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Bypass Graphics.MeasureString limitations

, 22 Apr 2003
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This sample code computes the width of the string, as drawn by Graphics.DrawString

Sample Image - measurestring.gif

Introduction

Graphics.MeasureString can be used to compute the height and width of a text string. Often, however, the dimensions returned do not match the size of what gets drawn on screen when calling Graphics.DrawString. The red box above shows the dimensions returned by Graphics.MeasureString, which is about an em too wide...

The differences between what is computed and what is really drawn on the screen are related to how GDI+ computes its widths when using hinting and antialiasing. Here are the  gory details. A known work-around is to make GDI+ display its string antialiased, in which case the measured width matches the displayed result. If you want to draw standard strings (to match the GUI appearance, for instance), you are left out.

First, naive solution

The code I present here can be inserted into any class which needs to compute the real width of a string (shown by the yellow background above). The trick I use to compute the real string width is to ask GDI+ to draw the string into a bitmap and then find the position of the last character by reading back the pixels. A few optimisations ensure that this gets done as fast as possible (small bitmap, few pixels).

static public int MeasureDisplayStringWidth(Graphics graphics, string text,
                                            Font font)
{
    const int width = 32;

    System.Drawing.Bitmap   bitmap = new System.Drawing.Bitmap (width, 1, <BR>                                                                graphics);
    System.Drawing.SizeF    size   = graphics.MeasureString (text, font);
    System.Drawing.Graphics anagra = System.Drawing.Graphics.FromImage(bitmap);

    int measured_width = (int) size.Width;

    if (anagra != null)
    {
        anagra.Clear (Color.White);
        anagra.DrawString (text+"|", font, Brushes.Black,
                           width - measured_width, -font.Height / 2);

        for (int i = width-1; i >= 0; i--)
        {
            measured_width--;
            if (bitmap.GetPixel (i, 0).R != 255)    // found a non-white pixel ?
                break;
        }
    }

    return measured_width;
}

That's all, folks. Right-to-left scripts won't probably work with this piece of code.

Another solution...

It is also possible to get the accurate string geometry by using MeasureCharacterRanges, which returns a region matching exactly the bounding box of the specified string. This is faster and more elegant than the first solution I posted on CodeProject.

static public int MeasureDisplayStringWidth(Graphics graphics, string text,
                                            Font font)
{
    System.Drawing.StringFormat format  = new System.Drawing.StringFormat ();
    System.Drawing.RectangleF   rect    = new System.Drawing.RectangleF(0, 0,
                                                                  1000, 1000);
    System.Drawing.CharacterRange[] ranges  = <BR>                                       { new System.Drawing.CharacterRange(0, 
                                                               text.Length) };
    System.Drawing.Region[]         regions = new System.Drawing.Region[1];

    format.SetMeasurableCharacterRanges (ranges);

    regions = graphics.MeasureCharacterRanges (text, font, rect, format);
    rect    = regions[0].GetBounds (graphics);

    return (int)(rect.Right + 1.0f);
}

Post Script

Both functions only work with non-empty strings. The second solution will strip the trailing spaces; the first solution will take them in account. Choose the one which best fits your needs

License

This article, along with any associated source code and files, is licensed under The GNU Lesser General Public License (LGPLv3)

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About the Author

Pierre Arnaud
Web Developer
Switzerland Switzerland

Pierre Arnaud got a Ph.D. in computer science at the Swiss Federal Institute of Technology; he currently works both as an independent contractor on hardware and software projects at OPaC bright ideas and as a senior software designer at EPSITEC.

Pierre was a key contributor to the Smaky computer, a real time, multitasking system based on the Motorola 680x0 processor family.

Now, Pierre works on his spare time for the Creative Docs .NET project: it is a vector based drawing and page layout software based on .NET and AGG.


Comments and Discussions

 
AnswerRe: Is this a bug? PinmemberPierre Arnaud18-May-05 19:43 
GeneralVery helpful Pinsusssmushkat4-Mar-05 17:50 
GeneralNumber of lines text wrapped. Pinmemberjohannf21-Feb-05 6:16 
GeneralC code Pinmemberacostein4-Feb-05 18:46 
GeneralA (possible) imrovement Pinmemberxaverbirrer5-May-05 4:48 
Generalhighlighting Pinmembersreejith ss nair27-Dec-04 21:28 
QuestionWhat about Height Problem? PinmemberSameers (theAngrycodeR )11-Jul-04 12:57 
Questionrect.Right + 1.0f? Pinmemberimessvb3-Jun-04 22:02 
I dont see why you need to add 1 there. I found that a bounding rectangle of width 501 pixels just enough to print 67 characters with courier 9 has a resulting rectangle of Left:2,Width:499
 
btw, this method doesn't measure string width right all the time, I mean, using this method on a 62-char string and a 10-char string (both with same monospace font) doesn't give the same char width...
GeneralParameter PinmemberRatee29-May-04 19:33 
GeneralRe: Parameter PinmemberPierre Arnaud29-May-04 22:19 
GeneralA little correction Pinmemberedx_fa25-Jan-04 11:52 
GeneralRe: A little correction PinmemberPierre Arnaud25-Jan-04 18:43 
GeneralPoor PinsussGensi22-Aug-03 2:26 
GeneralRe: Poor PinmemberPierre Arnaud22-Aug-03 2:33 
GeneralRe: Poor PinsussAnonymous22-Aug-03 6:32 
GeneralRe: Poor PinsussGensi22-Aug-03 6:33 
GeneralIts not Poor, its helpful Pinmemberxaverbirrer5-May-05 3:30 
GeneralGREAT Pinsussjlau13-Mar-03 22:05 
GeneralRe: GREAT PinmemberKenneth Kryger Sørensen21-Jun-04 3:32 
Generalnon integer font size Pinmembercompumaster12-Mar-03 11:42 
GeneralRe: non integer font size PinmemberPierre Arnaud13-Apr-03 20:47 
GeneralA better way to measure strings. PinmemberAnonymous20-Jun-02 5:24 
GeneralRe: A better way to measure strings. Pinmemberdog_spawn23-Apr-03 10:25 
GeneralRe: A better way to measure strings. Pinmembernetmar7-Jul-04 22:19 
Generalquestion Pinmemberreal name15-Apr-02 2:30 

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