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Up: Readme.md, Prev: Section 22, Next: Section 24
Periodic Events
This chapter was written by Paul Schulz paul@mawsonlakes.org.
How do we create an animation?
In this section we will continue to build on our previous work. We will create an analog clock application. By adding a function which periodically redraws GtkDrawingArea, the clock will be able to continuously display the time.
The application uses a compiled in 'resource' file, so if the GTK4 libraries and their dependencies are installed and available, the application will run from anywhere.
The program also makes use of some standard mathematical and time handling functions.
The clocks mechanics were taken from a Cairo drawing example, using gtkmm4, which can be found here.
The complete code is at the end.
Drawing the clock face, hour, minute and second hands
The draw_clock() function does all the work. See the in-file comments for an
explanation of how the Cairo drawing works.
For a detailed reference of what each of the Cairo functions does see the cairo_t reference.
1 static void
2 draw_clock (GtkDrawingArea *area, cairo_t *cr, int width, int height, gpointer user_data) {
3
4 // Scale to unit square and translate (0, 0) to be (0.5, 0.5), i.e.
5 // the center of the window
6 cairo_scale(cr, width, height);
7 cairo_translate(cr, 0.5, 0.5);
8
9 // Set the line width and save the cairo drawing state.
10 cairo_set_line_width(cr, m_line_width);
11 cairo_save(cr);
12
13 // Set the background to a slightly transparent green.
14 cairo_set_source_rgba(cr, 0.337, 0.612, 0.117, 0.9); // green
15 cairo_paint(cr);
16
17 // Resore back to precious drawing state and draw the circular path
18 // representing the clockface. Save this state (including the path) so we
19 // can reuse it.
20 cairo_restore(cr);
21 cairo_arc(cr, 0.0, 0.0, m_radius, 0.0, 2.0 * M_PI);
22 cairo_save(cr);
23
24 // Fill the clockface with white
25 cairo_set_source_rgba(cr, 1.0, 1.0, 1.0, 0.8);
26 cairo_fill_preserve(cr);
27 // Restore the path, paint the outside of the clock face.
28 cairo_restore(cr);
29 cairo_stroke_preserve(cr);
30 // Set the 'clip region' to the inside of the path (fill region).
31 cairo_clip(cr);
32
33 // Clock ticks
34 for (int i = 0; i < 12; i++)
35 {
36 // Major tick size
37 double inset = 0.05;
38
39 // Save the graphics state, restore after drawing tick to maintain pen
40 // size
41 cairo_save(cr);
42 cairo_set_line_cap(cr, CAIRO_LINE_CAP_ROUND);
43
44 // Minor ticks are shorter, and narrower.
45 if(i % 3 != 0)
46 {
47 inset *= 0.8;
48 cairo_set_line_width(cr, 0.03);
49 }
50
51 // Draw tick mark
52 cairo_move_to(
53 cr,
54 (m_radius - inset) * cos (i * M_PI / 6.0),
55 (m_radius - inset) * sin (i * M_PI / 6.0));
56 cairo_line_to(
57 cr,
58 m_radius * cos (i * M_PI / 6.0),
59 m_radius * sin (i * M_PI / 6.0));
60 cairo_stroke(cr);
61 cairo_restore(cr); /* stack-pen-size */
62 }
63
64 // Draw the analog hands
65
66 // Get the current Unix time, convert to the local time and break into time
67 // structure to read various time parts.
68 time_t rawtime;
69 time(&rawtime);
70 struct tm * timeinfo = localtime (&rawtime);
71
72 // Calculate the angles of the hands of our clock
73 double hours = timeinfo->tm_hour * M_PI / 6.0;
74 double minutes = timeinfo->tm_min * M_PI / 30.0;
75 double seconds = timeinfo->tm_sec * M_PI / 30.0;
76
77 // Save the graphics state
78 cairo_save(cr);
79 cairo_set_line_cap(cr, CAIRO_LINE_CAP_ROUND);
80
81 cairo_save(cr);
82
83 // Draw the seconds hand
84 cairo_set_line_width(cr, m_line_width / 3.0);
85 cairo_set_source_rgba(cr, 0.7, 0.7, 0.7, 0.8); // gray
86 cairo_move_to(cr, 0.0, 0.0);
87 cairo_line_to(cr,
88 sin(seconds) * (m_radius * 0.9),
89 -cos(seconds) * (m_radius * 0.9));
90 cairo_stroke(cr);
91 cairo_restore(cr);
92
93 // Draw the minutes hand
94 cairo_set_source_rgba(cr, 0.117, 0.337, 0.612, 0.9); // blue
95 cairo_move_to(cr, 0, 0);
96 cairo_line_to(cr,
97 sin(minutes + seconds / 60) * (m_radius * 0.8),
98 -cos(minutes + seconds / 60) * (m_radius * 0.8));
99 cairo_stroke(cr);
100
101 // draw the hours hand
102 cairo_set_source_rgba(cr, 0.337, 0.612, 0.117, 0.9); // green
103 cairo_move_to(cr, 0.0, 0.0);
104 cairo_line_to(cr,
105 sin(hours + minutes / 12.0) * (m_radius * 0.5),
106 -cos(hours + minutes / 12.0) * (m_radius * 0.5));
107 cairo_stroke(cr);
108 cairo_restore(cr);
109
110 // Draw a little dot in the middle
111 cairo_arc(cr, 0.0, 0.0, m_line_width / 3.0, 0.0, 2.0 * M_PI);
112 cairo_fill(cr);
113 }
In order for the clock to be drawn, the drawing function draw_clock() needs
to be registered with GTK4. This is done in the app_activate() function (on line 24).
