitmap);
    DeleteObject(bitmap);
    DeleteDC(mem_dc);
    ReleaseDC(NULL, screen_dc);
}

int main()
{
    Gdiplus::GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    TakeScreenshot(L"test.png");

    GdiplusShutdown(gdiplusToken);
}

Updated code:

#define _CRT_SECURE_NO_WARNINGS

#include <windows.h>
#include <objidl.h>
#include <stdio.h>
#include <gdiplus.h>
using namespace Gdiplus;
#pragma comment (lib,"Gdiplus.lib")

int GetEncoderClsid(const WCHAR* format, CLSID* pClsid)
{
    UINT num = 0;
    UINT size = 0;
    Gdiplus::ImageCodecInfo* pImageCodecInfo = NULL;

    Gdiplus::GetImageEncodersSize(&num, &size);
    if (size == 0) {
        printf("Error: GetImageEncodersSize returned size 0\n");
        return -1;
    }

    pImageCodecInfo = (Gdiplus::ImageCodecInfo*)(malloc(size));
    if (pImageCodecInfo == NULL) {
        printf("Error: malloc failed to allocate memory for ImageCodecInfo\n");
        return -1;
    }

    if (GetImageEncoders(num, size, pImageCodecInfo) != Ok) {
        printf("Error: GetImageEncoders failed\n");
        free(pImageCodecInfo);
        return -1;
    }

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

    free(pImageCodecInfo);
    return -1;
}

void TakeScreenshot(const wchar_t* file_name)
{
    // Get the dimensions of the whole desktop
    int dpi_x = GetDpiForSystem();
    int dpi_y = GetDpiForSystem();
    int width = GetSystemMetricsForDpi(SM_CXSCREEN, dpi_x);
    int height = GetSystemMetricsForDpi(SM_CYSCREEN, dpi_y);

    if (width == 0 || height == 0) {
        printf("Error: GetSystemMetrics returned invalid screen dimensions\n");
        return;
    }

    printf("Width: %d\n", width);
    printf("Height: %d\n", height);

    // Create a bitmap to hold the screenshot
    HDC screen_dc = GetDC(NULL);
    if (screen_dc == NULL) {
        printf("Error: GetDC failed to get a handle to the screen device context\n");
        return;
    }

    HDC mem_dc = CreateCompatibleDC(screen_dc);
    if (mem_dc == NULL) {
        printf("Error: CreateCompatibleDC failed to create a compatible device context\n");
        ReleaseDC(NULL, screen_dc);
        return;
    }

    // Create a bitmap that is scaled to the appropriate DPI
    HBITMAP bitmap = CreateBitmap(width, height, 1, GetDeviceCaps(screen_dc, BITSPIXEL), NULL);
    if (bitmap == NULL) {
        printf("Error: CreateCompatibleBitmap failed to create a compatible bitmap\n");
        DeleteDC(mem_dc);
        ReleaseDC(NULL, screen_dc);
        return;
    }

    HGDIOBJ old_bitmap = SelectObject(mem_dc, bitmap);

    // Set the DPI of the memory DC to match the system DPI
    SetGraphicsMode(mem_dc, GM_ADVANCED);
    XFORM xform;
    xform.eM11 = (FLOAT)dpi_x / 96;
    xform.eM12 = xform.eM21 = xform.eM22 = 0;
    xform.eDx = xform.eDy = 0;
    SetWorldTransform(mem_dc, &xform);

    // Copy the screen contents to the bitmap
    if (BitBlt(mem_dc, 0, 0, width, height, screen_dc, 0, 0, SRCCOPY) == 0) {
        printf("Error:BitBlt failed to copy screen contents to bitmap\n");
        return;
    }

    // Save the bitmap to a file
    Gdiplus::Bitmap image(bitmap, NULL);
    if (image.GetLastStatus() != Ok) {
        printf("Error: Bitmap constructor failed to create a Bitmap object\n");
        return;
    }

    CLSID png_clsid;
    int r = GetEncoderClsid(L"image/png", &png_clsid);
    if (r == -1)
    {
        printf("Error: unable to find image encoder for MIME type 'image/png'\n");
        return;
    }

    if (image.Save(file_name, &png_clsid, NULL) != Ok) {
        printf("Error: Bitmap::Save failed to save image\n");
        return;
    }

    // Clean up
    SelectObject(mem_dc, old_bitmap);
    DeleteObject(bitmap);
    DeleteDC(mem_dc);
    ReleaseDC(NULL, screen_dc);
}

int main()
{
    GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    TakeScreenshot(L"test.png");

    GdiplusShutdown(gdiplusToken);
    return 0;
}

Answer 1

As @AndreasWenzel said, I have to make the application DPI-aware. This code works perfectly:

#define _CRT_SECURE_NO_WARNINGS

#include <windows.h>
#include <objidl.h>
#include <stdio.h>
#include <gdiplus.h>
using namespace Gdiplus;
#pragma comment (lib,"Gdiplus.lib")

int GetEncoderClsid(const WCHAR* format, CLSID* pClsid)
{
    UINT num = 0;
    UINT size = 0;
    Gdiplus::ImageCodecInfo* pImageCodecInfo = NULL;

    Gdiplus::GetImageEncodersSize(&num, &size);
    if (size == 0) {
        printf("Error: GetImageEncodersSize returned size 0\n");
        return -1;
    }

    pImageCodecInfo = (Gdiplus::ImageCodecInfo*)(malloc(size));
    if (pImageCodecInfo == NULL) {
        printf("Error: malloc failed to allocate memory for ImageCodecInfo\n");
        return -1;
    }

    if (GetImageEncoders(num, size, pImageCodecInfo) != Ok) {
        printf("Error: GetImageEncoders failed\n");
        free(pImageCodecInfo);
        return -1;
    }

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

    free(pImageCodecInfo);
    return -1;
}

void TakeScreenshot(const wchar_t* file_name)
{
    // Get the dimensions of the whole desktop
    int dpi_x = GetDpiForSystem();
    int dpi_y = GetDpiForSystem();
    int width = GetSystemMetricsForDpi(SM_CXSCREEN, dpi_x);
    int height = GetSystemMetricsForDpi(SM_CYSCREEN, dpi_y);

    if (width == 0 || height == 0) {
        printf("Error: GetSystemMetrics returned invalid screen dimensions\n");
        return;
    }

    printf("Width: %d\n", width);
    printf("Height: %d\n", height);

    // Create a bitmap to hold the screenshot
    HDC screen_dc = GetDC(NULL);
    if (screen_dc == NULL) {
        printf("Error: GetDC failed to get a handle to the screen device context\n");
        return;
    }

    HDC mem_dc = CreateCompatibleDC(screen_dc);
    if (mem_dc == NULL) {
        printf("Error: CreateCompatibleDC failed to create a compatible device context\n");
        ReleaseDC(NULL, screen_dc);
        return;
    }

    // Create a bitmap that is scaled to the appropriate DPI
    HBITMAP bitmap = CreateBitmap(width, height, 1, GetDeviceCaps(screen_dc, BITSPIXEL), NULL);
    if (bitmap == NULL) {
        printf("Error: CreateCompatibleBitmap failed to create a compatible bitmap\n");
        DeleteDC(mem_dc);
        ReleaseDC(NULL, screen_dc);
        return;
    }

    HGDIOBJ old_bitmap = SelectObject(mem_dc, bitmap);

    // Set the DPI of the memory DC to match the system DPI
    SetGraphicsMode(mem_dc, GM_ADVANCED);
    XFORM xform;
    xform.eM11 = (FLOAT)dpi_x / 96;
    xform.eM12 = xform.eM21 = xform.eM22 = 0;
    xform.eDx = xform.eDy = 0;
    SetWorldTransform(mem_dc, &xform);

    // Copy the screen contents to the bitmap
    if (BitBlt(mem_dc, 0, 0, width, height, screen_dc, 0, 0, SRCCOPY) == 0) {
        printf("Error:BitBlt failed to copy screen contents to bitmap\n");
        return;
    }

    // Save the bitmap to a file
    Gdiplus::Bitmap image(bitmap, NULL);
    if (image.GetLastStatus() != Ok) {
        printf("Error: Bitmap constructor failed to create a Bitmap object\n");
        return;
    }

    CLSID png_clsid;
    int r = GetEncoderClsid(L"image/png", &png_clsid);
    if (r == -1)
    {
        printf("Error: unable to find image encoder for MIME type 'image/png'\n");
        return;
    }

    if (image.Save(file_name, &png_clsid, NULL) != Ok) {
        printf("Error: Bitmap::Save failed to save image\n");
        return;
    }

    // Clean up
    SelectObject(mem_dc, old_bitmap);
    DeleteObject(bitmap);
    DeleteDC(mem_dc);
    ReleaseDC(NULL, screen_dc);
}

int main()
{
    GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    DPI_AWARENESS_CONTEXT dpi_awareness_context = SetThreadDpiAwarenessContext(DPI_AWARENESS_CONTEXT_SYSTEM_AWARE);

    TakeScreenshot(L"test.png");

    SetThreadDpiAwarenessContext(dpi_awareness_context);

    GdiplusShutdown(gdiplusToken);
    return 0;
}