dblbuf.c File Reference

#include "dblbuf.h"
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <libbase/libbase.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>
#include <wayland-client-protocol.h>

Include dependency graph for dblbuf.c:

Classes
struct	wlcl_buffer_t
struct	_wlcl_dblbuf_t

Macros
#define	_WLCL_DBLBUF_NUM   2

Functions
static void	_wlcl_dblbuf_callback_if_ready (wlcl_dblbuf_t *dblbuf_ptr)
static void	_wlcl_dblbuf_handle_frame_done (void *data_ptr, struct wl_callback *callback, uint32_t time)
static bool	_wlcl_dblbuf_create_buffer (wlcl_buffer_t *buffer_ptr, wlcl_dblbuf_t *dblbuf_ptr, struct wl_shm_pool *wl_shm_pool_ptr, unsigned page, unsigned width, unsigned height)
static void	_wlcl_dblbuf_handle_wl_buffer_release (void *data_ptr, struct wl_buffer *wl_buffer_ptr)
static int	_wlcl_dblbuf_shm_create (const char *app_id_ptr, size_t size)
wlcl_dblbuf_t *	wlcl_dblbuf_create (const char *app_id_ptr, struct wl_surface *wl_surface_ptr, struct wl_shm *wl_shm_ptr, unsigned width, unsigned height)
void	wlcl_dblbuf_destroy (wlcl_dblbuf_t *dblbuf_ptr)
void	wlcl_dblbuf_register_ready_callback (wlcl_dblbuf_t *dblbuf_ptr, wlcl_dblbuf_ready_callback_t callback, void *callback_ud_ptr)

Variables
static const uint32_t	SHM_OPEN_RETRIES = 256
static const struct wl_buffer_listener	_wlcl_dblbuf_wl_buffer_listener
static const struct wl_callback_listener	_wlcl_dblbuf_frame_listener

Detailed Description

Copyright

Copyright 2025 Google LLC

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Macro Definition Documentation

_WLCL_DBLBUF_NUM

#define _WLCL_DBLBUF_NUM   2

How many buffers to hold for the double buffer: Two.

Function Documentation

_wlcl_dblbuf_callback_if_ready()

void _wlcl_dblbuf_callback_if_ready ( wlcl_dblbuf_t * dblbuf_ptr )

static

Calls wlcl_dblbuf_t::callback, if it is registered, a frame is due, and if there are available buffers. If so, and if the callback returns true, the corresponding buffer will be attached to the surface and the surface is committed.

Parameters

dblbuf_ptr

_wlcl_dblbuf_create_buffer()

bool _wlcl_dblbuf_create_buffer ( wlcl_buffer_t * buffer_ptr, wlcl_dblbuf_t * dblbuf_ptr, struct wl_shm_pool * wl_shm_pool_ptr, unsigned page, unsigned width, unsigned height )

static

Helper: Creates a struct wl_buffer from the wl_shm_pool_ptr at given dimensions and page number, and stores all into buffer_ptr.

Parameters

buffer_ptr
dblbuf_ptr
wl_shm_pool_ptr
page
width
height

Returns

true on success.

_wlcl_dblbuf_handle_frame_done()

void _wlcl_dblbuf_handle_frame_done ( void * data_ptr, struct wl_callback * callback, uint32_t time )

static

Callback for when the compositor indicates a frame is due.

_wlcl_dblbuf_handle_wl_buffer_release()

void _wlcl_dblbuf_handle_wl_buffer_release ( void * data_ptr, struct wl_buffer * wl_buffer_ptr )

static

Handles the release notification of the wl_buffer interface.

Parameters

data_ptr
wl_buffer_ptr

_wlcl_dblbuf_shm_create()

int _wlcl_dblbuf_shm_create ( const char * app_id_ptr, size_t size )

static

Creates a POSIX shared memory object and allocates size bytes to it.

Parameters

app_id_ptr
size

Returns

The file descriptor (a non-negative integer) on success, or -1 on failure. The file descriptor must be closed with close(2).

wlcl_dblbuf_create()

wlcl_dblbuf_t * wlcl_dblbuf_create	(	const char *	app_id_ptr,
		struct wl_surface *	wl_surface_ptr,
		struct wl_shm *	wl_shm_ptr,
		unsigned	width,
		unsigned	height )

Creates a double buffer for the surface with provided dimensions.

Parameters

app_id_ptr
wl_surface_ptr
wl_shm_ptr
width
height

Returns

Pointer to state of the double buffer, or NULL on error. Call wlcl_dblbuf_destroy for freeing up the associated resources.

wlcl_dblbuf_destroy()

void wlcl_dblbuf_destroy

(

wlcl_dblbuf_t *

dblbuf_ptr

)

Destroys the double buffer.

wlcl_dblbuf_register_ready_callback()

void wlcl_dblbuf_register_ready_callback	(	wlcl_dblbuf_t *	dblbuf_ptr,
		wlcl_dblbuf_ready_callback_t	callback,
		void *	callback_ud_ptr )

Registers a callback for when a frame can be drawn into the buffer.

The frame can be drawn if (1) it is due, and (2) there is a back buffer available ("released") for drawing into. If these conditions hold true, callback will be called right away. Otherwise, it will be called once these conditions are fulfilled.

The callback will be called only once. If the client wishes further notifications, they must call wlcl_dblbuf_register_ready_callback again.

The callback must be registered only after the surface is ready. Eg. for an XDG toplevel, after it has received & acknowledged configure.

Parameters

dblbuf_ptr
callback	The callback function, or NULL to clear the callback.
callback_ud_ptr	Argument to use for callback.

Variable Documentation

_wlcl_dblbuf_frame_listener

const struct wl_callback_listener _wlcl_dblbuf_frame_listener

static

Initial value:

                                       = {
    .done = _wlcl_dblbuf_handle_frame_done
}

Listener implementation for the frame.

_wlcl_dblbuf_wl_buffer_listener

const struct wl_buffer_listener _wlcl_dblbuf_wl_buffer_listener

static

Initial value:

                                     = {
    .release = _wlcl_dblbuf_handle_wl_buffer_release,
}

Listener implementation for the wl_buffer.

SHM_OPEN_RETRIES

const uint32_t SHM_OPEN_RETRIES = 256

static

How many attempts to try shm_open before giving up.