buffer: introduce wlr_buffer_get_data_ptr

The function has been place in an internal header for API stability
reasons.

include/types/wlr_buffer.h

@@ -0,0 +1,15 @@
+#ifndef TYPES_WLR_BUFFER
+#define TYPES_WLR_BUFFER
+
+#include <wlr/types/wlr_buffer.h>
+/**
+ * Access a pointer to the allocated data from the underlying implementation,
+ * and its stride.
+ *
+ * The returned pointer should be pointing to a valid memory location for read
+ * and write operations.
+ */
+bool buffer_get_data_ptr(struct wlr_buffer *buffer, void **data,
+	size_t *stride);
+
+#endif

include/wlr/types/wlr_buffer.h

@@ -19,6 +19,8 @@ struct wlr_buffer_impl {
 	void (*destroy)(struct wlr_buffer *buffer);
 	bool (*get_dmabuf)(struct wlr_buffer *buffer,
 		struct wlr_dmabuf_attributes *attribs);
+	bool (*get_data_ptr)(struct wlr_buffer *buffer, void **data,
+		size_t *stride);
 };
 
 /**

types/wlr_buffer.c

@@ -5,6 +5,7 @@
 #include <wlr/types/wlr_linux_dmabuf_v1.h>
 #include <wlr/util/log.h>
 #include "render/pixel_format.h"
+#include "types/wlr_buffer.h"
 #include "util/signal.h"
 
 void wlr_buffer_init(struct wlr_buffer *buffer,
@@ -65,6 +66,13 @@ bool wlr_buffer_get_dmabuf(struct wlr_buffer *buffer,
 	return buffer->impl->get_dmabuf(buffer, attribs);
 }
 
+bool buffer_get_data_ptr(struct wlr_buffer *buffer, void **data,
+		size_t *size) {
+	if (!buffer->impl->get_data_ptr) {
+		return false;
+	}
+	return buffer->impl->get_data_ptr(buffer, data, size);
+}
 
 bool wlr_resource_is_buffer(struct wl_resource *resource) {
 	return strcmp(wl_resource_get_class(resource), wl_buffer_interface.name) == 0;