How catch mouse wheel up/down events using GTK3? - c

Question

how do I implement mouse wheel up/down events using C GTK3?
I have adapted this code in order to handle mouse scoll events:
#include <cairo.h>
#include <gtk/gtk.h>
static void do_drawing(cairo_t *);
struct {
int count;
double coordx[100];
double coordy[100];
} glob;
static gboolean on_draw_event(GtkWidget *widget, cairo_t *cr,
gpointer user_data)
{
do_drawing(cr);
return FALSE;
}
static void do_drawing(cairo_t *cr)
{
cairo_set_source_rgb(cr, 0, 0, 0);
cairo_set_line_width(cr, 0.5);
int i, j;
for (i = 0; i <= glob.count - 1; i++ ) {
for (j = 0; j <= glob.count - 1; j++ ) {
cairo_move_to(cr, glob.coordx[i], glob.coordy[i]);
cairo_line_to(cr, glob.coordx[j], glob.coordy[j]);
}
}
glob.count = 0;
cairo_stroke(cr);
}
static gboolean clicked(GtkWidget *widget, GdkEventButton *event,
gpointer user_data)
{
if (event->button == 1) {
glob.coordx[glob.count] = event->x;
glob.coordy[glob.count++] = event->y;
}
if (event->button == 3) {
gtk_widget_queue_draw(widget);
}
return TRUE;
}
static gboolean mouse_scroll (GtkWidget *widget,
GdkEvent *event,
gpointer user_data)
{
printf("scrolled up! \n");
return TRUE;
}
int main(int argc, char *argv[])
{
GtkWidget *window;
GtkWidget *darea;
glob.count = 0;
gtk_init(&argc, &argv);
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
darea = gtk_drawing_area_new();
gtk_container_add(GTK_CONTAINER(window), darea);
gtk_widget_add_events(window, GDK_BUTTON_PRESS_MASK);
gtk_widget_add_events(window, GDK_SCROLL_MASK);
g_signal_connect(G_OBJECT(darea), "draw",
G_CALLBACK(on_draw_event), NULL);
g_signal_connect(window, "destroy",
G_CALLBACK(gtk_main_quit), NULL);
g_signal_connect(window, "button-press-event",
G_CALLBACK(clicked), NULL);
g_signal_connect(window, "scroll-event",
G_CALLBACK(mouse_scroll), NULL);
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 400, 300);
gtk_window_set_title(GTK_WINDOW(window), "Lines");
gtk_widget_show_all(window);
gtk_main();
return 0;
}
However, this only catches a general mouse event, irrespective of whether the mouse is scrolled up or down. I want to know how can I get it to printf("scrolled up! \n") only when the mouse wheel is scrolled up.
Any ideas?

Answer 1

The *event parameter in mouse_scroll should point to GdkEventScroll structure which has direction member:
GdkScrollDirection direction; the direction to scroll to (one of
GDK_SCROLL_UP, GDK_SCROLL_DOWN, GDK_SCROLL_LEFT,
GDK_SCROLL_RIGHT or GDK_SCROLL_SMOOTH).