shm.c

/* Portions of this file taken from sway, MIT licensed */
#include <assert.h>
#include <cairo/cairo.h>
#include <errno.h>
#include <fcntl.h>
#include <pango/pangocairo.h>
#include <stdbool.h>
#include <string.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#include <wayland-client.h>
#include "shm.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;
	}
}

int create_shm_file(void) {
	int retries = 100;
	do {
		char name[] = "/wl_shm-XXXXXX";
		randname(name + strlen(name) - 6);

		--retries;
		// CLOEXEC is guaranteed to be set by shm_open
		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;
}

int allocate_shm_file(size_t size) {
	int fd = create_shm_file();
	if (fd < 0) {
		return -1;
	}

	int ret;
	do {
		ret = ftruncate(fd, size);
	} while (ret < 0 && errno == EINTR);
	if (ret < 0) {
		close(fd);
		return -1;
	}

	return fd;
}

static void buffer_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_release
};

struct pool_buffer *create_buffer(struct wl_shm *shm, struct pool_buffer *buf,
		int32_t width, int32_t height, uint32_t format) {
	uint32_t stride = width * 4;
	size_t size = stride * height;

	int fd = allocate_shm_file(size);
	assert(fd != -1);
	void *data = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
	struct wl_shm_pool *pool = wl_shm_create_pool(shm, fd, size);
	buf->buffer = wl_shm_pool_create_buffer(pool, 0,
			width, height, stride, format);
	wl_shm_pool_destroy(pool);
	close(fd);

	buf->size = size;
	buf->width = width;
	buf->height = height;
	buf->data = data;
	buf->surface = cairo_image_surface_create_for_data(data,
			CAIRO_FORMAT_ARGB32, width, height, stride);
	buf->cairo = cairo_create(buf->surface);
	buf->pango = pango_cairo_create_context(buf->cairo);

	wl_buffer_add_listener(buf->buffer, &buffer_listener, buf);
	return buf;
}

void destroy_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) {
		destroy_buffer(buffer);
	}

	if (!buffer->buffer) {
		if (!create_buffer(shm, buffer, width, height,
					WL_SHM_FORMAT_ARGB8888)) {
			return NULL;
		}
	}
	buffer->busy = true;
	return buffer;
}