Thanks for the helpful replies, but I'm still at a loss. Here's some
more detailed info. I'm sure it's possible to make this work, but am
currently at a loss. In any case, I'll outline the two main methods I'm
trying.
0. Background
--------------
I've got a GTK application which uses a canvas to draw various objects.
It works quite well. I'm trying to add a new object that does video
processing. So basically, I create a button called "start_capture",
which when clicked will start rendering video to a GDK drawing area.
1. Pthread case
----------------
I've got a callback connected to the start_capture button which creates
the "read_video" thread. Here's my "read_video" code:
void *read_video() {
int i, retval;
struct timeval tv;
long newframetime;
while(1) {
printf("reading video\n");
i = -1;
while(i<0) {
i= ioctl(cam,VIDIOCSYNC, &frame);
if(i < 0 && errno == EINTR) continue;
if (i < 0) {
perror ("VIDIOCSYNC");
exit(-1);
}
break;
}
q++;
buf = bigbuf + vidbuf.offsets[frame];
mapbuf.frame = frame;
if (ioctl(cam,VIDIOCMCAPTURE, &mapbuf)<0) {
perror("VIDIOCMCAPTURE");
exit(-1);
}
draw_video_to_darea();
frame++;
}
}
The problem is that since this function never returns, I never get
control back to my application. The start_capture button remains
pressed and my "draw_video_to_darea()" function simply renders video to
the external window / drawing area. I'm at a loss as to how I can set
this up NOT to require a while(1) loop.
If I don't join the thread, I get an Xlib error:
Xlib: unexpected async reply (sequence 0xb4b)!
of course the "sequence" changes. Yes, I am using the gtk_thread_init()
call and the rest. There is no sharing of data in my app (yet) so it's
not a mutex issue.
2. gdk_input_add case
----------------------
If I set the following:
fd = open("/dev/video",O_RDONLY);
gdk_input_add(fd,
GDK_INPUT_READ,
GTK_SIGNAL_FUNC(read_video),
NULL);
NOTHING HAPPENS!!!! I need to open /dev/vbi instead. Of course in this
case, my read_video() function doesn't have the while(1) loop. But the
problem with opening /dev/vbi is that it seems to get VERY FREQUENT
updates. So the gdk scheduler is calling read_video at an incredible
rate. Looks great for video refresh, but bogs down my application.
I've tested out this method w/o rendering the video to a window ... same
problem. So it has something to do with the actual reading / polling of
the video device.
----------------------
I'm looking at the glib functions g_source_add() and whatnot, but they
seem much more involved. Anyone have some decent examples?
Thanks all,
DT
--
Technical Director, Virginia Center for Computer Music
