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Storage library

This library provides a medium-level interface for accessing and manipulating file contents in memory. Its purpose is to allow code parts developed independently from each other to use the same memory representation of objects while being able to rely on some invariants. In particular, it should be possible to access and manipulate objects without knowledge of the other modules' object system or metadata.

In practice, this means:

The library's interface is designed to anticipate the operations which an application will typically perform on the file's contents and provide abstract functions which express these intentions to allow the library to do some optimization. For example, to delete all circles and arcs with radius zero, instead of

xorn_object_t *objects;
size_t count;
unsigned int i;
xorn_get_objects(rev, &objects, &count);
for (i = 0; i < count; i++) {
xorn_obtype_t type = xorn_get_object_type(rev, objects[i]);
if (type == xornsch_obtype_circle &&
xornsch_get_circle_data(rev, objects[i])->radius == 0.)
xorn_delete_object(rev, objects[i]);
if (type == xornsch_obtype_arc &&
xornsch_get_arc_data(rev, objects[i])->radius == 0.)
xorn_delete_object(rev, objects[i]);
}
free(objects);

you would write:

xorn_selection_t sel = xornsch_select_by_radius(rev, 0.);

The implementation could now, for example, choose to express the selection as a filter which can be applied to individual objects rather than as a list of object pointers, if this should prove more efficient. This way, the application doesn't have to know about but can still benefit from optimizations to the potentially messy detail of how the data is internally stored and accessed.

See also
xornstorage.h
How to use the storage library

Copyright (C) 2013-2016 Roland Lutz

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts.