屏幕捕获无法使用C ++和GDI捕获整个屏幕 [英] Screen capture fails to capture whole screen using C++ and GDI
问题描述
我通过网络进行了一些研究，发现了一些有用的代码.我进行了一些更改，以尝试捕获整个屏幕并生成一个可以通过udp数据包发送的缓冲区:
#include <iostream>
#include <Windows.h>
#include <fstream>
void CapruteScreenAndSaveToFile()
{
uint16_t BitsPerPixel = 24;
uint32_t Width = GetSystemMetrics(SM_CXSCREEN);
uint32_t Height = GetSystemMetrics(SM_CYSCREEN);
// Create Header
BITMAPFILEHEADER Header;
memset(&Header, 0, sizeof(Header));
Header.bfType = 0x4D42;
Header.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
// Create Info
BITMAPINFO Info;
memset(&Info, 0, sizeof(Info));
Info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
Info.bmiHeader.biWidth = Width;
Info.bmiHeader.biHeight = Height;
Info.bmiHeader.biPlanes = 1;
Info.bmiHeader.biBitCount = BitsPerPixel;
Info.bmiHeader.biCompression = BI_RGB;
Info.bmiHeader.biSizeImage = Width * Height * (BitsPerPixel > 24 ? 4 : 3);
// Capture screen and save to Pixels
char* Pixels = NULL;
HDC MemDC = CreateCompatibleDC(0);//Context);
HBITMAP Section = CreateDIBSection(MemDC, &Info, DIB_RGB_COLORS, (void**)&Pixels, 0, 0);
DeleteObject(SelectObject(MemDC, Section));
BitBlt(MemDC, 0, 0, Width, Height, GetDC(0), 0, 0, SRCCOPY);
DeleteDC(MemDC);
// Concatenate everything
char * buffer = (char*)malloc(sizeof(Header) + sizeof(Info.bmiHeader) + (((BitsPerPixel * Width + 31) & ~31) / 8) * Height);
memcpy(buffer, (char*)&Header, sizeof(Header));
memcpy(buffer + sizeof(Header), (char*)&Info.bmiHeader, sizeof(Info.bmiHeader));
memcpy(buffer + sizeof(Header) + sizeof(Info.bmiHeader), Pixels, (((BitsPerPixel * Width + 31) & ~31) / 8) * Height);
// Save to file
std::fstream hFile("Foo.bmp", std::ios::out | std::ios::binary);
hFile.write(buffer, sizeof(Header) + sizeof(Info.bmiHeader) + (((BitsPerPixel * Width + 31) & ~31) / 8) * Height);
// Clean up
hFile.close();
DeleteObject(Section);
free(buffer);
}
int main()
{
CapruteScreenAndSaveToFile();
return 0;
}
但它似乎只能捕获我桌面的这一部分:
即使我使用CreateCompatibleDC(0)，也是如此.
如果计算机的DPI设置较高，并且应用程序不支持DPI，则系统将欺骗该应用程序，并给出错误的屏幕尺寸. /p>
您会发现以下代码显示的宽度和高度小于实际屏幕尺寸:
uint32_t Width = GetSystemMetrics(SM_CXSCREEN);
uint32_t Height = GetSystemMetrics(SM_CYSCREEN);
std::cout << Width << " x " << Height << "\n";
解决方案是添加 DPI意识申请.
要添加DPI兼容性:
在Visual Studio 2015中，转到项目属性"->清单工具"，将DPI感知设置为每台监视器具有较高的DPI感知"或具有较高的DPI感知"
如果您使用的是旧的编译器...
1)创建具有以下内容的文件"myapp.manifest":
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<application xmlns="urn:schemas-microsoft-com:asm.v3">
<windowsSettings>
<dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">True/PM</dpiAware>
</windowsSettings>
</application>
</assembly>
2)将* .rc文件添加到您的项目中，内容如下:
1 24 "myapp.manifest"
3)重建项目
I made some research through the web, and found some useful code. I changed it a bit, in attempt to capture the whole screen and generate a buffer that I can send through udp packets:
#include <iostream>
#include <Windows.h>
#include <fstream>
void CapruteScreenAndSaveToFile()
{
uint16_t BitsPerPixel = 24;
uint32_t Width = GetSystemMetrics(SM_CXSCREEN);
uint32_t Height = GetSystemMetrics(SM_CYSCREEN);
// Create Header
BITMAPFILEHEADER Header;
memset(&Header, 0, sizeof(Header));
Header.bfType = 0x4D42;
Header.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
// Create Info
BITMAPINFO Info;
memset(&Info, 0, sizeof(Info));
Info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
Info.bmiHeader.biWidth = Width;
Info.bmiHeader.biHeight = Height;
Info.bmiHeader.biPlanes = 1;
Info.bmiHeader.biBitCount = BitsPerPixel;
Info.bmiHeader.biCompression = BI_RGB;
Info.bmiHeader.biSizeImage = Width * Height * (BitsPerPixel > 24 ? 4 : 3);
// Capture screen and save to Pixels
char* Pixels = NULL;
HDC MemDC = CreateCompatibleDC(0);//Context);
HBITMAP Section = CreateDIBSection(MemDC, &Info, DIB_RGB_COLORS, (void**)&Pixels, 0, 0);
DeleteObject(SelectObject(MemDC, Section));
BitBlt(MemDC, 0, 0, Width, Height, GetDC(0), 0, 0, SRCCOPY);
DeleteDC(MemDC);
// Concatenate everything
char * buffer = (char*)malloc(sizeof(Header) + sizeof(Info.bmiHeader) + (((BitsPerPixel * Width + 31) & ~31) / 8) * Height);
memcpy(buffer, (char*)&Header, sizeof(Header));
memcpy(buffer + sizeof(Header), (char*)&Info.bmiHeader, sizeof(Info.bmiHeader));
memcpy(buffer + sizeof(Header) + sizeof(Info.bmiHeader), Pixels, (((BitsPerPixel * Width + 31) & ~31) / 8) * Height);
// Save to file
std::fstream hFile("Foo.bmp", std::ios::out | std::ios::binary);
hFile.write(buffer, sizeof(Header) + sizeof(Info.bmiHeader) + (((BitsPerPixel * Width + 31) & ~31) / 8) * Height);
// Clean up
hFile.close();
DeleteObject(Section);
free(buffer);
}
int main()
{
CapruteScreenAndSaveToFile();
return 0;
}
But it only seems to capture this part of my desktop:
And that's even though I use CreateCompatibleDC(0).
If the computer is on high DPI settings, and the application is not DPI aware, then the system will lie to the application and give the wrong screen size.
You will find the following code shows width and height which are smaller than the actual screen size:
uint32_t Width = GetSystemMetrics(SM_CXSCREEN);
uint32_t Height = GetSystemMetrics(SM_CYSCREEN);
std::cout << Width << " x " << Height << "\n";
The solution is to add DPI awareness to application.
To add DPI compatibility:
In Visual Studio 2015, go to Project Properties -> Manifest tools, set DPI awareness to "Per Monitor High DPI Aware" or "High DPI Aware"
If you are using some old compiler...
1) create a file "myapp.manifest" with this content:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<application xmlns="urn:schemas-microsoft-com:asm.v3">
<windowsSettings>
<dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">True/PM</dpiAware>
</windowsSettings>
</application>
</assembly>
2) Add *.rc file to your project with this content:
1 24 "myapp.manifest"
3) Rebuild the project
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