Whenever the application needs to redraw the GtkDrawingArea, it will now call draw_clock().
There is still a problem though. In order to animate the clock we need to also
tell the application that the clock needs to be redrawn every second. This
process starts by registering (on the next line, line 15) a timeout function
with g_timeout_add() that will wakeup and run another function time_handler,
every second (or 1000ms).
1 static void
2 app_activate (GApplication *app, gpointer user_data) {
3 GtkWidget *win;
4 GtkWidget *clock;
5 GtkBuilder *build;
6
7 build = gtk_builder_new_from_resource ("/com/github/ToshioCP/tfc/tfc.ui");
8 win = GTK_WIDGET (gtk_builder_get_object (build, "win"));
9 gtk_window_set_application (GTK_WINDOW (win), GTK_APPLICATION (app));
10
11 clock = GTK_WIDGET (gtk_builder_get_object (build, "clock"));
12 g_object_unref(build);
13
14 gtk_drawing_area_set_draw_func(GTK_DRAWING_AREA (clock), draw_clock, NULL, NULL);
15 g_timeout_add(1000, (GSourceFunc) time_handler, (gpointer) clock);
16 gtk_widget_show(win);
17
18 }
Our time_handler() function is very simple, as it just calls
gtk_widget_queue_draw() which schedules a redraw of the widget.
1 gboolean
2 time_handler(GtkWidget* widget) {
3 gtk_widget_queue_draw(widget);
4
5 return TRUE;
6 }
.. and that is all there is to it. If you compile and run the example you will get a ticking analog clock.
If you get this working, you can try modifying some of the code in
draw_clock() to tweak the application (such as change the color or size and
length of the hands) or even add text, or create a digital clock.
The Complete code
You can find the source files in the tfc directory. it can be compiled with ./comp tfc.
tfc.c
1 #include <gtk/gtk.h>
2 #include <math.h>
3 #include <time.h>
4
5 float m_radius = 0.42;
6 float m_line_width = 0.05;
7
8 static void
9 draw_clock (GtkDrawingArea *area, cairo_t *cr, int width, int height, gpointer user_data) {
10
11 // Scale to unit square and translate (0, 0) to be (0.5, 0.5), i.e.
12 // the center of the window
13 cairo_scale(cr, width, height);
14 cairo_translate(cr, 0.5, 0.5);
15
16 // Set the line width and save the cairo drawing state.
17 cairo_set_line_width(cr, m_line_width);
18 cairo_save(cr);
19
20 // Set the background to a slightly transparent green.
21 cairo_set_source_rgba(cr, 0.337, 0.612, 0.117, 0.9); // green
22 cairo_paint(cr);
23
24 // Resore back to precious drawing state and draw the circular path
25 // representing the clockface. Save this state (including the path) so we
26 // can reuse it.
27 cairo_restore(cr);
28 cairo_arc(cr, 0.0, 0.0, m_radius, 0.0, 2.0 * M_PI);
29 cairo_save(cr);
30
31 // Fill the clockface with white
32 cairo_set_source_rgba(cr, 1.0, 1.0, 1.0, 0.8);
33 cairo_fill_preserve(cr);
34 // Restore the path, paint the outside of the clock face.
35 cairo_restore(cr);
36 cairo_stroke_preserve(cr);
37 // Set the 'clip region' to the inside of the path (fill region).
38 cairo_clip(cr);
39
40 // Clock ticks
41 for (int i = 0; i < 12; i++)
42 {
43 // Major tick size
44 double inset = 0.05;
45
46 // Save the graphics state, restore after drawing tick to maintain pen
47 // size
48 cairo_save(cr);
49 cairo_set_line_cap(cr, CAIRO_LINE_CAP_ROUND);
50
51 // Minor ticks are shorter, and narrower.
52 if(i % 3 != 0)
53 {
54 inset *= 0.8;
55 cairo_set_line_width(cr, 0.03);
56 }
57
58 // Draw tick mark
59 cairo_move_to(
60 cr,
61 (m_radius - inset) * cos (i * M_PI / 6.0),
62 (m_radius - inset) * sin (i * M_PI / 6.0));
63 cairo_line_to(
64 cr,
65 m_radius * cos (i * M_PI / 6.0),
66 m_radius * sin (i * M_PI / 6.0));
67 cairo_stroke(cr);
68 cairo_restore(cr); /* stack-pen-size */
69 }
70
71 // Draw the analog hands
72
73 // Get the current Unix time, convert to the local time and break into time
74 // structure to read various time parts.
