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CWebImageDC

, 27 Aug 2000
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Provides a memory based DC into which an image may be drawn using standard GDI calls.

Sample Image - WebImageDC.jpg

Introduction

Derived from the MFC class CDC, this class provides a memory based DC into which an image may be drawn using standard GDI calls. The resulting image may then be saved as either a PNG file or written to a CMemFile for insertion into a CHttpStream (a demonstration of this is included at the bottom of this article).

Usage

BOOL Create(CSize &pImageSize);

As with many MFC classes, CWebImageDC requires a two step creation. After being instantiated, the Create method must be called once to generate the bitmap. The CSize parameter indicates the width and height of the resulting image in pixels. If you will not be drawing over the entire bitmap, you should probably then call the Erase method (see below).

BOOL SaveAsPNG(
    CString &pFileName,
    BOOL pInterlaced = TRUE,
    BOOL pTransparent = FALSE,
    COLORREF pTransparentColor = RGB(255,255,255));

Saves the bitmap in PNG format to the file specified in the pFileName parameter. The optional control parameters will determine whether the resulting file is interlaced, and whether it has one of its colors set to transparent (and which color that is).

BOOL StreamAsPNG(
    CMemFile * pMemFile,
    BOOL pInterlaced = TRUE,
    BOOL pTransparent = FALSE,
    COLORREF pTransparentColor = RGB(255,255,255));

Writes the bitmap in PNG format to the CMemFile specified in the pMemFile parameter. The buffer associated with the MemFile can then be accessed using the .Detach() method and can be sent to a CHttpStream using the .Write() method. See the source code in the Bar example below for an example of this technique.

void Erase(COLORREF pColor);

Fills the entire bitmap with the color specified.

Sample

Sample Image

The bar chart above was generated using the CWebImageDC in an ISAPI plug-in which takes a parameter list describing a single bar in a bar chart, and returns an HTTP stream which contains the raster image of the described bar in PNG format.

Usage:

The plug-in is used as follows:

<img src="/scripts/bar.dll?Draw¶meters ">

where parameters have the form:

ww,hh,bc,dc,rr,vv,ss,sn,sc...

The parameters are as follows:

  • ww = width in pixels
  • hh = height in pixels
  • bc = background color in RRGGBB format (hex)
  • dc = default color
  • label = the column label
  • rr = range for the bar
  • vv = value of the bar
  • ss = number of sigmas (divisions)
  • sn,sc = comma separated list of sigmas and colors

Note: colors are in the form RRGGBB in hex from 00 to FF

Example:

<img src="/scripts/bar.dll?Draw&30,300,FFFFFF,
   0000FF,Oct,40.0,36,3,20,00FF00,26,FFFF00,30,FF000">

would result in the following:

Bar Image

A series of these can easily be used to generate a bar chart like the one shown earlier, within an ASP page.

Acknowledgements

This class uses the PNG and ZLIB libraries provided by the PNG Working Group and the HIPNG provided by Alan Algustyniak. Thanks very much for the great libraries.

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

Randy More

United States United States
No Biography provided

Comments and Discussions

 
Generalstream problem PinmemberGuigaRJ6-Jan-05 5:11 
General256 colors workaround with CImage PinmemberKurt Muellner18-Dec-02 22:52 
GeneralDoesn't work ISAPI test PinmemberMarkus Julian3-Dec-02 14:33 
GeneralWorkaround for 256 color mode Pinsussbushi17-Sep-00 23:58 
Questionhow to get around build errors PinsussGee25-Aug-00 5:02 
Generalsaving/printing gdi calls PinsussCameron Ditty8-Aug-00 10:17 
GeneralI can't build it. Help me PinsussAlexey28-Jul-00 7:39 
Generalcontact with Author Pinsussbushi26-Jul-00 22:01 
GeneralRe: contact with Author PinsussErnesto Perales Soto28-Jul-00 6:21 
GeneralTranparency didn't work! PinsussFloriano23-Jul-00 5:27 
GeneralRe: Tranparency didn't work! Pinmemberboothr28-May-01 9:44 
GeneralMissing deflate.h PinsussPaul22-Jul-00 23:24 
General1. Problem with ISAPI ext. 2.StdAfx.h missing Pinsussbushi21-Jun-00 4:19 
GeneralRe: 1. Problem with ISAPI ext. 2.StdAfx.h missing Pinsussbushi21-Jun-00 4:24 
Generalcancel it!!! Pinsussbushi21-Jun-00 7:38 
Generallinking errors in vc6 PinsussHenry Kho13-Apr-00 22:45 
Generalassertion error fix(temporary?) Pinsussjohn11-Apr-00 8:51 
GeneralRe: assertion error fix(temporary?) Pinsussbushi21-Jun-00 7:33 
GeneralFIX FOR MEMORY LEAKS! PinsussRKM11-Apr-00 8:02 
Generalassertion error Pinsussjohn11-Apr-00 7:47 
GeneralRe: assertion error PinsussRKM11-Apr-00 7:53 
General256 color mode PinsussErnesto Perales Soto7-Mar-00 14:43 
GeneralRe: 256 color mode PinsussRKM11-Apr-00 7:52 
GeneralAnswer to DEFLATE.H PinsussAaron Manuel5-Feb-00 19:21 
GeneralRe: Answer to DEFLATE.H PinsussAnonymous11-Jul-02 12:33 

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