gtk_tut-20.html

gtk 开发手册和参考文档。 包括gtk glib gdk等

  attributes.event_mask = gtk_widget_get_events (widget) | 
    GDK_EXPOSURE_MASK | GDK_BUTTON_PRESS_MASK | 
    GDK_BUTTON_RELEASE_MASK | GDK_POINTER_MOTION_MASK |
    GDK_POINTER_MOTION_HINT_MASK;
  attributes.visual = gtk_widget_get_visual (widget);
  attributes.colormap = gtk_widget_get_colormap (widget);

  attributes_mask = GDK_WA_X | GDK_WA_Y | GDK_WA_VISUAL | GDK_WA_COLORMAP;
  widget->window = gdk_window_new (widget->parent->window, &attributes, attributes_mask);

  widget->style = gtk_style_attach (widget->style, widget->window);

  gdk_window_set_user_data (widget->window, widget);

  gtk_style_set_background (widget->style, widget->window, GTK_STATE_ACTIVE);
}
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H3>大小的设定</H3>

<P>
在所有视窗被显示出来之前, GTK会先问每个子物件的大小.

该事件是由<CODE>gtk_dial_size_request()</CODE>所处理的. 

既然我们的物件不是container物件, 而且没什麽大小约束,
就用个合理的数字就行了.
<P>
<BLOCKQUOTE><CODE>
<PRE>
static void 
gtk_dial_size_request (GtkWidget      *widget,
                       GtkRequisition *requisition)
{
  requisition-&gt;width = DIAL_DEFAULT_SIZE;
  requisition-&gt;height = DIAL_DEFAULT_SIZE;
}
</PRE>
</CODE></BLOCKQUOTE>
<P>
<P>
最後所有物件都有理想的大小.
一般会尽可能用原定大小,
但使用者会改变它的大小.
大小的改变是由<CODE>gtk_dial_size_allocate()</CODE>. 
<P>
<BLOCKQUOTE><CODE>
<PRE>
static void
gtk_dial_size_allocate (GtkWidget     *widget,
                        GtkAllocation *allocation)
{
  GtkDial *dial;

  g_return_if_fail (widget != NULL);
  g_return_if_fail (GTK_IS_DIAL (widget));
  g_return_if_fail (allocation != NULL);

  widget-&gt;allocation = *allocation;
  if (GTK_WIDGET_REALIZED (widget))
    {
      dial = GTK_DIAL (widget);

      gdk_window_move_resize (widget-&gt;window,
                              allocation-&gt;x, allocation-&gt;y,
                              allocation-&gt;width, allocation-&gt;height);

      dial-&gt;radius = MAX(allocation-&gt;width,allocation-&gt;height) * 0.45;
      dial-&gt;pointer_width = dial-&gt;radius / 5;
    }
}
</PRE>
</CODE></BLOCKQUOTE>
.
<P>
<H3><CODE>gtk_dial_expose()</CODE></H3>

<P>
就如之前所提到的一样,
所有物件的绘出都是由expose事件来处理.
没什麽可多提的, 除了用<CODE>gtk_draw_polygon</CODE> 
来画出三维阴影.
<P>
<BLOCKQUOTE><CODE>
<PRE>
static gint
gtk_dial_expose (GtkWidget      *widget,
                 GdkEventExpose *event)
{
  GtkDial *dial;
  GdkPoint points[3];
  gdouble s,c;
  gdouble theta;
  gint xc, yc;
  gint tick_length;
  gint i;

  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  if (event-&gt;count &gt; 0)
    return FALSE;
  
  dial = GTK_DIAL (widget);

  gdk_window_clear_area (widget-&gt;window,
                         0, 0,
                         widget-&gt;allocation.width,
                         widget-&gt;allocation.height);

  xc = widget-&gt;allocation.width/2;
  yc = widget-&gt;allocation.height/2;

