On 18.03.2013 10:51, memoryl...@tin.it wrote:
> Hi all,
> just to have confirmation of what I am doing.
> My app is multithreaded ; the main() loop and some other working threads,
> receiving / sending data and doing calculations.
>
> The question: what is the correct way to fire a graphics update from a thread
> ?
>
> My work (omitted all sanity checks):
>
> - main:
> .....
> static int fd_refresh[2];
> .....
> pipe(fd_refresh);
> SetNonblocking(fd_refresh[0]);
> SetNonblocking(fd_refresh[1]);
> Fl::add_fd(fd_refresh[0], Do_refresh_callback, NULL);
> .....
> #define CMD_REFRESH 0
> .....
> static void Do_refresh_callback(int fd, void *data)
> {
> unsigned int val;
> while(read(fd, &val, sizeof(val)) > 0)
> {
> switch(val)
> {
> case CMD_REFRESH:
> // HERE I can draw to screen !
<nitpick on>
To be precise: no, you can't!
</nitpick>
You can do widget updates and call redraw(), but you must not
call draw() methods directly from a callback. See also below.
> break;
> .....
> }
> }
> .....
> }
>
> - A thread receives data and wants to update a drawing. It cannot do it
> directly,
> so it writes to fd_refresh[1] an integer which values represent what I want
> to do
> (full redraw(), partial updates, etc.) .
> Fltk then will call Do_refresh_callback and there I will be safe drawing
> anything.
>
> Is this sequence correct ?
> Now it's working without (apparent) problems.
AFAICT this is okay, so long as you don't call draw() directly,
as I wrote above.
However, using Fl::add_fd() with a pipe is not portable. IIRC you're
using an embedded Linux platform, so this may not be a problem for you.
But there are maybe more simple and portable ways using Fl::lock() and
Fl::awake() to send messages from a thread to the FLTK main loop to do
what you need. You can read more about this in the chapter "Advanced
FLTK" in the docs.
http://www.fltk.org/doc-1.3/advanced.html
Others will probably chime in and tell you more about programming with
threads and FLTK.
Albrecht
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