How to save a GDI+ HDC to bitmap file? - c++

Question

I'm trying to save the content of a hdc to a bitmap file, I'm currently using the code above, it does save an image, but I can't open it.
Looks like it's corrupted, and it always has the same size (54bytes).
I might be doing something wrong in the HDCTofile function.
#include <vector> // HDCToFile
#include <fstream>
#include <cstring>
#include <windows.h>
HDCToFile("output.bmp", hdc);
bool HDCToFile(const char* FilePath, HDC Context, uint16_t BitsPerPixel = 24)
{
//uint32_t Width = Area.right - Area.left;
//uint32_t Height = Area.bottom - Area.top;
BITMAPINFO Info;
BITMAPFILEHEADER Header;
memset(&Info, 0, sizeof(Info));
memset(&Header, 0, sizeof(Header));
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);
Header.bfType = 0x4D42;
Header.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
char* Pixels = NULL;
HDC MemDC = CreateCompatibleDC(Context);
HBITMAP Section = CreateDIBSection(Context, &Info, DIB_RGB_COLORS, (void**)&Pixels, 0, 0);
DeleteObject(SelectObject(MemDC, Section));
BitBlt(MemDC, 0, 0, Info.bmiHeader.biWidth, Info.bmiHeader.biHeight, Context, 0, 0, SRCCOPY);
DeleteDC(MemDC);
std::fstream hFile(FilePath, std::ios::out | std::ios::binary);
if (hFile.is_open())
{
hFile.write((char*)&Header, sizeof(Header));
hFile.write((char*)&Info.bmiHeader, sizeof(Info.bmiHeader));
hFile.write(Pixels, (((BitsPerPixel * Info.bmiHeader.biWidth + 31) & ~31) / 8) * Info.bmiHeader.biHeight);
hFile.close();
DeleteObject(Section);
return true;
}
DeleteObject(Section);
return false;
}

Answer 1

Your works are almost done, just add the DC size information into the bitmapfileheader and bitmap info :
BITMAP structBitmapHeader;
memset(&structBitmapHeader, 0, sizeof(BITMAP));
HGDIOBJ hBitmap = GetCurrentObject(Context, OBJ_BITMAP);
GetObject(hBitmap, sizeof(BITMAP), &structBitmapHeader);
uint32_t Width = structBitmapHeader.bmWidth;
uint32_t Height = structBitmapHeader.bmHeight;
BITMAPINFO Info;
BITMAPFILEHEADER Header;
memset(&Info, 0, sizeof(Info));
memset(&Header, 0, sizeof(Header));
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);
Header.bfType = 0x4D42;
Header.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
//--- your code to draw DC into bitmap ----