  /* Draw ticks */

  for (i=0; i&lt;25; i++)
    {
      theta = (i*M_PI/18. - M_PI/6.);
      s = sin(theta);
      c = cos(theta);

      tick_length = (i%6 == 0) ? dial-&gt;pointer_width : dial-&gt;pointer_width/2;
      
      gdk_draw_line (widget-&gt;window,
                     widget-&gt;style-&gt;fg_gc[widget-&gt;state],
                     xc + c*(dial-&gt;radius - tick_length),
                     yc - s*(dial-&gt;radius - tick_length),
                     xc + c*dial-&gt;radius,
                     yc - s*dial-&gt;radius);
    }

  /* Draw pointer */

  s = sin(dial-&gt;angle);
  c = cos(dial-&gt;angle);


  points[0].x = xc + s*dial-&gt;pointer_width/2;
  points[0].y = yc + c*dial-&gt;pointer_width/2;
  points[1].x = xc + c*dial-&gt;radius;
  points[1].y = yc - s*dial-&gt;radius;
  points[2].x = xc - s*dial-&gt;pointer_width/2;
  points[2].y = yc - c*dial-&gt;pointer_width/2;

  gtk_draw_polygon (widget-&gt;style,
                    widget-&gt;window,
                    GTK_STATE_NORMAL,
                    GTK_SHADOW_OUT,
                    points, 3,
                    TRUE);
  
  return FALSE;
}
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H3>事件处理</H3>

<P>
<P>
最後一段程式处理各种事件,
跟我们之前所做的没有什麽太大的不同.
有两种事件会发生, 使用者滑鼠的动作及其它因素所造成的物件参数调整.
 
<P>
<P>
当使用者在物件上按钮时, 我们检查是否靠近我们的指标,
如果是, 将资料存到<CODE>button</CODE>一栏,
并用<CODE>gtk_grab_add()</CODE>将所有滑鼠事件抓住. 
接下来的滑鼠的动作将会被<CODE>gtk_dial_update_mouse</CODE>所接管.. 
接下来就看我们是如何做的,
"value_changed"事件可以用(<CODE>GTK_UPDATE_CONTINUOUS</CODE>)来产生, 
或用<CODE>gtk_timeout_add()</CODE>来延迟一下(<CODE>GTK_UPDATE_DELAYED</CODE>), 
或仅在按钮按下时反应(<CODE>GTK_UPDATE_DISCONTINUOUS</CODE>).
<P>
<BLOCKQUOTE><CODE>
<PRE>
static gint
gtk_dial_button_press (GtkWidget      *widget,
                       GdkEventButton *event)
{
  GtkDial *dial;
  gint dx, dy;
  double s, c;
  double d_parallel;
  double d_perpendicular;

  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  dial = GTK_DIAL (widget);

  /* Determine if button press was within pointer region - we 
     do this by computing the parallel and perpendicular distance of
     the point where the mouse was pressed from the line passing through
     the pointer */
  
  dx = event-&gt;x - widget-&gt;allocation.width / 2;
  dy = widget-&gt;allocation.height / 2 - event-&gt;y;
  
  s = sin(dial-&gt;angle);
  c = cos(dial-&gt;angle);
  
  d_parallel = s*dy + c*dx;
  d_perpendicular = fabs(s*dx - c*dy);
  
  if (!dial-&gt;button &&
      (d_perpendicular &lt; dial-&gt;pointer_width/2) &&
      (d_parallel &gt; - dial-&gt;pointer_width))
    {
      gtk_grab_add (widget);

      dial-&gt;button = event-&gt;button;

      gtk_dial_update_mouse (dial, event-&gt;x, event-&gt;y);
    }

  return FALSE;
}

static gint
gtk_dial_button_release (GtkWidget      *widget,
                          GdkEventButton *event)
{
  GtkDial *dial;