75 time_t rawtime;
76 time(&rawtime);
77 struct tm * timeinfo = localtime (&rawtime);
78
79 // Calculate the angles of the hands of our clock
80 double hours = timeinfo->tm_hour * M_PI / 6.0;
81 double minutes = timeinfo->tm_min * M_PI / 30.0;
82 double seconds = timeinfo->tm_sec * M_PI / 30.0;
83
84 // Save the graphics state
85 cairo_save(cr);
86 cairo_set_line_cap(cr, CAIRO_LINE_CAP_ROUND);
87
88 cairo_save(cr);
89
90 // Draw the seconds hand
91 cairo_set_line_width(cr, m_line_width / 3.0);
92 cairo_set_source_rgba(cr, 0.7, 0.7, 0.7, 0.8); // gray
93 cairo_move_to(cr, 0.0, 0.0);
94 cairo_line_to(cr,
95 sin(seconds) * (m_radius * 0.9),
96 -cos(seconds) * (m_radius * 0.9));
97 cairo_stroke(cr);
98 cairo_restore(cr);
99
100 // Draw the minutes hand
101 cairo_set_source_rgba(cr, 0.117, 0.337, 0.612, 0.9); // blue
102 cairo_move_to(cr, 0, 0);
103 cairo_line_to(cr,
104 sin(minutes + seconds / 60) * (m_radius * 0.8),
105 -cos(minutes + seconds / 60) * (m_radius * 0.8));
106 cairo_stroke(cr);
107
108 // draw the hours hand
109 cairo_set_source_rgba(cr, 0.337, 0.612, 0.117, 0.9); // green
110 cairo_move_to(cr, 0.0, 0.0);
111 cairo_line_to(cr,
112 sin(hours + minutes / 12.0) * (m_radius * 0.5),
113 -cos(hours + minutes / 12.0) * (m_radius * 0.5));
114 cairo_stroke(cr);
115 cairo_restore(cr);
116
117 // Draw a little dot in the middle
118 cairo_arc(cr, 0.0, 0.0, m_line_width / 3.0, 0.0, 2.0 * M_PI);
119 cairo_fill(cr);
120 }
121
122
123 gboolean
124 time_handler(GtkWidget* widget) {
125 gtk_widget_queue_draw(widget);
126
127 return TRUE;
128 }
129
130
131 static void
132 app_activate (GApplication *app, gpointer user_data) {
133 GtkWidget *win;
134 GtkWidget *clock;
135 GtkBuilder *build;
136
137 build = gtk_builder_new_from_resource ("/com/github/ToshioCP/tfc/tfc.ui");
138 win = GTK_WIDGET (gtk_builder_get_object (build, "win"));
139 gtk_window_set_application (GTK_WINDOW (win), GTK_APPLICATION (app));
140
141 clock = GTK_WIDGET (gtk_builder_get_object (build, "clock"));
142 g_object_unref(build);
143
144 gtk_drawing_area_set_draw_func(GTK_DRAWING_AREA (clock), draw_clock, NULL, NULL);
145 g_timeout_add(1000, (GSourceFunc) time_handler, (gpointer) clock);
146 gtk_widget_show(win);
147
148 }
149
150 static void
151 app_open (GApplication *app, GFile **files, gint n_files, gchar *hint, gpointer user_data) {
152 app_activate(app,user_data);
153 }
154
155 int
156 main (int argc, char **argv) {
157 GtkApplication *app;
158 int stat;
159
160 app = gtk_application_new ("com.github.ToshioCP.tfc", G_APPLICATION_HANDLES_OPEN);
161 g_signal_connect (app, "activate", G_CALLBACK (app_activate), NULL);
162 g_signal_connect (app, "open", G_CALLBACK (app_open), NULL);
163 stat = g_application_run (G_APPLICATION (app), argc, argv);
164 g_object_unref (app);
165 return stat;
166 }
tfc.ui
1 <?xml version="1.0" encoding="UTF-8"?>
2 <interface>
3 <object class="GtkApplicationWindow" id="win">
4 <property name="title">Clock</property>
5 <property name="default-width">200</property>
6 <property name="default-height">200</property>
7 <child>
8 <object class="GtkDrawingArea" id="clock">
9 <property name="hexpand">TRUE</property>
10 <property name="vexpand">TRUE</property>
11 </object>
12 </child>
13 </object>
14 </interface>
tfc.gresource.xml
1 <?xml version="1.0" encoding="UTF-8"?>
2 <gresources>
3 <gresource prefix="/com/github/ToshioCP/tfc">
4 <file>tfc.ui</file>
5 </gresource>
6 </gresources>
comp
1 glib-compile-resources $1.gresource.xml --target=$1.gresource.c --generate-source
2 gcc `pkg-config --cflags gtk4` $1.gresource.c $1.c `pkg-config --libs gtk4` -lm
Up: Readme.md, Prev: Section 22, Next: Section 24