Gtk custom widget doesn't scroll

[giutor (Giuseppe)]

I made a custom widget by subclassing GtkLayout. From the documentation I read this widget has native scrolling abilities so it doesn’t need a Gtkviewport. The problem is my custom widget doesn’t scroll when I use the mouse wheel on it. I guess it’s an allocation problem but what shall I modify to have it to scroll? The widget extends itself up to 00:04:59.

#include <gtk/gtk.h>
#include “img_timeline.h”
#include <stdlib.h>

static gboolean img_timeline_scroll( ImgTimeline *widget, GdkEventScroll *event, GtkWidget *scrolledwindow);
static gboolean img_timeline_motion_notify(GtkWidget *widget, GdkEventMotion *event, gpointer data);

static gint zoom = 1;

int main(int argc, char *argv[])
{
gtk_init(&argc, &argv);

GtkWidget *window=gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_title(GTK_WINDOW(window), “Imagination timeline widget”);
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 800, 200);
g_signal_connect(window, “destroy”, G_CALLBACK(gtk_main_quit), NULL);

GtkWidget *timeline = img_timeline_new();
g_object_set(timeline, “total_time”, 300, NULL);
g_object_set(timeline, “video_background”, “#0084ff”, NULL);
g_object_set(timeline, “audio_background”, “#0084ff”, NULL);

gtk_widget_add_events( timeline, GDK_BUTTON1_MOTION_MASK
| GDK_POINTER_MOTION_MASK
| GDK_BUTTON_PRESS_MASK
| GDK_BUTTON_RELEASE_MASK
| GDK_SCROLL_MASK
| GDK_KEY_PRESS_MASK );

GtkWidget *scrolledwindow1 = gtk_scrolled_window_new(NULL,NULL);
gtk_scrolled_window_set_policy (GTK_SCROLLED_WINDOW (scrolledwindow1), GTK_POLICY_ALWAYS, GTK_POLICY_NEVER);
gtk_container_add (GTK_CONTAINER(scrolledwindow1), timeline);
gtk_container_add (GTK_CONTAINER (window), scrolledwindow1);
g_signal_connect( G_OBJECT(timeline), “scroll-event”, G_CALLBACK(img_timeline_scroll), scrolledwindow1);
g_signal_connect( G_OBJECT(timeline), “motion-notify-event”, G_CALLBACK( img_timeline_motion_notify ), NULL );
gtk_widget_show_all(window);

gtk_main();
return 0;
}

This is the widget.h:

#ifndef IMG_TIMELINE_H
#define IMG_TIMELINE_H

#include <gtk/gtk.h>

G_BEGIN_DECLS

struct _ImgTimeline
{
/< private >/
GtkLayout da;
};

enum
{
PROP_0,
//color properties
VIDEO_BACKGROUND,
AUDIO_BACKGROUND,
TOTAL_TIME,
TIME_MARKER_XPOS
};

#define IMG_TIMELINE_TYPE img_timeline_get_type()

G_DECLARE_FINAL_TYPE(ImgTimeline, img_timeline, IMG, TIMELINE, GtkLayout)

//Public functions.
GtkWidget* img_timeline_new();

//Set and get colors.
void img_timeline_set_video_background (ImgTimeline *da, const gchar *background_string);
void img_timeline_set_audio_background (ImgTimeline *da, const gchar *background_string);
void img_timeline_adjust_zoom (ImgTimeline *da, gint zoom, gint direction);
void img_timeline_set_total_time (ImgTimeline *da, gint total_time);
void img_timeline_add_slide (GtkWidget *da, cairo_t *cr, gchar *filename);
void img_timeline_draw_time_marker(GtkWidget *widget, cairo_t *cr, gint pos_X);
void img_timeline_set_time_marker(ImgTimeline *widget, gint pos_X);
void img_timeline_slide_clicked(GtkWidget *widget, gpointer data);
G_END_DECLS

#endif

This is the draw function:

static gboolean img_timeline_draw(GtkWidget *da, cairo_t *cr)
{
ImgTimelinePrivate priv = img_timeline_get_instance_private((ImgTimeline)da);

gint width = gtk_widget_get_allocated_width(da);

cairo_save(cr);
cairo_translate (cr, 0 , 12);
img_timeline_draw_time_ticks(da, cr, width);

