pool-buffer.c

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/* SPDX-License-Identifier: BSD-3-Clause */
 
#define _POSIX_C_SOURCE 200112L
#include <cairo/cairo.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#include <wayland-client.h>
#include <string.h>
 
#include "pool-buffer.h"
 
static void randname(char *buf) {
    struct timespec ts;
    clock_gettime(CLOCK_REALTIME, &ts);
    long r = ts.tv_nsec;
    for (int i = 0; i < 6; ++i) {
        buf[i] = 'A'+(r&15)+(r&16)*2;
        r >>= 5;
    }
}
 
static int anonymous_shm_open(void) {
    char name[] = "/dunst-XXXXXX";
    int retries = 100;
 
    do {
        randname(name + strlen(name) - 6);
 
        --retries;
        // shm_open guarantees that O_CLOEXEC is set
        int fd = shm_open(name, O_RDWR | O_CREAT | O_EXCL, 0600);
        if (fd >= 0) {
            shm_unlink(name);
            return fd;
        }
    } while (retries > 0 && errno == EEXIST);
 
    return -1;
}
 
static int create_shm_file(off_t size) {
    int fd = anonymous_shm_open();
    if (fd < 0) {
        return fd;
    }
 
    if (ftruncate(fd, size) < 0) {
        close(fd);
        return -1;
    }
 
    return fd;
}
 
static void buffer_handle_release(void *data, struct wl_buffer *wl_buffer) {
    struct pool_buffer *buffer = data;
    buffer->busy = false;
}
 
static const struct wl_buffer_listener buffer_listener = {
    .release = buffer_handle_release,
};
 
static struct pool_buffer *create_buffer(struct wl_shm *shm,
        struct pool_buffer *buf, int32_t width, int32_t height) {
    const enum wl_shm_format wl_fmt = WL_SHM_FORMAT_ARGB8888;
    const cairo_format_t cairo_fmt = CAIRO_FORMAT_ARGB32;
 
    uint32_t stride = cairo_format_stride_for_width(cairo_fmt, width);
    size_t size = stride * height;
 
    void *data = NULL;
    if (size > 0) {
        int fd = create_shm_file(size);
        if (fd == -1) {
            return NULL;
        }
 
        data = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
        if (data == MAP_FAILED) {
            close(fd);
            return NULL;
        }
 
        struct wl_shm_pool *pool = wl_shm_create_pool(shm, fd, size);
        buf->buffer =
            wl_shm_pool_create_buffer(pool, 0, width, height, stride, wl_fmt);
        wl_buffer_add_listener(buf->buffer, &buffer_listener, buf);
        wl_shm_pool_destroy(pool);
 
        close(fd);
    }
 
    buf->data = data;
    buf->size = size;
    buf->width = width;
    buf->height = height;
    buf->surface = cairo_image_surface_create_for_data(data, cairo_fmt, width,
        height, stride);
    buf->cairo = cairo_create(buf->surface);
    buf->pango = pango_cairo_create_context(buf->cairo);
    return buf;
}
 
void finish_buffer(struct pool_buffer *buffer) {
    if (buffer->buffer) {
        wl_buffer_destroy(buffer->buffer);
    }
    if (buffer->cairo) {
        cairo_destroy(buffer->cairo);
    }
    if (buffer->surface) {
        cairo_surface_destroy(buffer->surface);
    }
    if (buffer->pango) {
        g_object_unref(buffer->pango);
    }
    if (buffer->data) {
        munmap(buffer->data, buffer->size);
    }
    memset(buffer, 0, sizeof(struct pool_buffer));
}
 
struct pool_buffer *get_next_buffer(struct wl_shm *shm,
        struct pool_buffer pool[static 2], uint32_t width, uint32_t height) {
    struct pool_buffer *buffer = NULL;
    for (size_t i = 0; i < 2; ++i) {
        if (pool[i].busy) {
            continue;
        }
        buffer = &pool[i];
    }
    if (!buffer) {
        return NULL;
    }
 
    if (buffer->width != width || buffer->height != height) {
        finish_buffer(buffer);
    }
 
    if (!buffer->buffer) {
        if (!create_buffer(shm, buffer, width, height)) {
            return NULL;
        }
    }
 
    return buffer;
}