  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  dial = GTK_DIAL (widget);

  if (dial-&gt;button == event-&gt;button)
    {
      gtk_grab_remove (widget);

      dial-&gt;button = 0;

      if (dial-&gt;policy == GTK_UPDATE_DELAYED)
        gtk_timeout_remove (dial-&gt;timer);
      
      if ((dial-&gt;policy != GTK_UPDATE_CONTINUOUS) &&
          (dial-&gt;old_value != dial-&gt;adjustment-&gt;value))
        gtk_signal_emit_by_name (GTK_OBJECT (dial-&gt;adjustment), &quot;value_changed&quot;);
    }

  return FALSE;
}

static gint
gtk_dial_motion_notify (GtkWidget      *widget,
                         GdkEventMotion *event)
{
  GtkDial *dial;
  GdkModifierType mods;
  gint x, y, mask;

  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  dial = GTK_DIAL (widget);

  if (dial-&gt;button != 0)
    {
      x = event-&gt;x;
      y = event-&gt;y;

      if (event-&gt;is_hint || (event-&gt;window != widget-&gt;window))
        gdk_window_get_pointer (widget-&gt;window, &amp;x, &amp;y, &amp;mods);

      switch (dial-&gt;button)
        {
        case 1:
          mask = GDK_BUTTON1_MASK;
          break;
        case 2:
          mask = GDK_BUTTON2_MASK;
          break;
        case 3:
          mask = GDK_BUTTON3_MASK;
          break;
        default:
          mask = 0;
          break;
        }

      if (mods & mask)
        gtk_dial_update_mouse (dial, x,y);
    }

  return FALSE;
}

static gint
gtk_dial_timer (GtkDial *dial)
{
  g_return_val_if_fail (dial != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (dial), FALSE);

  if (dial-&gt;policy == GTK_UPDATE_DELAYED)
    gtk_signal_emit_by_name (GTK_OBJECT (dial-&gt;adjustment), &quot;value_changed&quot;);

  return FALSE;
}

static void
gtk_dial_update_mouse (GtkDial *dial, gint x, gint y)
{
  gint xc, yc;
  gfloat old_value;

  g_return_if_fail (dial != NULL);
  g_return_if_fail (GTK_IS_DIAL (dial));

  xc = GTK_WIDGET(dial)-&gt;allocation.width / 2;
  yc = GTK_WIDGET(dial)-&gt;allocation.height / 2;

  old_value = dial-&gt;adjustment-&gt;value;
  dial-&gt;angle = atan2(yc-y, x-xc);

  if (dial-&gt;angle &lt; -M_PI/2.)
    dial-&gt;angle += 2*M_PI;

  if (dial-&gt;angle &lt; -M_PI/6)
    dial-&gt;angle = -M_PI/6;

  if (dial-&gt;angle &gt; 7.*M_PI/6.)
    dial-&gt;angle = 7.*M_PI/6.;

  dial-&gt;adjustment-&gt;value = dial-&gt;adjustment-&gt;lower + (7.*M_PI/6 - dial-&gt;angle) *
    (dial-&gt;adjustment-&gt;upper - dial-&gt;adjustment-&gt;lower) / (4.*M_PI/3.);

  if (dial-&gt;adjustment-&gt;value != old_value)
    {
      if (dial-&gt;policy == GTK_UPDATE_CONTINUOUS)
        {
          gtk_signal_emit_by_name (GTK_OBJECT (dial-&gt;adjustment), &quot;value_changed&quot;);
        }
      else
        {
          gtk_widget_draw (GTK_WIDGET(dial), NULL);

          if (dial-&gt;policy == GTK_UPDATE_DELAYED)
            {
              if (dial-&gt;timer)
                gtk_timeout_remove (dial-&gt;timer);

              dial-&gt;timer = gtk_timeout_add (SCROLL_DELAY_LENGTH,
                                             (GtkFunction) gtk_dial_timer,
                                             (gpointer) dial);
            }
        }
    }
}

static void
gtk_dial_update (GtkDial *dial)
{
  gfloat new_value;
  
  g_return_if_fail (dial != NULL);
  g_return_if_fail (GTK_IS_DIAL (dial));

  new_value = dial-&gt;adjustment-&gt;value;
  