//Video timeline
cairo_translate (cr, 0 , 20);
cairo_set_source_rgba(cr, priv->video_background[0], priv->video_background[1], priv->video_background[2], priv->video_background[3]);
cairo_set_line_width(cr, 1);
cairo_rectangle(cr, 0,10, width - 2, 54);
cairo_fill(cr);
//separator
cairo_set_source_rgb(cr, 1, 1, 1);
cairo_rectangle(cr, 0,64, width - 2, 3);
cairo_fill(cr);
//Audio timeline
cairo_set_source_rgba(cr, priv->audio_background[0], priv->audio_background[1], priv->audio_background[2], priv->audio_background[3]);
cairo_rectangle(cr, 0,68, width - 2, 54);
cairo_fill(cr);
cairo_restore(cr);

//This is necessary to draw the slides represented by the GtkButtons
GTK_WIDGET_CLASS (img_timeline_parent_class)->draw (da, cr);
return TRUE;
}

And this is the scroll function:

static gboolean img_timeline_scroll(ImgTimeline *timeline, GdkEventScroll *event, GtkWidget *scrolledwindow)
{
GdkModifierType accel_mask = gtk_accelerator_get_default_mod_mask();
GtkAdjustment *hadj = gtk_scrollable_get_hadjustment(GTK_SCROLLABLE(timeline));

if ( (event->state & accel_mask) == GDK_CONTROL_MASK)
{
g_print(“CTRL PRESSED\n”);
if (event->direction == GDK_SCROLL_UP)
{
g_print(“UP\n”);
zoom --;
}
else if (event->direction == GDK_SCROLL_DOWN)
{
g_print(“DOWN\n”);
zoom ++;
}
if (zoom < 1)
zoom = 1;
img_timeline_adjust_zoom(timeline, zoom, event->direction);
}
else if (event->direction == GDK_SCROLL_DOWN)
gtk_adjustment_set_value(hadj, gtk_adjustment_get_value(hadj) + 40);
else
gtk_adjustment_set_value(hadj, gtk_adjustment_get_value(hadj) - 40);

return TRUE;
}

Thank you so much in advance

[giutor (Giuseppe)]

If anyone wants to help here is the github project page: https://github.com/colossus73/gtk_timeline/

[fmuellner (Florian Müllner)]

@giutor

I made a custom widget by subclassing GtkLayout. From the documentation I read this widget has native scrolling abilities so it doesn’t need a Gtkviewport.

That is correct, but a bit misleading.

There are two parts of scrolling:

1. the ability of a widget to show a partial viewport, determined by horizontal and vertical adjustments
2. a widget to control scrolling, like adding scrollbars as necessary, and processing input events like mouse wheel scrolls to adjust the scroll position

GtkViewport is a generic implementation for 1., and some widget have native support for scrolling.

But you still need a second widget that does 2., usually GtkScrolledWindow.

[giutor (Giuseppe)]

Thank you so much indeed for replying. I added the viewport and I get now the scrollbars but the mouse wheel doesn’t scroll the custom widget.

static gboolean gtk_timeline_scroll(GtkWidget *timeline, GdkEventScroll *event, GtkWidget *scrolledwindow)
{
GdkModifierType accel_mask = gtk_accelerator_get_default_mod_mask();
GtkAdjustment *scrollX = gtk_scrollable_get_hadjustment(GTK_SCROLLABLE(timeline));
gdouble deltax, deltay;

//g_print(“scrollX: %2f\n”,gtk_adjustment_get_value(scrollX));
gdk_event_get_scroll_deltas((GdkEvent *)event, &deltax, &deltay);

if ( (event->state & accel_mask) == GDK_CONTROL_MASK)
{
if (deltay > 0)
zoom --;
else if (deltay < 0)
zoom ++;

if (zoom < 1)
    zoom = 1;
gtk_timeline_adjust_zoom(timeline, zoom, deltay);

}
else if (deltay > 0)
gtk_adjustment_set_value(scrollX, gtk_adjustment_get_value(scrollX) + 40);
else
gtk_adjustment_set_value(scrollX, gtk_adjustment_get_value(scrollX) - 40);

return TRUE;
}

Am I supposed to use gtk_adjustment_set_value() to move the scrollbars am I not?