Taking a screenshot in DirectDraw

How do I take a screenshot in fullscreen directdraw.

I hit alt+printscrn, and also only printscrn, but I only get the white window created in the beginning of the program.

Do I need some technique or (ugh) software?

Code one.

Simply iterate through your primary surface and write the values to disk - which will be huge in 32-bit color. Another alternative is to use RLE or make a function that will create a BMP out of the data. Then most programs could load your screenshot.

whats RLE?

This code below uses DirectDraw (DX7) but it's easily enough altered to work with other API's. For instance, for my OpenGL wrapper I pass HDCs directly instead of passing a DX surface and having to grab the HDC from it.

Inside of "Types.h" I have:
typedef LPDIRECTDRAWSURFACE7 lpdds7;

Code:

#pragma once

#include "Types.h"
#include <string>
using std::string;

void SaveScreen(lpdds7 sfHDC);
PBITMAPINFO MakeBI(lpdds7 sfHDC);

Code:

#include "ScreenCapture.h"

HBITMAP NewBmp=NULL, OldBmp=NULL;
HDC hdcCom=NULL;

void SaveScreen(lpdds7 sfHDC)
{
	HANDLE hf;
	BITMAPFILEHEADER hdr;
	PBITMAPINFOHEADER pbih;
	LPBYTE lpBits;
	DWORD dwTotal;
	DWORD cb;
	BYTE *hp;
	DWORD dwTmp;
	PBITMAPINFO pbiTest=MakeBI(sfHDC);
	pbih=(PBITMAPINFOHEADER) pbiTest;
	lpBits=(LPBYTE)GlobalAlloc(GMEM_FIXED,pbih->biSizeImage);
	GetDIBits(hdcCom,NewBmp,0,(WORD)pbih->biHeight,lpBits,pbiTest,DIB_RGB_COLORS);
	//lpwin32_find_data
	WIN32_FIND_DATA finddata;
	string sBitmapName;
	int iFileCheck=1;
	hf=FindFirstFile("screen*.bmp",&finddata);
	if(hf==INVALID_HANDLE_VALUE)
	{
		sBitmapName="screen0.bmp";
	}
	else
	{
		while(iFileCheck)
		{
			iFileCheck=FindNextFile(hf,&finddata);
		}
		string sLastBitmapFound=finddata.cFileName;
		string sFileID="";
		char cID[5];
		int EndOfID, ID, i;
		for(i=6;i<sLastBitmapFound.size();i++)
		{
			if(!isdigit(sLastBitmapFound[i]))
			{
				EndOfID=i;
				break;
			}
		}
		for(i=6;i<EndOfID;i++)
		{
			sFileID+=sLastBitmapFound[i];
		}
		ID=atoi(sFileID.c_str());
		ID++;
		itoa(ID,cID,10);
		sBitmapName="screen";
		sBitmapName+=cID;
		sBitmapName+=".bmp";
		DebugLog(sBitmapName.c_str(),ID,1);
	}
	hf=CreateFile(sBitmapName.c_str(),GENERIC_WRITE,0,NULL,CREATE_ALWAYS,FILE_ATTRIBUTE_NORMAL,NULL);
	hdr.bfType=0x4d42;
	hdr.bfSize=(DWORD)(sizeof(BITMAPFILEHEADER)+pbih->biSize+pbih->biClrUsed*sizeof(RGBQUAD)+pbih->biSizeImage);
	hdr.bfReserved1=0;
	hdr.bfReserved2=0;
	hdr.bfOffBits=(DWORD)sizeof(BITMAPFILEHEADER)+pbih->biSize+pbih->biClrUsed*sizeof(RGBQUAD);
	WriteFile(hf,(LPVOID)&hdr,sizeof(BITMAPFILEHEADER),(LPDWORD)&dwTmp,NULL);
	WriteFile(hf,(LPVOID)pbih,sizeof(BITMAPINFOHEADER)+pbih->biClrUsed*sizeof(RGBQUAD),(LPDWORD)&dwTmp,NULL);
	dwTotal=cb=pbih->biSizeImage;
	hp=lpBits;
	WriteFile(hf,(LPSTR)hp,(int)cb,(LPDWORD)&dwTmp,NULL);
	CloseHandle(hf);
	DebugLog("Scree capture recorded.",0,1);
	GlobalFree((HGLOBAL)lpBits);
	SelectObject(hdcCom,OldBmp);
	DeleteObject(NewBmp);
	NewBmp=NULL;
	DeleteDC(hdcCom);
	hdcCom=NULL;
}

PBITMAPINFO MakeBI(lpdds7 sfHDC)
{
	BITMAP bmp;
	PBITMAPINFO pbmi;
	WORD cClrBits;
	HDC hdc;
	sfHDC->GetDC(&hdc);
	NewBmp=CreateCompatibleBitmap(hdc,800,600);
	hdcCom=CreateCompatibleDC(hdc);
	OldBmp=(HBITMAP)SelectObject(hdcCom,NewBmp);
	BitBlt(hdcCom,0,0,800,600,hdc,0,0,SRCCOPY);
	sfHDC->ReleaseDC(hdc);
	hdc=NULL;
	GetObject(NewBmp,sizeof(BITMAP),(LPSTR)&bmp);
	cClrBits=(WORD)(bmp.bmPlanes*bmp.bmBitsPixel);
	if(cClrBits==1)
		cClrBits=1;
	else if(cClrBits<=4)
		cClrBits=4;
	else if(cClrBits<=8)
		cClrBits=8;
	else if(cClrBits<=16)
		cClrBits=16;
	else if(cClrBits<=24)
		cClrBits=24;
	else cClrBits=32;
	if(cClrBits!=24)
		pbmi=(PBITMAPINFO)LocalAlloc(LPTR,sizeof(BITMAPINFOHEADER)+sizeof(RGBQUAD)*(1<<cClrBits));
	else
		pbmi=(PBITMAPINFO)LocalAlloc(LPTR,sizeof(BITMAPINFOHEADER));
	pbmi->bmiHeader.biSize=sizeof(BITMAPINFOHEADER);
	pbmi->bmiHeader.biWidth=bmp.bmWidth;
	pbmi->bmiHeader.biHeight=bmp.bmHeight;
	pbmi->bmiHeader.biPlanes=bmp.bmPlanes;
	pbmi->bmiHeader.biBitCount=bmp.bmBitsPixel;
	if(cClrBits<24)
		pbmi->bmiHeader.biClrUsed=(1<<cClrBits);
	pbmi->bmiHeader.biClrImportant=BI_RGB;
	pbmi->bmiHeader.biSizeImage=((pbmi->bmiHeader.biWidth*cClrBits+31)&~31)*pbmi->bmiHeader.biHeight;
	pbmi->bmiHeader.biClrImportant=0;
	return(pbmi);
}