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PNGView

, 7 Sep 2005
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Load and display PNG files in MFC.

Sorry, it should have been PNGView.jpg

Introduction

This is a very simple approach to display PNG files in MFC. Two common libraries provide the needed functionality: zlib and libpng. These libraries are included in the source file.

Background

I had been searching the net for a really simple PNG example for a whole while. But all I found were C files that contained more preprocessor directives than keywords. I don't like preprocessor directives so I've written this example. It uses only one class to do the whole stuff.

Using the code

At first:

You might have to upgrade your include-folder settings, because libpng wants to know where your zlib.h is located. After you have unzipped the downloaded archive, you can find this file in the ...\zlib\code\ folder.

The FileOpen handler:

This chunk of code works off both reading and showing the PNG file:

// create temporary object
PngImage png;

// import png file
if ( png.load(dlg.GetPathName()) )
{
    // get size
    int width  = png.getWidth();
    int height = png.getHeight();

    // get blue, green, red and alpha values
    unsigned char* data = png.getBGRA();

    // free memory first
    if (m_bitmap) delete m_bitmap;
    if (m_visible) delete m_visible;

    // create a CBitmap to display
    m_bitmap = doCreateCompatibleBitmap(width, height, data, this);

    // used to speed up OnPaint()
    m_visible = doZoomBitmap(m_bitmap, this);

    // request graphical update
    Invalidate();
    UpdateWindow();
}

History

Version 1.3

Added:

  • Reading 1, 2 and 4 bit monochrome images.
  • Reading 1, 2 and 4 bit monochrome images with transparency.
  • Reading images that use a palette.

Version 1.2

Changed:

  • Displaying the CBitmap object got faster.

Version 1.1

Not submitted

Version 1.0

Added:

  • Reading 8-bit RGB images.
  • Reading 8-bit RGB images with transparency.
  • Reading 8-bit monochrome images.
  • Reading 8-bit monochrome images with transparency.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Achim Klein
Web Developer
Germany Germany
No Biography provided

Comments and Discussions

 
GeneralWhy not use CPngImage in mfc? it's convinience and efficient Pinmemberecjtuxsyuan13-Nov-10 6:27 
GeneralRe: Why not use CPngImage in mfc? it's convinience and efficient PinmemberNorbert Bons1-Sep-14 4:14 
QuestionHow to display a transparent PNG? PinmemberNvng YA25-Apr-08 6:57 
AnswerRe: How to display a transparent PNG? Pinmemberbenjamin2311-May-09 1:53 
General16bits (hicolor support) + license question Pinmembertcm199825-Sep-06 5:32 
I've noticed that the viewer doesn't support displaying while windows is set to 16 bits color mode). Since I wanted my program to display correct in this colormode too, I've hacked in some 16bits support. I know it's quick and VERY dirty but I still tought I'd share it:
 
The change is in the inner for-loop within PngImage::doConvertRGB8.
 
if (!m_b16bitColor){
bgra[pos++] = row_pointers[i][j + 2]; // blue
bgra[pos++] = row_pointers[i][j + 1]; // green
bgra[pos++] = row_pointers[i][j]; // red
bgra[pos++] = 0; // alpha
}
else{
unsigned short col16R;
unsigned short col16G;
unsigned short col16B;
col16R = (row_pointers[i][j]*31)/255;
col16G = (row_pointers[i][j + 1]*63)/255;
col16B = (row_pointers[i][j + 2]*31)/255;
unsigned short col16 = col16B + (col16G << 5) + (col16R << 11);
bgra[pos++] = col16 & 0xFF;
bgra[pos++] = (col16 & 0xFF00)>>8;
}

 
About the license ... I'd like my program (accat / www.layer1.net/acww) to become open source (GPL license). Since I've used the png image code, can I do that ? Anything specific I should put in the header of the file(s) ?
GeneralRe: 16bits (hicolor support) + license question PinmemberAchim Klein3-Oct-06 2:14 
Questionincorrect source Pinmemberjalal_haddad1-May-06 8:33 
AnswerRe: incorrect source PinmemberAchim Klein2-Jun-06 3:14 
AnswerRe: incorrect source Pinmemberheshule22-Mar-07 22:36 
GeneralCrashes under Win32 PinmemberAchim Klein10-Sep-05 3:27 

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