Click here to Skip to main content
Click here to Skip to main content

Width of text in italic font

, 23 Aug 2006
Rate this:
Please Sign up or sign in to vote.
Shows an alternative to GetCharABCWidths and GetCharABCWidthsFloat.

Introduction

Our purpose is to measure accurately the width of text written in italic font.

Using the code

The GetTextExtentPoint32 Win32 API function or the DrawText Win32 API function with the DT_CALCRECT flag, will -not- tell us the correct width of text in italic font, only the calculated height is correct. For most of the italic fonts, using these two functions, the calculated width is too narrow and the displayed text looks right-trimmed.

We could try using the GetCharABCWidths or GetCharABCWidthsFloat Win32 API functions. These functions will give us information about the underhang and the overhang of each character of the text we're interested in.

Please check these MSDN articles for more details about using the underhang and overhang values:

This updated version of the EXE includes a new checkbox, to see how adding the 'overhang of the last character' will help getting a more accurate result.

However, in this article, I am suggesting another approach:

  1. Paint the text in black colour, in a memory device context filled with white colour, like this:
    SIZE sizeText;
    //Calculate the width of the text, by using the classic method
    GetTextExtentPoint32(hDCMem,szText,lstrlen(szText),&sizeText);
    
    //Calculate the width of the last character, as suggested by 'oupoi'
    SIZE sizeLastCharacter;
    GetTextExtentPoint32(hDCMem,&szText[-1+lstrlen(szText)],1,&sizeLastCharacter);
    
    //Set a bounding rectangle wide enough to fit the painted text
    RECT rect={0,0,sizeText.cx+sizeLastCharacter.cx,sizeText.cy};
    
    //Fill the background with white colour then paint the text in black colour
    FillRect(hDCMem,&rect,(HBRUSH)GetStockObject(WHITE_BRUSH));
    DrawText(hDCMem,szText,-1,&rect, 
             DT_LEFT|DT_TOP|DT_SINGLELINE|DT_NOPREFIX);
  2. Then, scan the colour of the pixels in the memory device context, from right-to-left, like this:
    int iXmax=0;
    BOOL bFound=FALSE;
    for(int x=rect.right-1; x>=0 && !bFound; x--)
    {
       for(int y=0; y<=rect.bottom-1 && !bFound; y++)
       {
          COLORREF rgbColor=GetPixel(hDCMem,x,y);
          if(rgbColor!=RGB(255,255,255))
          {
              //found a non-white pixel, save the horizontal position 
              //and exit the loops. Job finished.
              iXmax=x;
              bFound=TRUE;
          }
       }
    }
    
    //this is the width of the text painted in italic font!
    LONG lWidthOfText=iXmax+1;//+1 because we use 0-based indexes

A few comments:

  • Painted text can be narrower than text calculated with GetTextExtentPoint32. See, for example, Verdana 12 Italic.
  • In a dialog box, the edit controls have left/right and up/down margins to take into account. I have not used edit controls in this sample.
  • In a dialog box, the label controls seem to be +1 pixel wider, unless the SS_SIMPLE style is used. See the image below.

History

  • Version 1.0 [July 23, 2006] - Created.
  • Version 1.1 [August 6, 2006] - New checkbox to see how adding the 'overhang of the last character' to the classic method of calculating the text width will help getting a more accurate result.

    Like this:

    SIZE sizeText; 
    GetTextExtentPoint32(hDCMem, szText, lstrlen(szText), &sizeText);
    LONG lWidthOfText= sizeText.cx;
                        
    ABCFLOAT WidthsABC[256];
    GetCharABCWidthsFloat(hDCMem, 0, 255, WidthsABC); 
    
    // overhang of the last character
    double dOverhangTrailing = WidthsABC[szText[lstrlen(szText)-1]].abcfC;
    
    if(dOverhangTrailing<0)
    {
       //if the overhang is negative then adjust 
       //the calculated width of the text
       lWidthOfText-=dOverhangTrailing;
    }

    But as already mentioned above, this article is suggesting another method, which doesn't require using any of these underhang and overhang values.

  • Version 1.2 [August 17, 2006] - Adjustment to the right-to-left pixel colour scanning algorithm.

    Set the right-limit of the bounding rectangle to be scanned to just 'sizeText.cx+widthOfTheLastCharacter', as suggested by 'oupoi'.

    We now also have a new checkbox to test if using the Mihai Nita's trick will help getting a faster calculation and at the same time, of course, an accurate result.

    Unless I've made a mistake somewhere, I'm not satisfied by the precision of the result by using the Mihai Nita's trick.

