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@ -2500,6 +2500,388 @@ gtk_misc_set_alignment(GTK_MISK(label), 1.0f, 1.0f);
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its parent, i.e. the object that you pack it into.</para>
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</sect2>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>How do I set the color and font of a GtkLabel using a
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Resource File?</title>
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<para>The widget name path constructed for a Label consists of
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the widget names of its object hierarchy as well, e.g.</para>
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<para><literallayout>
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<literal>window (name: humphrey)</literal>
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<literal> hbox</literal>
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<literal> label (name: mylabel)</literal>
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</literallayout></para>
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<para>The widget path your pattern needs to match would be:
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<literal>humphrey.GtkHBox.mylabel</literal></para>
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<para>The resource file may look something like:</para>
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<programlisting role="C">
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style "title"
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{
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fg[NORMAL] = {1.0, 0.0, 0.0}
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font = "-adobe-helvetica-bold-r-normal--*-140-*-*-*-*-*-*"
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}
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widget "*mylabel" style "title"
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</programlisting>
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<para>In your program, you would also need to give a name to
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the Label widget, which can be done using:</para>
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<programlisting role="C">
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label = gtk_label_new("Some Label Text");
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gtk_widget_set_name(label, "mylabel");
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gtk_widget_show(label);
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</programlisting>
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</sect2>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>How do I configure Tooltips in a Resource File?</title>
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<para>The tooltip's window is named "gtk-tooltips",
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GtkTooltips in itself is not a GtkWidget (though a GtkObject)
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and as such is not attempted to match any widget styles.</para>
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<para>So, you resource file should look something like:</para>
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<programlisting role="C">
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style "postie"
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{
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bg[NORMAL] = {1.0, 1.0, 0.0}
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}
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widget "gtk-tooltips*" style "postie"
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</programlisting>
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</sect2>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>I can't add more than (something like) 2000 chars in a
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GtkEntry. What's wrong?</title>
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<para>There is now a known problem in the GtkEntry widget. In
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the <literal>gtk_entry_insert_text()</literal> function, the
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following lines limit the number of chars in the entry to
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2047.</para>
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<programlisting role="C">
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/* The algorithms here will work as long as, the text size (a
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* multiple of 2), fits into a guint16 but we specify a shorter
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* maximum length so that if the user pastes a very long text, there
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* is not a long hang from the slow X_LOCALE functions. */
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if (entry->text_max_length == 0)
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max_length = 2047;
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else
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max_length = MIN (2047, entry->text_max_length);
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</programlisting>
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</sect2>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>How do I make a GtkEntry widget activate on pressing
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the Return key?</title>
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<para>The Entry widget emits an 'activate' signal when you
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press return in it. Just attach to the activate signal on the
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entry and do whatever you want to do. Typical code would
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be:</para>
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<programlisting role="C">
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entry = gtk_entry_new();
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gtk_signal_connect (GTK_OBJECT(entry), "activate",
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GTK_SIGNAL_FUNC(entry_callback),
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NULL);
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</programlisting>
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</sect2>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>How do I validate/limit/filter the input to a
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GtkEntry?</title>
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<para>If you want to validate the text that a user enters into
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a GtkEntry widget you can attach to the "insert_text" signal
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of the entry, and modify the text within the callback
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function. The example below forces all characters to
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uppercase, and limits the range of characters to A-Z. Note
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that the entry is cast to an object of type GtkEditable, from
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which GtkEntry is derived.</para>
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<programlisting role="C">
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#include <ctype.h>
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#include <gtk/gtk.h>
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void insert_text_handler (GtkEntry *entry,
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const gchar *text,
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gint length,
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gint *position,
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gpointer data)
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{
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GtkEditable *editable = GTK_EDITABLE(entry);
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int i, count=0;
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gchar *result = g_new (gchar, length);
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for (i=0; i < length; i++) {
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if (!isalpha(text[i]))
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continue;
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result[count++] = islower(text[i]) ? toupper(text[i]) : text[i];
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}
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if (count > 0) {
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gtk_signal_handler_block_by_func (GTK_OBJECT (editable),
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GTK_SIGNAL_FUNC (insert_text_handler),
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data);
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gtk_editable_insert_text (editable, result, count, position);
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gtk_signal_handler_unblock_by_func (GTK_OBJECT (editable),
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GTK_SIGNAL_FUNC (insert_text_handler),
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data);
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}
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gtk_signal_emit_stop_by_name (GTK_OBJECT (editable), "insert_text");
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g_free (result);
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}
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int main (int argc,
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char *argv[])
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{
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GtkWidget *window;
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GtkWidget *entry;
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gtk_init (&argc, &argv);
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/* create a new window */
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window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
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gtk_window_set_title(GTK_WINDOW (window), "GTK Entry");
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gtk_signal_connect(GTK_OBJECT (window), "delete_event",
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(GtkSignalFunc) gtk_exit, NULL);
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entry = gtk_entry_new();
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gtk_signal_connect(GTK_OBJECT(entry), "insert_text",
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GTK_SIGNAL_FUNC(insert_text_handler),
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NULL);
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gtk_container_add(GTK_CONTAINER (window), entry);
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gtk_widget_show(entry);
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gtk_widget_show(window);
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gtk_main();
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return(0);
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}
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</programlisting>
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</sect2>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>How do I use horizontal scrollbars with a GtkText
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widget?</title>
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<para>The short answer is that you can't. The current version
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of the GtkText widget does not support horizontal
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scrolling. There is an intention to completely rewrite the
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GtkText widget, at which time this limitation will be
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removed.</para>
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</sect2>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>How do I change the font of a GtkText widget?</title>
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<para>There are a couple of ways of doing this. As GTK+ allows
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the appearance of applications to be changed at run time using
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resources you can use something like the following in the
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appropriate file:</para>
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<programlisting role="C">
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style "text"
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{
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font = "-adobe-helvetica-medium-r-normal--*-100-*-*-*-*-*-*"
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}
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</programlisting>
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<para>Another way to do this is to load a font within your
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program, and then use this in the functions for adding text to
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the text widget. You can load a font using, for example:</para>
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<programlisting role="C">
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GdkFont *font;
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font = gdk_font_load("-adobe-helvetica-medium-r-normal--*-140-*-*-*-*-*-*");
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</programlisting>
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</sect2>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>How do I set the cursor position in a GtkText
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object?</title>
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<para>Notice that the response is valid for any object that
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inherits from the GtkEditable class.</para>
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<para>Are you sure that you want to move the cursor position?
