Main loop integeration

## Main loop integeration Main loop integeration — Functions for integrating Cogl with an application's main loop |

## Synopsis

    enum                CoglPollFDEvent;
                        CoglPollFD;
    void                cogl_poll_get_info                  (CoglContext *context,
                                                             CoglPollFD **poll_fds,
                                                             int *n_poll_fds,
                                                             gint64 *timeout);
    void                cogl_poll_dispatch                  (CoglContext *context,
                                                             const CoglPollFD *poll_fds,
                                                             int n_poll_fds);
    GSource *           cogl_glib_source_new                (CoglContext *context,
                                                             int priority);

## Description

Cogl needs to integrate with the application's main loop so that it can internally handle some events from the driver. All Cogl applications must use these functions. They provide enough information to describe the state that Cogl will need to wake up on. An application using the GLib main loop can instead use `cogl_glib_source_new()` which provides a GSource ready to be added to the main loop.

## Details

### enum CoglPollFDEvent

    typedef enum {
      COGL_POLL_FD_EVENT_IN = COGL_SYSDEF_POLLIN,
      COGL_POLL_FD_EVENT_PRI = COGL_SYSDEF_POLLPRI,
      COGL_POLL_FD_EVENT_OUT = COGL_SYSDEF_POLLOUT,
      COGL_POLL_FD_EVENT_ERR = COGL_SYSDEF_POLLERR,
      COGL_POLL_FD_EVENT_HUP = COGL_SYSDEF_POLLHUP,
      COGL_POLL_FD_EVENT_NVAL = COGL_SYSDEF_POLLNVAL
    } CoglPollFDEvent;

A bitmask of events that Cogl may need to wake on for a file descriptor. Note that these all have the same values as the corresponding defines for the poll function call on Unix so they may be directly passed to poll.

Since 1.10

Stability Level: Unstable

### CoglPollFD

    typedef struct {
      int fd;
      short int events;
      short int revents;
    } CoglPollFD;

A struct for describing the state of a file descriptor that Cogl needs to block on. The `events` field contains a bitmask of CoglPollFDEvents that should cause the application to wake up. After the application is woken up from idle it should pass back an array of CoglPollFDs to Cogl and update the `revents` mask to the actual events that occurred on the file descriptor.

Note that CoglPollFD is deliberately exactly the same as struct pollfd on Unix so that it can simply be cast when calling poll.

int `fd`; | The file descriptor to block on
short int `events`; | A bitmask of events to block on
short int `revents`; | A bitmask of returned events

Since 1.10

Stability Level: Unstable

### cogl_poll_get_info ()

    void                cogl_poll_get_info                  (CoglContext *context,
                                                             CoglPollFD **poll_fds,
                                                             int *n_poll_fds,
                                                             gint64 *timeout);

This should be called whenever an application is about to go idle so that Cogl has a chance to describe what state it needs to be woken up on. The assumption is that the application is using a main loop with something like the poll function call on Unix or the GLib main loop.

After the function is called *`poll_fds` will contain a pointer to an array of CoglPollFD structs describing the file descriptors that Cogl expects. The fd and events members will be updated accordingly. After the application has completed its idle it is expected to either update the revents members directly in this array or to create a copy of the array and update them there. Either way it should pass a pointer to either array back to Cogl when calling `cogl_poll_dispatch()`.

When using the `COGL_WINSYS_ID_WGL` winsys (where file descriptors don't make any sense) or `COGL_WINSYS_ID_SDL` (where the event handling functions of SDL don't allow blocking on a file descriptor) *n_poll_fds is guaranteed to be zero.

`timeout` will contain a maximum amount of time to wait in microseconds before the application should wake up or -1 if the application should wait indefinitely. This can also be 0 zero if Cogl needs to be woken up immediately.

`context` : | A CoglContext
`poll_fds` : | A return location for a pointer to an array of CoglPollFDs
`n_poll_fds` : | A return location for the number of entries in *`poll_fds`
`timeout` : | A return location for the maximum length of time to wait in microseconds, or -1 to wait indefinitely.

Since 1.10

Stability Level: Unstable

### cogl_poll_dispatch ()

    void                cogl_poll_dispatch                  (CoglContext *context,
                                                             const CoglPollFD *poll_fds,
                                                             int n_poll_fds);

This should be called whenever an application is woken up from going idle in its main loop. The `poll_fds` array should contain a list of file descriptors matched with the events that occurred in revents. The events field is ignored. It is safe to pass in extra file descriptors that Cogl didn't request from `cogl_context_begin_idle()` or a shorter array missing some file descriptors that Cogl requested.

`context` : | A CoglContext
`poll_fds` : | An array of CoglPollFDs describing the events that have occurred since the application went idle.
`n_poll_fds` : | The length of the `poll_fds` array.

Since 1.10

Stability Level: Unstable

### cogl_glib_source_new ()

    GSource *           cogl_glib_source_new                (CoglContext *context,
                                                             int priority);

Creates a GSource which handles Cogl's internal system event processing. This can be used as a convenience instead of `cogl_poll_get_info()` and `cogl_poll_dispatch()` in applications that are already using the GLib main loop. After this is called the GSource should be attached to the main loop using `g_source_attach()`.

`context` : | A CoglContext
`priority` : | The priority of the GSource
Returns : | a new GSource

Since 1.10

Stability Level: Unstable