<span class="STRUCTNAME">GDK_BUTTON_PRESS</span>&#13;            </p>          </li>          <li>            <p>              <span class="STRUCTNAME">              GDK_3BUTTON_PRESS</span>&#13;            </p>          </li>          <li>            <p>              <span class="STRUCTNAME">              GDK_BUTTON_RELEASE</span>&#13;            </p>          </li>        </ol>        <p>          The X server automatically causes a pointer grab when a          button is pressed, and releases it when it is released.          This means that the button release event always goes to          the same window that received the button press event.          Xlib allows you to change this behavior, but GDK does          not. (In the Xlib documentation, this automatic grab is          referred to as a "passive" grab. It's distinct from an          "active" grab initiated with <tt class="FUNCTION">          gdk_pointer_grab()</tt>, described in <a href=           "sec-gdkcursor.html#SEC-POINTERGRAB">the section called          <i>Grabbing the Pointer</i></a>.)        </p>        <p>          A button event is defined as follows:        </p>        <table border="0" bgcolor="#E0E0E0" width="100%">          <tr>            <td><pre class="PROGRAMLISTING">&#13;typedef struct _GdkEventButton GdkEventButton;struct _GdkEventButton{  GdkEventType type;  GdkWindow *window;  gint8 send_event;  guint32 time;  gdouble x;  gdouble y;  gdouble pressure;  gdouble xtilt;  gdouble ytilt;  guint state;  guint button;  GdkInputSource source;  guint32 deviceid;  gdouble x_root, y_root;};&#13;</pre>            </td>          </tr>        </table>        <p>          Button events are marked with a time stamp (<span class=           "STRUCTNAME">time</span>) by the X server. The time is          given in milliseconds of "server time"; every few weeks          the integer overflows and timestamps begin again at 0.          Thus, you should not rely on the value as an absolute          measure of time; it is intended only to determine          relative time between events.        </p>        <p>          The mouse pointer's X and Y coordinates (relative to the          window the event occurred in) are included in <span          class="STRUCTNAME">GdkEventButton</span>. Keep in mind          that the pointer may be outside the window (if a pointer          grab is in effect; see <a href="sec-gdkcursor.html">the          section called <i>The Mouse Pointer</i></a>). If the          pointer is outside the window, its coordinates could be          negative or larger than the window's size. Coordinates          are given as doubles rather than integers, because some          input devices such as graphics tablets have sub-pixel          resolution. For most purposes, you will want to cast the          doubles to integers. <span class="STRUCTNAME">          pressure</span>, <span class="STRUCTNAME">xtilt</span>,          and <span class="STRUCTNAME">ytilt</span> are also          special features of some input devices; they can be          ignored almost all the time.        </p>        <p>          The <span class="STRUCTNAME">state</span> member of <span          class="STRUCTNAME">GdkEventButton</span> indicates which          modifier keys or mouse buttons were held down an instant          before the button was pressed. It is a bitfield, with one          or more of the flags in <a href=           "sec-gdkevent.html#TAB-MODMASKS">Table 5</a> set. Since          the modifiers are read just before the button press, it          follows that button press events do not have the pressed          button in <span class="STRUCTNAME">state</span>, but          button release events do have it.        </p>        <p>          Be careful to check for the presence of certain bit          masks, rather than the exact value of <span class=           "STRUCTNAME">state</span>. That is, prefer this:        </p>        <table border="0" bgcolor="#E0E0E0" width="100%">          <tr>            <td><pre class="PROGRAMLISTING">&#13; if ( (state &amp; GDK_SHIFT_MASK) == GDK_SHIFT_MASK )&#13;</pre>            </td>          </tr>        </table>        <p>          and avoid this:        </p>        <table border="0" bgcolor="#E0E0E0" width="100%">          <tr>            <td><pre class="PROGRAMLISTING">&#13; if ( state == GDK_SHIFT_MASK )&#13;</pre>            </td>          </tr>        </table>        <p>          If you check the exact value of <span class="STRUCTNAME">          state</span>, your application will mysteriously stop          working if the user has Num Lock or some other obscure          modifier turned on.        </p>        <div class="TABLE">          <a name="TAB-MODMASKS"></a>          <p>            <b>Table 5. Modifier Masks for Key and Button            Events</b>          </p>          <table border="1" bgcolor="#E0E0E0" cellspacing="0"          cellpadding="4" class="CALSTABLE">            <tr>              <th align="LEFT" valign="TOP">                Modifier Mask              </th>              <th align="LEFT" valign="TOP">                Meaning              </th>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_SHIFT_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Shift              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_LOCK_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Caps Lock              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_CONTROL_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Control              