Fast way to display large images

Hi gurus!!

I am working with a large images (280 Mb aprox) in BMP format.

I can print a image on DC using StretchDIBits and it works fine.

I want to save in a buffer the content of the DC (after the image was printed) because if part of the dialog is invalidate (down or move the dialog) I can print again in small time.

What is the best way?

Thanks in advance!!!

Hi!

Perhaps the ask is not very clear...


Step 1.- Read BMP file:
IN .H FILE:

Code:

---

class CTrasformaDlg : public CDialog
{
// Construcción
public:
    CTrasformaDlg(CWnd* pParent = NULL);    // Constructor estándar

// Datos del cuadro de diálogo
    enum { IDD = IDD_TRASFORMA_DIALOG };

    protected:
    virtual void DoDataExchange(CDataExchange* pDX);    // Compatibilidad con DDX/DDV


// Implementación
protected:
    HICON m_hIcon;

    // Funciones de asignación de mensajes generadas
    virtual BOOL OnInitDialog();
    afx_msg void OnSysCommand(UINT nID, LPARAM lParam);
    afx_msg void OnPaint();
    afx_msg HCURSOR OnQueryDragIcon();
    DECLARE_MESSAGE_MAP()
public:
    afx_msg void OnDestroy();
    afx_msg void OnBnClickedButtonLoadbmp();
   
    CString szBmpFile;
    CString szEcwFile;

    HWND hndWnd;
    // BMP Completo

    BYTE *pBits;
    BITMAPINFOHEADER infoHeader;
    int nBitsPixel, nHeight, nPlanos, nWidth, nImgSize;
    CRect rBmp;
    HDC hDC;
};

---

IN .CPP FILE:

Code:

---

void CTrasformaDlg::OnBnClickedButtonLoadbmp()
{
    // TODO: Agregue aquÃ* su código de controlador de notificación de control
    CFileDialog fDlg(TRUE, _T("*.bmp"), 0, 4|2, _T("Ficheros BMP (*.bmp)|*.bmp||"), this);
    fDlg.DoModal();
    szBmpFile = fDlg.GetPathName();

    if(szBmpFile == "") return; 

    char sNombre[500];
    WideCharToMultiByte(CP_ACP, NULL, szBmpFile, -1, sNombre, 500, NULL, NULL);

    FILE *pf = fopen(sNombre, "rb");

    nWidth = 0;
    nHeight = 0;
    nBitsPixel = 0;
    nPlanos = 0;
    int nOffsetImg = 0;
    nImgSize = 0;

    fseek(pf, 10L, SEEK_SET);
    fread(&nOffsetImg, 4, 1, pf);
    fseek(pf, 34L, SEEK_SET);
    fread(&nImgSize, 4, 1, pf);

    fseek(pf, 18L, SEEK_SET);
    fread(&nWidth, 4, 1, pf);
    fseek(pf, 22L, SEEK_SET);
    fread(&nHeight, 4, 1, pf);       

    fseek(pf, 26L, SEEK_SET);
    fread(&nPlanos, 2, 1, pf);
    fseek(pf, 28L, SEEK_SET);
    fread(&nBitsPixel, 2, 1, pf);   

    pBits = (BYTE *) malloc(nImgSize);
    memset(pBits, 0, nImgSize);

    fseek(pf, nOffsetImg, SEEK_SET);
    fread(pBits, nImgSize, 1, pf);

    fclose(pf);
 
    hndWnd = ::GetDlgItem(this->GetSafeHwnd(), IDC_STATIC_IMG);           
    ::GetClientRect(hndWnd, &rBmp);

    memset(&infoHeader, 0, sizeof(BITMAPINFOHEADER));
    infoHeader.biBitCount = nBitsPixel;
    infoHeader.biCompression = BI_RGB;
    infoHeader.biHeight = nHeight;
    infoHeader.biPlanes = nPlanos;
    infoHeader.biWidth = nWidth;
    infoHeader.biSize = sizeof(BITMAPINFOHEADER);   
    infoHeader.biSizeImage = nImgSize;     

    OnPaint();
}

void CTrasformaDlg::OnPaint()
{
    if (IsIconic())
    {
        CPaintDC dc(this); // Contexto de dispositivo para dibujo

        SendMessage(WM_ICONERASEBKGND, reinterpret_cast<WPARAM>(dc.GetSafeHdc()), 0);

        // Centrar icono en el rectángulo de cliente
        int cxIcon = GetSystemMetrics(SM_CXICON);
        int cyIcon = GetSystemMetrics(SM_CYICON);
        CRect rect;
        GetClientRect(&rect);
        int x = (rect.Width() - cxIcon + 1) / 2;
        int y = (rect.Height() - cyIcon + 1) / 2;

        // Dibujar el icono
        dc.DrawIcon(x, y, m_hIcon);
    }
    else
    {       
        CDialog::OnPaint();       
    }
    Dibuja();
}

---

Step 2.- Print the image into DC:

Code:

---

void CTrasformaDlg::Dibuja(void) {
    hDC = ::GetDC(hndWnd);   
    BITMAPINFO bInfo;
    memset(&bInfo, 0, sizeof(BITMAPINFO));
    bInfo.bmiHeader = infoHeader;

    ::SetStretchBltMode(hDC, HALFTONE);
    int nLines = ::StretchDIBits(
        hDC,
        0,
        0,
        rBmp.Width(),
        rBmp.Height(),
        0,
        0,
        rBmp.Width(),
        rBmp.Height(),
        (void **)pBits,
        &bInfo,
        DIB_RGB_COLORS,SRCCOPY);
    ::DeleteDC(hDC);
}

---

....

Now I have the image loaded in memory and printed in the window. I want to save the printed image in a buffer like a primary image was saved.

It is quite clear?:confused::confused:


Thanks!!

You have already done half of the work I think. Something like this will do the trick.

Code:

---

CDC pDC = GetDC();
CRect Rect;
GetWindowRect(&Rect);

CDC MemDC;
MemDC.CreateCompatibleDC(pDC);
CBitmap m_Bitmap;
m_Bitmap.CreateCompatibleBitmap(pDC,Rect.Width(),Rect.Height());
CBitmap *pOldBmp = MemDC.SelectObject(&m_Bitmap);
MemDC.BitBlt(0,0,Rect.Width(),Rect.Height(),pDC,Rect.left,Rect.top,SRCCOPY);
MemDC.SelectObject(pOldBmp);

now m_Bitmap holds the image of the pDC.

BITMAP myBitmap;

m_Bitmap.GetBitmap(&myBitmap);

myBitmap holds the image structure. and you're done.

---

That's a really huge image. Odds are, you don't need to see the whole thing at once, or if you do, you'll be zoomed out.

This suggests that mipmapping the image and/or breaking it up into tiles may allow you to redraw it more quickly.