feat(screencopy): add buffer creation through screencopy

include/screencopy.h

@@ -20,4 +20,5 @@ void screencopy_frame_handle_ready(void *data,
 void screencopy_frame_handle_failed(void *data,
                                     struct zwlr_screencopy_frame_v1 *frame);
 bool screencopy_init(struct swappy_state *state);
+void screencopy_destroy_buffer(struct swappy_buffer *buffer);
 bool screencopy_parse_geometry(struct swappy_state *state);

include/swappy.h

@@ -82,7 +82,13 @@ struct swappy_state {
   char **argv;
 };
 
-struct swappy_buffer;
+struct swappy_buffer {
+  struct wl_buffer *wl_buffer;
+  void *data;
+  int32_t width, height, stride;
+  size_t size;
+  enum wl_shm_format format;
+};
 
 struct swappy_output {
   struct swappy_state *state;

src/screencopy.c

@@ -1,18 +1,104 @@
 #include "screencopy.h"
 
+#include <errno.h>
+#include <fcntl.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
+#include <sys/mman.h>
 #include <wayland-client.h>
 
 #include "box.h"
 #include "swappy.h"
 #include "wlr-screencopy-unstable-v1-client-protocol.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[] = "/swappy-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 struct swappy_buffer *create_buffer(struct wl_shm *shm,
                                            enum wl_shm_format format,
                                            int32_t width, int32_t height,
                                            int32_t stride) {
-  return NULL;
+  size_t size = stride * height;
+  g_debug("creating buffer with dimensions: %dx%d", width, height);
+
+  int fd = create_shm_file(size);
+  if (fd == -1) {
+    return NULL;
+  }
+
+  void *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);
+  struct wl_buffer *wl_buffer =
+      wl_shm_pool_create_buffer(pool, 0, width, height, stride, format);
+  wl_shm_pool_destroy(pool);
+
+  close(fd);
+
+  struct swappy_buffer *buffer = calloc(1, sizeof(struct swappy_buffer));
+  buffer->wl_buffer = wl_buffer;
+  buffer->data = data;
+  buffer->width = width;
+  buffer->height = height;
+  buffer->stride = stride;
+  buffer->size = size;
+  buffer->format = format;
+
+  return buffer;
+}
+
+void screencopy_destroy_buffer(struct swappy_buffer *buffer) {
+  if (buffer == NULL) {
+    return;
+  }
+  munmap(buffer->data, buffer->size);
+  wl_buffer_destroy(buffer->wl_buffer);
+  free(buffer);
 }
 
 void screencopy_frame_handle_buffer(void *data,
@@ -29,7 +115,7 @@ void screencopy_frame_handle_buffer(void *data,
     exit(EXIT_FAILURE);
   }
 
-  //  zwlr_screencopy_frame_v1_copy(frame, output->buffer->wl_buffer);
+    zwlr_screencopy_frame_v1_copy(frame, output->buffer->wl_buffer);
 }
 
 void screencopy_frame_handle_flags(void *data,

src/wayland.c

@@ -252,6 +252,7 @@ void wayland_finish(struct swappy_state *state) {
       zxdg_output_v1_destroy(output->xdg_output);
     }
     wl_output_release(output->wl_output);
+    screencopy_destroy_buffer(output->buffer);
     free(output);
   }