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<body>
<h1> pcb-rnd hacking - how importers work </h1>
<h2> Introduction </h2>
This document describes the common aspects of import code, be it an
import_ plugin or the load part of an io_plugin, importing a footprint,
loading a board or a netlist.
<h2> Data structures </h2>
The board is stored in pcb_board_t *. Some import code, like the one
that loads a design (an io plugin's ->parse_pcb function), gets the
target in an argument. (Other, non-import code usually operate on
the global variable that represents the current board:
<i>pcb_board_t *PCB.</i>).
<p>
In either case, pcb_board_t's most important field is <i>pcb_data_t *data</i>,
which holds lists and vectors to store <b>all objects on the board</b>. When
the target is a buffer (e.g. io plugin's ->parse_element function), it's
a <i>pcb_buffer_t *buf</i> which also have a <i>pcb_data_t *data</i> containing
the same data a board could.
<p>
A pcb_data_t struct in turn has three sets of important fields:
<ul>
<li> lists for layer-independent objects (e.g. rat lines, padstacks, subcircuits)
<li> number of layers in use (LayerN) and an array of layers (see later)
<li> rtree structures - these are used for looking up objects for locations
</ul>
Each layer is a pcb_layer_t structure. A layer has the following fields:
<ul>
<li> lists for lines, texts, arcs, polygons
<li> some generic layer attributes (colors, flags, key-value pairs)
<li> an rtree struct for each object type.
</ul>
<p>
Any code that needs to create objects should use the functions in obj_*.h.
The functions that operate layer-independently usually get a destination as
<i>pcb_data_t</i>, so they can operate both on boards and buffers. A typical
example is <i>pcb_pstk_t *pcb_pstk_new(pcb_data_t *data, ...)</i> that returns
NULL or the pointer to the new via that is already added to the corresponding list
of data and in the rtree.
<p>
Layer object creation is done referencing the layer as <i>pcb_layer_t *</i>. A
typical example is <i>pcb_line_t *pcb_line_new(pcb_layer_t *layer...)</i>
which returns NULL on error or a pointer to the new line object created (inserted
in the layer's line list, added to the rtree).
<p>
Code should <b>avoid</b> manipulating the lists and rtree structures directly.
<table border=1>
<tr><td><img src="data1.png">
<br>
Figure 1. simplified map of object related data structures
<br>
<small>diamond: variable; rectangle: struct; round: struct field; green: drawing primitive</small>
</table>
<h2> Extra steps around creating a new board </h2>
TODO: postproc, post*, other setup
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