z132.html

GTK+_ Gnome Application Development

          or a portion of one. (<a href=
          "z132.html#FL-GDKARC">Figure 20</a>). The arc can be
          filled or unfilled; the third argument to the function
          toggles fill. The fourth through seventh arguments
          describe a rectangle; the ellipse is inscribed in this
          rectangle. <span class="STRUCTNAME">angle1</span> is the
          angle at which to start drawing; it is relative to the 3
          o'clock position (that is, 0 radians). <span class= 
          "STRUCTNAME">angle2</span> is the distance to travel
          around the arc; if positive, travel is counterclockwise,
          otherwise travel is clockwise. Both <span class= 
          "STRUCTNAME">angle1</span> and <span class="STRUCTNAME">
          angle2</span> are specified in sixty-fourths of a degree;
          so, 360 degrees is given as <span class="STRUCTNAME">
          360*64</span>. This allows more precise specification of
          the arc's size and shape, without using floating point
          numbers. <span class="STRUCTNAME">angle2</span> should
          not exceed 360 degrees, since it is nonsensical to move
          more than 360 degrees around the ellipse.
        </p>
        <p>
          To draw a circle, draw from 0 to 360*64 inside a square:
        </p>
        <table border="0" bgcolor="#E0E0E0" width="100%">
          <tr>
            <td>
<pre class="PROGRAMLISTING">
&#13;  gdk_draw_arc(drawable, gc, TRUE,
               0, 0, 
               50, 50,
               0, 360*64);&#13;
</pre>
            </td>
          </tr>
        </table>
        <p>
          To draw half an ellipse, change the aspect ratio and
          halve the span of the arc:
        </p>
        <table border="0" bgcolor="#E0E0E0" width="100%">
          <tr>
            <td>
<pre class="PROGRAMLISTING">
&#13;  gdk_draw_arc(drawable, gc, TRUE,
               0, 0, 
               100, 50, 
               0, 180*64);&#13;
</pre>
            </td>
          </tr>
        </table>
        <p>
          Many X servers draw the edges of filled arcs in an
          aesthetically unpleasing way; in particular, very small
          circles may not look very circular. You can work around
          this by also drawing the circle's outline.
        </p>
        <div class="FIGURE">
          <a name="FL-GDKARC"></a>
          <div class="FUNCSYNOPSIS">
            <a name="FL-GDKARC.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">void <tt class=
              "FUNCTION">gdk_draw_arc</tt></code>(GdkDrawable* <tt
              class="PARAMETER"><i>drawable</i></tt>, GdkGC* <tt
              class="PARAMETER"><i>gc</i></tt>, gint <tt class= 
              "PARAMETER"><i>filled</i></tt>, gint <tt class= 
              "PARAMETER"><i>x</i></tt>, gint <tt class=
              "PARAMETER"><i>y</i></tt>, gint <tt class=
              "PARAMETER"><i>width</i></tt>, gint <tt class= 
              "PARAMETER"><i>height</i></tt>, gint <tt class= 
              "PARAMETER"><i>angle1</i></tt>, gint <tt class= 
              "PARAMETER"><i>angle2</i></tt>);</code>
            </p>
          </div>
          <p>
            <b>Figure 20. Drawing Arcs</b>
          </p>
        </div>
      </div>
      <div class="SECT2">
        <h2 class="SECT2">
          <a name="Z137">Polygons</a>
        </h2>
        <p>
          <tt class="FUNCTION">gdk_draw_polygon()</tt> draws a
          filled or unfilled polygon (<a href=
          "z132.html#FL-GDKPOLY">Figure 21</a>). Notice that <tt
          class="FUNCTION">gdk_draw_lines()</tt> can also be used
          to draw an unfilled polygon (there is no reason to prefer
          one or the other). The arguments to <tt class="FUNCTION">
          gdk_draw_polygon()</tt> are the same as those to <tt
          class="FUNCTION">gdk_draw_lines()</tt>. The polygon does
          not have to be convex. It may also be self-intersecting.
          Self-intersecting polygons are filled with an "Even-Odd
          Rule," which means regions with an odd number of polygon
          areas overlapping them are not filled. That is, if the
          polygon does not overlap itself, it is entirely filled;
          if a region is overlapped once, it is not filled; if it's
          overlapped twice, it is filled; and so on.
        </p>
        <div class="FIGURE">
          <a name="FL-GDKPOLY"></a>
          <div class="FUNCSYNOPSIS">
            <a name="FL-GDKPOLY.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">void <tt class=
              "FUNCTION">gdk_draw_polygon</tt></code>(GdkDrawable*
              <tt class="PARAMETER"><i>drawable</i></tt>, GdkGC*
              <tt class="PARAMETER"><i>gc</i></tt>, gint <tt class= 
              "PARAMETER"><i>filled</i></tt>, GdkPoint* <tt class= 
              "PARAMETER"><i>points</i></tt>, gint <tt class= 
              "PARAMETER"><i>npoints</i></tt>);</code>
            </p>
          </div>
          <p>
            <b>Figure 21. Drawing Polygons</b>
          </p>
        </div>
      </div>
      <div class="SECT2">
        <h2 class="SECT2">
          <a name="Z138">Text</a>
        </h2>
        <p>
          There are two functions to draw strings; as an
          optimization, <tt class="FUNCTION">gdk_draw_text()</tt>
          takes the length of the string to draw as an argument.
