pool-buffer.c

#define _POSIX_C_SOURCE 200112L
#include <cairo/cairo.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>

#include "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[] = "/grim-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);
  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->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;
}