  if (new_value &lt; dial-&gt;adjustment-&gt;lower)
    new_value = dial-&gt;adjustment-&gt;lower;

  if (new_value &gt; dial-&gt;adjustment-&gt;upper)
    new_value = dial-&gt;adjustment-&gt;upper;

  if (new_value != dial-&gt;adjustment-&gt;value)
    {
      dial-&gt;adjustment-&gt;value = new_value;
      gtk_signal_emit_by_name (GTK_OBJECT (dial-&gt;adjustment), &quot;value_changed&quot;);
    }

  dial-&gt;angle = 7.*M_PI/6. - (new_value - dial-&gt;adjustment-&gt;lower) * 4.*M_PI/3. /
    (dial-&gt;adjustment-&gt;upper - dial-&gt;adjustment-&gt;lower);

  gtk_widget_draw (GTK_WIDGET(dial), NULL);
}

static void
gtk_dial_adjustment_changed (GtkAdjustment *adjustment,
                              gpointer       data)
{
  GtkDial *dial;

  g_return_if_fail (adjustment != NULL);
  g_return_if_fail (data != NULL);

  dial = GTK_DIAL (data);

  if ((dial-&gt;old_value != adjustment-&gt;value) ||
      (dial-&gt;old_lower != adjustment-&gt;lower) ||
      (dial-&gt;old_upper != adjustment-&gt;upper))
    {
      gtk_dial_update (dial);

      dial-&gt;old_value = adjustment-&gt;value;
      dial-&gt;old_lower = adjustment-&gt;lower;
      dial-&gt;old_upper = adjustment-&gt;upper;
    }
}

static void
gtk_dial_adjustment_value_changed (GtkAdjustment *adjustment,
                                    gpointer       data)
{
  GtkDial *dial;

  g_return_if_fail (adjustment != NULL);
  g_return_if_fail (data != NULL);

  dial = GTK_DIAL (data);

  if (dial-&gt;old_value != adjustment-&gt;value)
    {
      gtk_dial_update (dial);

      dial-&gt;old_value = adjustment-&gt;value;
    }
}
</PRE>
</CODE></BLOCKQUOTE>
<P>
<H3>有可能的增强之处</H3>

<P>
<P>
这个Dial物件到目前为止有670行.

这看起来好像有不少了,
不过我们真正完成的只有一点点,
因为大部份都是标头及模子.
还是有许多可以加强的地方:

<P>
<UL>
<LI> 
如果您试过这个物件,
您会发现滑鼠指标会一闪一闪的.
这是因为整个物件每次都重画一次.
当然了最好的方式是在offscreen pixmap上画完以後,
然後整个复制到萤幕上.

</LI>
<LI> 
使用者应该可以用up及down按键来增加或减少其值.
</LI>
<LI> 
如果有个按钮来增加或减少其值, 那是再好不过的了.

虽然可也以用embedded Button widgets来做,
但我们会想要按钮有auto-repeat的功能.
所有要做这一类功能的程式可以在GtkRange物件中发现.
</LI>
<LI> 
这个Dial物件可再做进一个container物件, 带有一个子物件, 位於按钮与最下面之间.
使用者可以增加一个标签或整个物件来显示目前的值.

</LI>
</UL>
<P>
<H2><A NAME="ss20.5">20.5 更多一点</A>
</H2>

<P>
关於产生一个新的物件的细部资讯在以上被提供出来.
如果您想要写一个属於自己的物件, 我想最好的范例就是GTK本身了.
<P>
问问您自己一些关於您想要写的物件:
<PRE>
它是否是个Container物件?
它是否有自己的视窗?
是否是个现有物件的修改?
找出一个相近的物件, 然後开始动工.
</PRE>
祝好运!
<P>
<H2><A NAME="ss20.6">20.6 版权</A>
</H2>

<P>This section on of the tutorial on writing widgets is 
Copyright (C) 1997 Owen Taylor
<P>This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
<P>This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
<P>You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
<P>
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