buffer: introduce wlr_readonly_data_buffer

types/wlr_buffer.c

@@ -451,3 +451,80 @@ struct wlr_shm_client_buffer *shm_client_buffer_create(
 
 	return buffer;
 }
+
+static const struct wlr_buffer_impl readonly_data_buffer_impl;
+
+static struct wlr_readonly_data_buffer *readonly_data_buffer_from_buffer(
+		struct wlr_buffer *buffer) {
+	assert(buffer->impl == &readonly_data_buffer_impl);
+	return (struct wlr_readonly_data_buffer *)buffer;
+}
+
+static void readonly_data_buffer_destroy(struct wlr_buffer *wlr_buffer) {
+	struct wlr_readonly_data_buffer *buffer =
+		readonly_data_buffer_from_buffer(wlr_buffer);
+	free(buffer->saved_data);
+	free(buffer);
+}
+
+static bool readonly_data_buffer_begin_data_ptr_access(struct wlr_buffer *wlr_buffer,
+		void **data, uint32_t *format, size_t *stride) {
+	struct wlr_readonly_data_buffer *buffer =
+		readonly_data_buffer_from_buffer(wlr_buffer);
+	if (buffer->data == NULL) {
+		return false;
+	}
+	*data = (void*)buffer->data;
+	*format = buffer->format;
+	*stride = buffer->stride;
+	return true;
+}
+
+static void readonly_data_buffer_end_data_ptr_access(struct wlr_buffer *wlr_buffer) {
+	// This space is intentionally left blank
+}
+
+static const struct wlr_buffer_impl readonly_data_buffer_impl = {
+	.destroy = readonly_data_buffer_destroy,
+	.begin_data_ptr_access = readonly_data_buffer_begin_data_ptr_access,
+	.end_data_ptr_access = readonly_data_buffer_end_data_ptr_access,
+};
+
+struct wlr_readonly_data_buffer *readonly_data_buffer_create(uint32_t format,
+		size_t stride, uint32_t width, uint32_t height, const void *data) {
+	struct wlr_readonly_data_buffer *buffer = calloc(1, sizeof(*buffer));
+	if (buffer == NULL) {
+		return NULL;
+	}
+	wlr_buffer_init(&buffer->base, &readonly_data_buffer_impl, width, height);
+
+	buffer->data = data;
+	buffer->format = format;
+	buffer->stride = stride;
+
+	return buffer;
+}
+
+bool readonly_data_buffer_drop(struct wlr_readonly_data_buffer *buffer) {
+	bool ok = true;
+
+	if (buffer->base.n_locks > 0) {
+		size_t size = buffer->stride * buffer->base.height;
+		buffer->saved_data = malloc(size);
+		if (buffer->saved_data == NULL) {
+			wlr_log_errno(WLR_ERROR, "Allocation failed");
+			ok = false;
+			buffer->data = NULL;
+			// We can't destroy the buffer, or we risk use-after-free in the
+			// consumers. We can't allow accesses to buffer->data anymore, so
+			// set it to NULL and make subsequent begin_data_ptr_access()
+			// calls fail.
+		} else {
+			memcpy(buffer->saved_data, buffer->data, size);
+			buffer->data = buffer->saved_data;
+		}
+	}
+
+	wlr_buffer_drop(&buffer->base);
+	return ok;
+}