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Most of the time, while the cursor position is good, the
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insertion point does not match the cursor position. If this
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apply to what you really want, then you should use the
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<literal>gtk_text_set_point()</literal> function. If you want
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to set the insertion point at the current cursor position, use
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the following:</para>
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<programlisting role="C">
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gtk_text_set_point(GTK_TEXT(text),
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gtk_editable_get_position(GTK_EDITABLE(text)));
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</programlisting>
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<para>If you want the insertion point to follow the cursor at
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all time, you should probably catch the button press event,
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and then move the insertion point. Be careful : you'll have to
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catch it after the widget has changed the cursor position
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though. Thomas Mailund Jensen proposed the following
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code:</para>
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<programlisting role="C">
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static void
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insert_bar (GtkWidget *text)
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{
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/* jump to cursor mark */
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gtk_text_set_point (GTK_TEXT (text),
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gtk_editable_get_position (GTK_EDITABLE (text)));
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gtk_text_insert (GTK_TEXT (text), NULL, NULL, NULL,
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"bar", strlen ("bar"));
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}
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int
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main (int argc, char *argv[])
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{
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GtkWidget *window, *text;
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gtk_init (&argc, &argv);
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window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
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text = gtk_text_new (NULL, NULL);
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gtk_text_set_editable (GTK_TEXT (text), TRUE);
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gtk_container_add (GTK_CONTAINER (window), text);
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/* connect after everything else */
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gtk_signal_connect_after (GTK_OBJECT(text), "button_press_event",
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GTK_SIGNAL_FUNC (insert_bar), NULL);
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gtk_widget_show_all(window);
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gtk_main();
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return 0;
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}
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</programlisting>
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<para>Now, if you really want to change the cursor position,
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you should use the
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<literal>gtk_editable_set_position()</literal>
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function.</para>
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</sect2>
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</sect1>
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</chapter>
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<!-- ***************************************************************** -->
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<chapter>
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<title>About GDK</title>
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<sect1>
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<title></title>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>What is GDK?</title>
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<para>GDK is basically a wrapper around the standard Xlib
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function calls. If you are at all familiar with Xlib, a lot of
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the functions in GDK will require little or no getting used
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to. All functions are written to provide an way to access Xlib
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functions in an easier and slightly more intuitive manner. In
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addition, since GDK uses GLib (see below), it will be more
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portable and safer to use on multiple platforms.</para>
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<!-- Examples, anybody? I've been mulling some over. NF -->
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</sect2>
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<!-- ----------------------------------------------------------------- -->
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<sect2>
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<title>How do I use color allocation?</title>
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<para>One of the nice things about GDK is that it's based on
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top of Xlib; this is also a problem, especially in the area of
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color management. If you want to use color in your program
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(drawing a rectangle or such, your code should look something
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like this:</para>
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<programlisting role="C">
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{
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GdkColor *color;
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int width, height;
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GtkWidget *widget;
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GdkGC *gc;
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...
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/* first, create a GC to draw on */
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gc = gdk_gc_new(widget->window);
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/* find proper dimensions for rectangle */
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gdk_window_get_size(widget->window, &width, &height);
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/* the color we want to use */
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color = (GdkColor *)malloc(sizeof(GdkColor));
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/* red, green, and blue are passed values, indicating the RGB triple
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* of the color we want to draw. Note that the values of the RGB components
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* within the GdkColor are taken from 0 to 65535, not 0 to 255.
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*/
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color->red = red * (65535/255);
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color->green = green * (65535/255);
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color->blue = blue * (65535/255);
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/* the pixel value indicates the index in the colormap of the color.
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* it is simply a combination of the RGB values we set earlier
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*/
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color->pixel = (gulong)(red*65536 + green*256 + blue);
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/* However, the pixel valule is only truly valid on 24-bit (TrueColor)
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* displays. Therefore, this call is required so that GDK and X can
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* give us the closest color available in the colormap
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*/
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gdk_color_alloc(gtk_widget_get_colormap(widget), color);
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/* set the foreground to our color */
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gdk_gc_set_foreground(gc, color);
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/* draw the rectangle */
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gdk_draw_rectangle(widget->window, gc, 1, 0, 0, width, height);
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...
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}
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</programlisting>
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</sect2>
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</sect1>
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</chapter>
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BST 2000 Tony Gale
Tony Gale