sec-gdkfont.html

gtk 开发手册和参考文档。 包括gtk glib gdk等

        </h2>
        <p>
          To use a font, you typically need detailed information
          about its <i class="FIRSTTERM">metrics</i>. Font metrics
          are used to position characters with respect to one
          another, and to determine the size of strings rendered in
          the font. The most fundamental metrics are the <i class= 
          "FIRSTTERM">ascent</i> and <i class="FIRSTTERM">
          descent</i> of the font. Text is placed on a <i class= 
          "FIRSTTERM">baseline</i>; the baseline is like a rule on
          a sheet of notebook paper. The bottom of each character
          touches the baseline. Some characters (such as lowercase
          "p" and "y") extend below the baseline. A font's <i
          class="FIRSTTERM">descent</i> is the maximum distance
          below the baseline reached by its characters. Its <i
          class="FIRSTTERM">ascent</i> is the maximum distance
          above the baseline. The <i class="FIRSTTERM">height</i>
          of a font is the sum of the ascent and the descent. When
          rendering multiple lines of text, you should leave at
          least the font's height between each baseline.
        </p>
        <p>
          Ascent and descent are available as members of the <span
          class="STRUCTNAME">GdkFont</span> struct:
        </p>
        <table border="0" bgcolor="#E0E0E0" width="100%">
          <tr>
            <td>
<pre class="PROGRAMLISTING">
&#13;typedef struct _GdkFont GdkFont;