    Like this:

    //fill with white
    FillRect(hDCMem,&rect,(HBRUSH)GetStockObject(WHITE_BRUSH));
    
    // Added this by Mihai Nita - August 17, 2006
    // trick, set text background colour to black, before painting!
    SetBkColor(hDCMem,RGB(0,0,0)); 
    
    //reality shows that DrawText fails to properly 
    //paint the surrounding rectangle (??)
    DrawText(hDCMem,szText,-1, &rect, 
             DT_LEFT|DT_TOP|DT_SINGLELINE|DT_NOPREFIX);
    
    int iXmax=0;
    BOOL bFound=FALSE;
    int iYmed=(rect.bottom+rect.top)/2; // middle
    
    for(int x=rect.right-1;x>=0 && !bFound ;x--)
    {
      COLORREF rgbColor=GetPixel(hDCMem,x,iYmed);
      if(rgbColor!=RGB(255,255,255))
      {
        iXmax=x;
        bFound=TRUE;
      }
    }

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

Share

About the Author

Alexandru Matei
Web Developer
Romania Romania
No Biography provided

Comments and Discussions

 
SuggestionStill not a hundred percent accurate PinmemberDai Fei10-Mar-14 7:05 
GeneralAbout text width [modified] PinmemberKsuyong19-May-08 3:06 
GeneralRe: About text width PinmemberAlexandru Matei19-May-08 3:18 
GeneralInteresting Pinmemberkjsfuture16-May-08 19:20 
GeneralHelp me Pinmemberkjsfuture16-May-08 18:19 
GeneralRe: Help me [modified] PinmemberAlexandru Matei16-May-08 21:22 
GeneralInteresting Pinmemberwaldermort24-Aug-06 23:33 
GeneralNice, but... Pinmemberoupoi16-Aug-06 19:18 
GeneralRe: Nice, but... PinmemberAlexandru Matei16-Aug-06 21:40 
GeneralIt seems quite inefficient PinmemberMihai Nita16-Aug-06 10:41 
GeneralRe: It seems quite inefficient [modified] PinmemberAlexandru Matei16-Aug-06 11:14 
GeneralRe: It seems quite inefficient [modified] PinmemberAlexandru Matei16-Aug-06 12:37 
GeneralRe: It seems quite inefficient PinmemberMihai Nita16-Aug-06 23:56 
GeneralRe: It seems quite inefficient [modified] PinmemberAlexandru Matei17-Aug-06 0:33 
GeneralRe: It seems quite inefficient PinmemberMihai Nita20-Aug-06 11:40 
Alexandru Matei wrote:
I've found a few counterexamples that do not work properly. Please try these strings:
'k6' or 'c6' or 'a6' or 'c7' or 'c9' or 'x9' or 'c5' or 'v5' with Tahoma and Microsoft Sans Serif and Lucida Console (italic, of course).

 
It works ok in my tests. It would help if you post your test application (in fact, others also suggested this).
 
Alexandru Matei wrote:
I don't understand what you're talking about here. I've checked the MSDN articles and the overhang of the last character is quite useful.

Nope. The MSDN articles are not the Bible.
 
All GetCharABC... familty of functions are bad for internationalization.
You should NEVER compute the width of strings based on width of stand-alone characters.
 
Example: the Romanian character "tz" can be represented as one character (U+021B, latin small letter t with comma below) or as t with combining comma below (U+0074 U+0326).
But in the proposed alghorithm, the last char is the combining character, with width ZERO.
Same kind of problems where the the characters change shape depending on the context (what is before or after).
 
The t with comma is just an example to help understand the issues, the typical usa in Romanian is with U+021B (typical, but not mandatory Smile | :) )
But there are scripts where combining characters and complex shaping are the norm (Arabic, Vietnamese, Thai, most Hindic scripts).

GeneralRe: It seems quite inefficient [modified] PinmemberAlexandru Matei20-Aug-06 19:58 
GeneralDT_CALCRECT and GetCharABCWidths() [modified] Pinmemberbob1697230-Jul-06 19:16 
GeneralRe: DT_CALCRECT and GetCharABCWidths() [modified] PinmemberAlexandru Matei30-Jul-06 22:38 
GeneralRe: DT_CALCRECT and GetCharABCWidths() [modified] Pinmemberbob1697231-Jul-06 4:14 
GeneralRe: DT_CALCRECT and GetCharABCWidths() [modified] PinmemberAlexandru Matei31-Jul-06 9:01 
GeneralRe: DT_CALCRECT and GetCharABCWidths() Pinmemberbob1697231-Jul-06 10:19 
GeneralRe: DT_CALCRECT and GetCharABCWidths() PinmemberAlexandru Matei31-Jul-06 10:20 
GeneralUsing DT_CALCRECT PinmemberJan Rodriguez25-Jul-06 15:10 
GeneralRe: Using DT_CALCRECT [modified] PinmemberAlexandru Matei25-Jul-06 20:59 
GeneralRe: Using DT_CALCRECT PinmemberJan Rodriguez25-Jul-06 22:07 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Terms of Use | Mobile
Web04 | 2.8.141216.1 | Last Updated 23 Aug 2006
Article Copyright 2006 by Alexandru Matei
Everything else Copyright © CodeProject, 1999-2014
Layout: fixed | fluid