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_MOD1_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Mod1 (often Meta or Alt)              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_MOD2_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Mod2              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_MOD3_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Mod3              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_MOD4_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Mod4              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_MOD5_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Mod5              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_BUTTON1_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Button 1              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_BUTTON2_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Button 2              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_BUTTON3_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Button 3              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_BUTTON4_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Button 4              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_BUTTON5_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Button 5              </td>            </tr>            <tr>              <td align="LEFT" valign="TOP">                <span class="STRUCTNAME">GDK_RELEASE_MASK</span>              </td>              <td align="LEFT" valign="TOP">                Key releases              </td>            </tr>          </table>        </div>        <p>          The <span class="STRUCTNAME">button</span> member of          <span class="STRUCTNAME">GdkEventButton</span> indicates          which button triggered the event (i.e., the button which          was pressed or released). Buttons are numbered from one          to five; most of the time, button one is the left button,          button two is the middle button, and button three is the          right button. Left-handed users might reverse these.          Button four and five events are generated by some scroll          wheel mice when you spin the scroll wheel; GTK+ attempts          to send capture these events and move nearby scroll bars.          You should probably ignore any events you receive for          buttons four or five.        </p>        <p>          The three standard mouse buttons have conventional          meanings in Gnome. Button one is used for selection, drag          and drop, and operating widgets: the most common tasks.          Button three typically activates a pop-up menu. Button          two is traditionally used to move objects, such as the          panel. Sometimes button one moves objects also; for          example, desktop icons can be moved with either button          one or two. It is a good idea to be consistent with other          applications whenever possible.        </p>        <p>          The <span class="STRUCTNAME">source</span> and <span          class="STRUCTNAME">deviceid</span> members are used to          determine which device triggered the event; the user may          have a graphics tablet and a mouse connected          simultaneously, for example. You can ignore these fields          unless you are writing an application that can take          advantage of non-mouse devices.        </p>        <p>          The last two members of <span class="STRUCTNAME">          GdkEventButton</span>, <span class="STRUCTNAME">          x_root</span> and <span class="STRUCTNAME">y_root</span>,          are the <span class="STRUCTNAME">x</span> and <span          class="STRUCTNAME">y</span> coordinates translated to be          relative to the root window rather than the window          receiving the event. You can use these as "absolute"          coordinates to compare events from two different windows.        </p>      </div>      <div class="SECT2">        <h2 class="SECT2">          <a name="Z120">Keyboard Events</a>        </h2>        <p>          There are only two types of key event: <span class=           "STRUCTNAME">GDK_KEY_PRESS</span> and <span class=           "STRUCTNAME">GDK_KEY_RELEASE</span>. Some hardware does          not generate key release events; you should not write          code that depends on <span class="STRUCTNAME">          GDK_KEY_RELEASE</span> events, though your code should          respond sanely if one is received.        </p>        <p>          Here are the contents of a key event:        </p>        <table border="0" bgcolor="#E0E0E0" width="100%">          <tr>            <td><pre class="PROGRAMLISTING">&#13;typedef struct _GdkEventKey GdkEventKey;struct _GdkEventKey{  GdkEventType type;  GdkWindow *window;  gint8 send_event;  guint32 time;  guint state;  guint keyval;  gint length;  gchar *string;};&#13;</pre>            </td>          </tr>        </table>        <p>          The first three members are the standard members from          <span class="STRUCTNAME">GdkEventAny</span>; the <span          class="STRUCTNAME">time</span> and <span class=          "STRUCTNAME">state</span> members are identical to those          found in <span class="STRUCTNAME">GdkEventButton</span>.        </p>        <p>          <span class="STRUCTNAME">keyval</span> contains a <i          class="FIRSTTERM">keysym</i>. The X server keeps a global          translation table which converts combinations of physical          keys and modifiers to keysyms. For example, the ke