Expose screenshooting as an interface, drop SIGUSR hack.

This pulls in a bit of extra infrastructure for discovering adertised objects on the
client side.

screenshot.c

@@ -0,0 +1,84 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <fcntl.h>
+#include <glib.h>
+
+#include "wayland-client.h"
+#include "wayland-glib.h"
+
+/* The screenshooter is a good example of a custom object exposed by
+ * the compositor and serves as a test bed for implementing client
+ * side marshalling outside libwayland.so */
+
+static const char socket_name[] = "\0wayland";
+
+struct screenshooter {
+	uint32_t id;
+	struct wl_display *display;
+};
+
+static struct screenshooter *
+screenshooter_create(struct wl_display *display)
+{
+	struct screenshooter *screenshooter;
+	uint32_t id;
+
+	id = wl_display_get_object_id(display, "screenshooter");
+	if (id == 0) {
+		fprintf(stderr, "server doesn't support screenshooter interface\n");
+		return NULL;
+	}
+
+	screenshooter = malloc(sizeof screenshooter);
+	if (screenshooter == NULL)
+		return NULL;
+
+	screenshooter->id = id;
+	screenshooter->display = display;
+
+	return screenshooter;
+}
+
+#define SCREENSHOOTER_SHOOT 0
+
+static void
+screenshooter_shoot(struct screenshooter *screenshooter)
+{
+	uint32_t request[2];
+
+	request[0] = screenshooter->id;
+	request[1] = SCREENSHOOTER_SHOOT | ((sizeof request) << 16);
+
+	wl_display_write(screenshooter->display,
+			 request, sizeof request);
+}
+
+int main(int argc, char *argv[])
+{
+	struct wl_display *display;
+	GMainLoop *loop;
+	GSource *source;
+	struct screenshooter *s;
+
+	display = wl_display_create(socket_name);
+	if (display == NULL) {
+		fprintf(stderr, "failed to create display: %m\n");
+		return -1;
+	}
+
+	loop = g_main_loop_new(NULL, FALSE);
+	source = wayland_source_new(display);
+	g_source_attach(source, NULL);
+
+	s = screenshooter_create(display);
+	if (s == NULL)
+		exit(-1);
+
+	screenshooter_shoot(s);
+
+	g_main_loop_run(loop);
+
+	return 0;
+}