          <tt class="FUNCTION">gdk_draw_string()</tt> uses <tt
          class="FUNCTION">strlen()</tt> to compute the string
          length for you. Otherwise the two are identical. The
          <span class="STRUCTNAME">x</span> and <span class= 
          "STRUCTNAME">y</span> coordinates specify the location of
          the left side of the text's baseline. See <a href= 
          "sec-gdkfont.html">the section called <i>Fonts</i></a>
          for more information on fonts and font metrics. Text is
          drawn in the foreground color.
        </p>
        <p>
          There is no way to draw scaled or rotated text with GDK.
          <span class="STRUCTNAME">GnomeCanvasText</span> offers a
          slow and low-quality way to render scaled and rotated
          text (see <a href= 
          "sec-itemreference.html#SEC-GNOMECANVASTEXT">the section
          called <i>Text Item</i> in the chapter called <i><tt
          class="CLASSNAME">GnomeCanvas</tt></i></a>). If you need
          high-quality scaling and rotating, you will need to use
          additional libraries, such as <tt class="APPLICATION">
          t1lib</tt> for Type 1 fonts or FreeType for True Type
          fonts. Another possibility is the Display Postscript
          extension to X (XDPS); the GNU Project is working on a
          free implementation of XDPS. The Gnome project also has a
          text solution in development, as part of the <tt class= 
          "APPLICATION">gnome-print</tt> library.
        </p>
        <div class="FIGURE">
          <a name="FL-GDKTEXT"></a>
          <div class="FUNCSYNOPSIS">
            <a name="FL-GDKTEXT.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">void <tt class=
              "FUNCTION">gdk_draw_string</tt></code>(GdkDrawable*
              <tt class="PARAMETER"><i>drawable</i></tt>, GdkFont*
              <tt class="PARAMETER"><i>font</i></tt>, GdkGC* <tt
              class="PARAMETER"><i>gc</i></tt>, gint <tt class= 
              "PARAMETER"><i>x</i></tt>, gint <tt class=
              "PARAMETER"><i>y</i></tt>, const gchar* <tt class= 
              "PARAMETER"><i>text</i></tt>);</code>
            </p>
            <p>
              <code><code class="FUNCDEF">void <tt class=
              "FUNCTION">gdk_draw_text</tt></code>(GdkDrawable* <tt
              class="PARAMETER"><i>drawable</i></tt>, GdkFont* <tt
              class="PARAMETER"><i>font</i></tt>, GdkGC* <tt class= 
              "PARAMETER"><i>gc</i></tt>, gint <tt class=
              "PARAMETER"><i>x</i></tt>, gint <tt class=
              "PARAMETER"><i>y</i></tt>, const gchar* <tt class= 
              "PARAMETER"><i>text</i></tt>, gint <tt class= 
              "PARAMETER"><i>text_length</i></tt>);</code>
            </p>
          </div>
          <p>
            <b>Figure 22. Drawing Text</b>
          </p>
        </div>
      </div>
      <div class="SECT2">
        <h2 class="SECT2">
          <a name="Z139">Pixmaps</a>
        </h2>
        <p>
          <tt class="FUNCTION">gdk_draw_pixmap()</tt> copies a
          region from a pixmap to another drawable (pixmap or
          window). The source and destination drawables must have
          the same depth and visual. If you pass <span class= 
          "STRUCTNAME">-1</span> for the width or height, the full
          size of the source pixmap is substituted. The source can
          actually be any drawable, including a window, but <tt
          class="FUNCTION">gdk_window_copy_area()</tt> will make
          your code clearer if the source is a window. <a href= 
          "z132.html#FL-GDKDRAWPIXMAP">Figure 23</a> shows <tt
          class="FUNCTION">gdk_draw_pixmap()</tt>.
        </p>
        <div class="FIGURE">
          <a name="FL-GDKDRAWPIXMAP"></a>
          <div class="FUNCSYNOPSIS">
            <a name="FL-GDKDRAWPIXMAP.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">void <tt class=
              "FUNCTION">gdk_draw_pixmap</tt></code>(GdkDrawable*
              <tt class="PARAMETER"><i>drawable</i></tt>, GdkGC*
              <tt class="PARAMETER"><i>gc</i></tt>, GdkDrawable*
              <tt class="PARAMETER"><i>src</i></tt>, gint <tt
              class="PARAMETER"><i>xsrc</i></tt>, gint <tt class= 
              "PARAMETER"><i>ysrc</i></tt>, gint <tt class= 
              "PARAMETER"><i>xdest</i></tt>, gint <tt class= 
              "PARAMETER"><i>ydest</i></tt>, gint <tt class= 
              "PARAMETER"><i>width</i></tt>, gint <tt class= 
              "PARAMETER"><i>height</i></tt>);</code>
            </p>
          </div>
          <p>
            <b>Figure 23. Drawing Pixmaps</b>