Ruler widgets are used to indicate the location of the mouse pointer in a given window. A window can have a vertical ruler spanning across the width and a horizontal ruler spanning down the height. A small triangular indicator on the ruler shows the exact location of the pointer relative to the ruler.
A ruler must first be created. Horizontal and vertical rulers are created using
GtkWidget *gtk_hruler_new( void ); /* horizontal ruler */ GtkWidget *gtk_vruler_new( void ); /* vertical ruler */ |
Once a ruler is created, we can define the unit of measurement. Units of measure for rulers can beGTK_PIXELS, GTK_INCHES or GTK_CENTIMETERS. This is set using
void gtk_ruler_set_metric( GtkRuler *ruler, GtkMetricType metric ); |
The default measure is GTK_PIXELS.
gtk_ruler_set_metric( GTK_RULER(ruler), GTK_PIXELS ); |
Other important characteristics of a ruler are how to mark the units of scale and where the position indicator is initially placed. These are set for a ruler using
void gtk_ruler_set_range( GtkRuler *ruler, gfloat lower, gfloat upper, gfloat position, gfloat max_size ); |
The lower and upper arguments define the extent of the ruler, and max_size is the largest possible number that will be displayed. Position defines the initial position of the pointer indicator within the ruler.
A vertical ruler can span an 800 pixel wide window thus
gtk_ruler_set_range( GTK_RULER(vruler), 0, 800, 0, 800); |
The markings displayed on the ruler will be from 0 to 800, with a number for every 100 pixels. If instead we wanted the ruler to range from 7 to 16, we would code
gtk_ruler_set_range( GTK_RULER(vruler), 7, 16, 0, 20); |
The indicator on the ruler is a small triangular mark that indicates the position of the pointer relative to the ruler. If the ruler is used to follow the mouse pointer, the motion_notify_event signal should be connected to the motion_notify_event method of the ruler. To follow all mouse movements within a window area, we would use
#define EVENT_METHOD(i, x) GTK_WIDGET_CLASS(GTK_OBJECT(i)->klass)->x gtk_signal_connect_object( GTK_OBJECT(area), "motion_notify_event", (GtkSignalFunc)EVENT_METHOD(ruler, motion_notify_event), GTK_OBJECT(ruler) ); |
The following example creates a drawing area with a horizontal ruler above it and a vertical ruler to the left of it. The size of the drawing area is 600 pixels wide by 400 pixels high. The horizontal ruler spans from 7 to 13 with a mark every 100 pixels, while the vertical ruler spans from 0 to 400 with a mark every 100 pixels. Placement of the drawing area and the rulers is done using a table.
/* example-start rulers rulers.c */ #include <gtk/gtk.h> #define EVENT_METHOD(i, x) GTK_WIDGET_CLASS(GTK_OBJECT(i)->klass)->x #define XSIZE 600 #define YSIZE 400 /* This routine gets control when the close button is clicked */ gint close_application( GtkWidget *widget, GdkEvent *event, gpointer data ) { gtk_main_quit(); return(FALSE); } /* The main routine */ int main( int argc, char *argv[] ) { GtkWidget *window, *table, *area, *hrule, *vrule; /* Initialize GTK and create the main window */ gtk_init( &argc, &argv ); window = gtk_window_new( GTK_WINDOW_TOPLEVEL ); gtk_signal_connect (GTK_OBJECT (window), "delete_event", GTK_SIGNAL_FUNC( close_application ), NULL); gtk_container_set_border_width (GTK_CONTAINER (window), 10); /* Create a table for placing the ruler and the drawing area */ table = gtk_table_new( 3, 2, FALSE ); gtk_container_add( GTK_CONTAINER(window), table ); area = gtk_drawing_area_new(); gtk_drawing_area_size( (GtkDrawingArea *)area, XSIZE, YSIZE ); gtk_table_attach( GTK_TABLE(table), area, 1, 2, 1, 2, GTK_EXPAND|GTK_FILL, GTK_FILL, 0, 0 ); gtk_widget_set_events( area, GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK ); /* The horizontal ruler goes on top. As the mouse moves across the * drawing area, a motion_notify_event is passed to the * appropriate event handler for the ruler. */ hrule = gtk_hruler_new(); gtk_ruler_set_metric( GTK_RULER(hrule), GTK_PIXELS ); gtk_ruler_set_range( GTK_RULER(hrule), 7, 13, 0, 20 ); gtk_signal_connect_object( GTK_OBJECT(area), "motion_notify_event", (GtkSignalFunc)EVENT_METHOD(hrule, motion_notify_event), GTK_OBJECT(hrule) ); /* GTK_WIDGET_CLASS(GTK_OBJECT(hrule)->klass)->motion_notify_event, */ gtk_table_attach( GTK_TABLE(table), hrule, 1, 2, 0, 1, GTK_EXPAND|GTK_SHRINK|GTK_FILL, GTK_FILL, 0, 0 ); /* The vertical ruler goes on the left. As the mouse moves across * the drawing area, a motion_notify_event is passed to the * appropriate event handler for the ruler. */ vrule = gtk_vruler_new(); gtk_ruler_set_metric( GTK_RULER(vrule), GTK_PIXELS ); gtk_ruler_set_range( GTK_RULER(vrule), 0, YSIZE, 10, YSIZE ); gtk_signal_connect_object( GTK_OBJECT(area), "motion_notify_event", (GtkSignalFunc) GTK_WIDGET_CLASS(GTK_OBJECT(vrule)->klass)-> motion_notify_event, GTK_OBJECT(vrule) ); gtk_table_attach( GTK_TABLE(table), vrule, 0, 1, 1, 2, GTK_FILL, GTK_EXPAND|GTK_SHRINK|GTK_FILL, 0, 0 ); /* Now show everything */ gtk_widget_show( area ); gtk_widget_show( hrule ); gtk_widget_show( vrule ); gtk_widget_show( table ); gtk_widget_show( window ); gtk_main(); return(0); } /* example-end */ |