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An Image Decoder Based on IImgCtx

, 25 May 2004
This article shows how to decode image with IImgCtx interface provided by IE
// WndImgCtx.cpp : implementation file
//

#include "stdafx.h"
#include "ImgViewer.h"
#include "WndImgCtx.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

HBITMAP GetBitmapFromFile(LPCTSTR pszFilename)
{
	HBITMAP hRet = NULL;

	CoInitialize( NULL );
	
	CWndImgCtx wndImg;
	RECT rectWnd;
	rectWnd.left = rectWnd.top = 0;
	rectWnd.right = rectWnd.bottom = 100;
	wndImg.Create(NULL, "WndImgCtx", WS_OVERLAPPED, rectWnd, AfxGetApp()->m_pMainWnd, 1);

	if (IsWindow(wndImg.m_hWnd))
	{
		HRESULT hr = wndImg.StartDecode(pszFilename);
		if (SUCCEEDED(hr))
		{
			// make ure the message pump can get a message every 50 ms
			UINT iTimer = wndImg.SetTimer(1, 50, NULL);

			// use message pump to drive decode process
			BOOL bGet = FALSE;
			MSG msg;
			while (!bGet)
			{
				while (::PeekMessage(&msg, (HWND) NULL, 0, 0, PM_REMOVE))
				{
					if ( msg.message==WM_QUIT )
					{
						::PostQuitMessage(-1);
						bGet = TRUE;
						break;
					}
					else if (wndImg.CheckState())
					{
						bGet = TRUE;
						break;
					}
					else if (!AfxGetApp()->PreTranslateMessage(&msg))
					{
						::TranslateMessage(&msg);
						::DispatchMessage(&msg);
					}
				}
			}

			if (bGet)
				hRet = wndImg.GetBitmap();

			wndImg.KillTimer(iTimer);
		}
	}

	wndImg.DestroyWindow();

	CoUninitialize();

	return hRet;
}

/////////////////////////////////////////////////////////////////////////////
// CWndImgCtx

CWndImgCtx::CWndImgCtx()
{
	m_pImgCtx = NULL;
    m_hPal = NULL;
}

CWndImgCtx::~CWndImgCtx()
{
}


BEGIN_MESSAGE_MAP(CWndImgCtx, CWnd)
	//{{AFX_MSG_MAP(CWndImgCtx)
	ON_WM_DESTROY()
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()


/////////////////////////////////////////////////////////////////////////////
// CWndImgCtx message handlers

void CWndImgCtx::OnDestroy() 
{
	CWnd::OnDestroy();
	
	// TODO: Add your message handler code here
    if ( m_pImgCtx )
        m_pImgCtx->Release();
}

const char c_szFilePro[] = "file://";

void CreateUrlFromPath(LPCTSTR pszPath, WCHAR* pszUrl, int cchWideChar)
{
    CHAR szURL[MAX_PATH + sizeof(c_szFilePro)];

	lstrcpy(szURL, c_szFilePro);
	lstrcat(szURL, pszPath);
	for (char* p = szURL; *p; p++)
		if (*p == '\\') *p = '/';

	MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, szURL, -1, pszUrl, cchWideChar);
}

HRESULT CWndImgCtx::StartDecode(LPCTSTR pszFilename)
{
    if (!pszFilename)
        return E_INVALIDARG;

    WCHAR szURL[MAX_PATH + sizeof(c_szFilePro)];
    CreateUrlFromPath(pszFilename, szURL, sizeof(szURL)/sizeof(WCHAR));
	
    HRESULT hr = CoCreateInstance(CLSID_IImgCtx, NULL, CLSCTX_INPROC_SERVER, IID_IImgCtx, (LPVOID*)&m_pImgCtx);
    if (SUCCEEDED(hr))
        hr = m_pImgCtx->Load(szURL, 0);

    return hr;
}

BOOL CWndImgCtx::CheckState()
{
	BOOL bRet = FALSE;

    if ( m_pImgCtx )
    {
		HRESULT hr;
		SIZE  sizeImage;
		ULONG ulState;

        hr = m_pImgCtx->GetStateInfo(&ulState, &sizeImage, FALSE);

        if (SUCCEEDED(hr))
        {
			if ((ulState & IMGLOAD_COMPLETE) || (ulState & IMGLOAD_STOPPED) || (ulState & IMGLOAD_ERROR))
			{
				m_pImgCtx->GetPalette(&m_hPal);
				m_sizeImage = sizeImage;
				
				bRet = TRUE;
			};
        }
    }

	return bRet;
}

void CWndImgCtx::OnDraw(HDC hdcDraw)
{
    SetMapMode(hdcDraw, MM_TEXT);

    if (m_hPal)
    {
        SelectPalette(hdcDraw, m_hPal, TRUE);
        RealizePalette(hdcDraw);
    }

    if (m_pImgCtx)
		m_pImgCtx->Draw(hdcDraw, &CRect(0, 0, m_sizeImage.cx, m_sizeImage.cy));
}

HBITMAP CWndImgCtx::GetBitmap()
{
	HBITMAP hRet = NULL;

	if (m_pImgCtx == NULL)
		return hRet;

	HDC hScrDC = CreateDC("DISPLAY", NULL, NULL, NULL);
	if (hScrDC)
	{
		HDC hMemDC = CreateCompatibleDC(hScrDC); 
		if (hMemDC)
		{
			// create a bitmap compatible with the screen DC 
			HBITMAP hBitmap = CreateCompatibleBitmap(hScrDC, GetImageWidth(), GetImageHeight());
			if (hBitmap)
			{
				// select new bitmap into memory DC 
				HBITMAP hOldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap);

				//CDC::FillSolidRect();
				{
					RECT rect;
					rect.left = rect.top = 0;
					rect.right = GetImageWidth();
					rect.bottom = GetImageHeight();
					::SetBkColor(hMemDC, GetSysColor(COLOR_WINDOW));
					::ExtTextOut(hMemDC, 0, 0, ETO_OPAQUE, &rect, NULL, 0, NULL);
				}

				OnDraw(hMemDC);

				// select the old bitmap back into memory DC and get handle to bitmap
				hRet = (HBITMAP)SelectObject(hMemDC, hOldBitmap);

				SetBitmapDimensionEx(hRet, GetImageWidth(), GetImageHeight(), NULL);
			}

			DeleteDC(hMemDC); 
		}
	}
	DeleteDC(hScrDC);

	return hRet;
}

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strnghrs
Web Developer
China China
No Biography provided

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