struct _GdkFont
{
  GdkFontType type;
  gint ascent;
  gint descent;
};&#13;
</pre>
            </td>
          </tr>
        </table>
        <p>
          The <span class="STRUCTNAME">type</span> field
          distinguishes fonts from fontsets; fontsets are used to
          display non-European languages.
        </p>
        <p>
          Individual characters in a font have their own ascent and
          descent; a character's ascent and descent will always be
          less than or equal to the font's ascent and descent. GDK
          can calculate the sum of the maximum ascent and descent
          for a particular string, rather than an entire font; this
          height will be less than or equal to the font's height.
          The relevant functions are <tt class="FUNCTION">
          gdk_string_height()</tt>, <tt class="FUNCTION">
          gdk_text_height()</tt>, and <tt class="FUNCTION">
          gdk_char_height()</tt>. <tt class="FUNCTION">
          gdk_text_height()</tt> is different from <tt class= 
          "FUNCTION">gdk_string_height()</tt> because it accepts
          the length of the string as an argument; <tt class= 
          "FUNCTION">gdk_string_height()</tt> calls <tt class= 
          "FUNCTION">strlen()</tt> for you. Thus <tt class=
          "FUNCTION">gdk_text_height()</tt> is preferred if you
          already know a string's length.
        </p>
        <p>
          In addition to its vertical metrics, each character in a
          font has three metrics describing its horizontal
          dimensions. The <i class="FIRSTTERM">width</i> of a
          character is the distance from the left origin of the
          character to the start of the next character. Note: the
          width is <i class="EMPHASIS">not</i> the distance to the
          furthest-right pixel in a character; in some fonts,
          especially italic fonts, characters may lean over past
          the start of the next character. The <i class=
          "FIRSTTERM">left-side-bearing</i> or <i class=
          "FIRSTTERM">lbearing</i> is the distance from the left
          origin to the leftmost pixel in the character; the <i
          class="FIRSTTERM">right-side-bearing</i> or <i class= 
          "FIRSTTERM">rbearing</i> is the distance from the origin
          to the rightmost pixel in the character. Thus the <i
          class="FIRSTTERM">rbearing</i> can be larger than the
          width, in the case of italic fonts that lean over past
          the start of the next character.
        </p>
        <p>
          GDK functions that return a character or string width
          return the width of the character, or the sum of the
          character widths in the string. If the rbearing of the
          rightmost character is greater than its width, a string
          may require more space than <tt class="FUNCTION">
          gdk_string_width()</tt>, <tt class="FUNCTION">
          gdk_text_width()</tt>, or <tt class="FUNCTION">
          gdk_char_width()</tt> will return. Like the
          height-measurement functions, the <span class=
          "STRUCTNAME">_string_</span> variant computes the length
          of the string for you, and the <span class="STRUCTNAME">
          _text_</span> variant accepts a precomputed length as an
          argument.
        </p>
        <p>
          The functions ending in <span class="STRUCTNAME">
          _measure</span> are more often what you want. For a
          string with <i class="EMPHASIS">N</i> characters, these
          return the sum of the widths of the first <i class= 
          "EMPHASIS">N-1</i> characters, plus the rbearing of the
          final character. That is, they take into account the fact
          that rbearing may be greater than width. If you're trying
          to decide how much space to leave for rendering a string,
          you probably want the <tt class="FUNCTION">
          gdk_string_measure()</tt>, <tt class="FUNCTION">
          gdk_text_measure()</tt>, or <tt class="FUNCTION">
          gdk_char_measure()</tt> functions. Sometimes you don't
          want to consider the rbearing, however; for example, if
          you're centering a string, it may look nicer to use the
          width (because a small italic flourish extending past the
          width won't "fill" the space and the string will look
          slightly left of center).
        </p>
        <p>
          <tt class="FUNCTION">gdk_text_extents()</tt> and <tt
          class="FUNCTION">gdk_string_extents()</tt> return <i
          class="EMPHASIS">all</i> the metrics for a string,
          including both bearings, the width, ascent, and descent.
          The returned left-side-bearing is the leftmost pixel in
          the string; the right-side-bearing is the rightmost pixel
          as returned by <tt class="FUNCTION">
          gdk_text_measure()</tt>. The width is the sum of
          character widths, as returned by <tt class="FUNCTION">
          gdk_text_width()</tt>.
        </p>
        <p>
          <a href="sec-gdkfont.html#FIG-FONTMETRICS">Figure 11</a>
          depicts the various font metrics. <a href= 
          "sec-gdkfont.html#FL-FONTMETRICS">Figure 12</a>
          summarizes the API for querying font metrics. All font
          metrics are computed on the client side, so these
          functions are not expensive compared to most of the
          drawing API.
        </p>
        <div class="FIGURE">
          <a name="FIG-FONTMETRICS"></a>
          <p>
            <img src="TO_BE_D.png">
          </p>
          <p>
            <b>Figure 11. Font Metrics</b>
          </p>
        </div>
        <div class="FIGURE">
          <a name="FL-FONTMETRICS"></a>
          <div class="FUNCSYNOPSIS">
            <a name="FL-FONTMETRICS.SYNOPSIS"></a>
            <table border="0" bgcolor="#E0E0E0" width="100%">
              <tr>
                <td>
<pre class="FUNCSYNOPSISINFO">
#include &lt;gdk/gdk.h&gt;
</pre>
                </td>
              </tr>
            </table>
            <p>
              <code><code class="FUNCDEF">gint <tt class=
              "FUNCTION">gdk_string_width</tt></code>(GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, const gchar* <tt
              class="PARAMETER"><i>string</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">gint <tt class=
              "FUNCTION">gdk_text_width</tt></code>(GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, const gchar* <tt
              class="PARAMETER"><i>string</i></tt>, gint <tt class= 
              "PARAMETER"><i>string_length</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">gint <tt class=
              "FUNCTION">gdk_char_width</tt></code>(GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, gchar <tt class= 
              "PARAMETER"><i>character</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">gint <tt class=
              "FUNCTION">gdk_string_measure</tt></code>(GdkFont*
              <tt class="PARAMETER"><i>font</i></tt>, const gchar*
              <tt class="PARAMETER"><i>string</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">gint <tt class=
              "FUNCTION">gdk_text_measure</tt></code>(GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, const gchar* <tt
              class="PARAMETER"><i>string</i></tt>, gint <tt class= 
              "PARAMETER"><i>string_length</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">gint <tt class=
              "FUNCTION">gdk_char_measure</tt></code>(GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, gchar <tt class= 
              "PARAMETER"><i>character</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">gint <tt class=
              "FUNCTION">gdk_string_height</tt></code>(GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, const gchar* <tt
              class="PARAMETER"><i>string</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">gint <tt class=
              "FUNCTION">gdk_text_height</tt></code>(GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, const gchar* <tt
              class="PARAMETER"><i>string</i></tt>, gint <tt class= 
              "PARAMETER"><i>string_length</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">gint <tt class=
              "FUNCTION">gdk_char_height</tt></code>(GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, gchar <tt class= 
              "PARAMETER"><i>character</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">void <tt class=
              "FUNCTION">gdk_string_extents</tt></code>(GdkFont*
              <tt class="PARAMETER"><i>font</i></tt>, const gchar*
              <tt class="PARAMETER"><i>string</i></tt>, gint* <tt
              class="PARAMETER"><i>lbearing</i></tt>, gint* <tt
              class="PARAMETER"><i>rbearing</i></tt>, gint* <tt
              class="PARAMETER"><i>width</i></tt>, gint* <tt class= 
              "PARAMETER"><i>ascent</i></tt>, gint* <tt class= 
              "PARAMETER"><i>descent</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">void <tt class=
              "FUNCTION">gdk_text_extents</tt></code>(GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, const gchar* <tt
              class="PARAMETER"><i>string</i></tt>, gint <tt class= 
              "PARAMETER"><i>string_length</i></tt>, gint* <tt
              class="PARAMETER"><i>lbearing</i></tt>, gint* <tt
              class="PARAMETER"><i>rbearing</i></tt>, gint* <tt
              class="PARAMETER"><i>width</i></tt>, gint* <tt class= 
              "PARAMETER"><i>ascent</i></tt>, gint* <tt class= 
              "PARAMETER"><i>descent</i></tt>);</code>
            </p>
          </div>
          <p>
            <b>Figure 12. Font Metrics</b>
          </p>
        </div>
      </div>
    </div>
    <div class="NAVFOOTER">
      <br>
      <br>
      <table width="100%" border="0" bgcolor="#ffffff" cellpadding= 
      "1" cellspacing="0">
        <tr>
          <td width="25%" bgcolor="#ffffff" align="left">
            <a href="sec-gdkcursor.html"><font color="#0000ff"
            size="2"><b>&lt;&lt;&lt; Previous</b></font></a>
          </td>
          <td width="25%" colspan="2" bgcolor="#ffffff" align= 
          "center">
            <font color="#0000ff" size="2"><b><a href="ggad.html">
            <font color="#0000ff" size="2"><b>
            Home</b></font></a></b></font>
          </td>
          <td width="25%" bgcolor="#ffffff" align="right">
            <a href="sec-gc.html"><font color="#0000ff" size="2">
            <b>Next &gt;&gt;&gt;</b></font></a>
          </td>
        </tr>
        <tr>
          <td colspan="2" align="left">
            <font color="#000000" size="2"><b>The Mouse
            Pointer</b></font>
          </td>
          <td colspan="2" align="right">
            <font color="#000000" size="2"><b>Graphics
            Contexts</b></font>
          </td>
        </tr>
      </table>
    </div>
  </body>
</html>