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BOS_NODE
Although the structure for each type of entity is unique, there is a structural prefix that is common to all entity types. For convenience, these common fields are defined as an independent structure called the BOS_NODE . Informally, we speak of the of entity nodes as being BOS nodes. In actuality, there is no entity whose structure corresponds exactly with the structure of the BOS_NODE . Here is the BOS_NODE structure:
C / C++ Code
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BOS_NODE
{
int bits1;
int bits2;
SS_XYZ high;
SS_XYZ low;
SS_XYZ center;
SS_XYZ top_axis;
SS_XYZ bottom_axis;
SS_XYZ local_horz;
SS_XYZ local_vert;
SS_XYZ local_base;
NAME name;
int force_style_color;
RGB force_rgb;
BOS_NODE *next_bos;
BOS_NODE *prev_bos;
BLOCK_NODE *parent;
};
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This structure contains:
Element
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Description
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bits1, bits2
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entity type and entity information.
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high, low
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extent information for the entity.
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name
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the name of the entity.
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center
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the base point used in scaling and rotation.
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top_axis, bottom_axis
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the axis used in axial rotation.
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local_horz, local_vert, local_base
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e-space information for entity.
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next_bos
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a pointer to the next entity within the block.
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prev_bos
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a pointer to the previous entity within the block.
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parent
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a pointer to the parent block.
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An entity may be a block, an object, a symbol, a detail, or a text line. To distinguish between the different entity types, the bits1 field in the BOS_NODE can be examined. A specific bit of this field is set for each of the five entity types. The BITS_OBJECT bit (0x0002) is used to identify objects. If this bit is set then the entity is an object. Similar bit settings are defined in SSNODES.H for the other entity types:
C / C++ Code
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#define BITS_BLOCK 0x0001
#define BITS_OBJECT 0x0002
#define BITS_SYMBOL 0x0004
#define BITS_TEXT 0x0400
#define BITS_DETAIL 0x0100
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Here is an example showing how entities might be identified:
C / C++ Code
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BOS_NODE *bos;
if ( bos->bits1 & BITS_BLOCK )
ss_command (“note This is a block”);
else if ( bos->bits1 & BITS_OBJECT )
ss_command(“note This is an object”);
else if ( bos->bits1 & BITS_SYMBOL )
ss_command(“note This is a symbol”);
else if ( bos->bits1 & BITS_TEXT )
ss_command(“note This is text”);
else if ( bos->bits1 & BITS_DETAIL )
ss_command(“note This is a detail”);
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The annotation block (A-Block) has a special purpose within the SilverScreen hierarchical structure. This type of block is used to store the details (and possibly other entities) that belong to a specific annotation block. A-blocks always appear at the root and can be identified through the bits2 field and the BITS_ANNOTATE definition. An A-Block is identified below:
C / C++ Code
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BOS_NODE *bos;
if ( bos->bits1 & BITS_BLOCK )
{
if ( bos->bits2 & BITS_ANNOTATE )
ss_command (“note This is an annotation block”);
else
ss_command(“note This is not an annotation block”);
}
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BLOCK_NODE
The BLOCK_NODE structure is shown below. Note that the first portion of the structure is identical to that of the BOS_NODE.
C / C++ Code
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BLOCK_NODE
{
int bits1;
int bits2;
SS_XYZ high;
SS_XYZ low;
SS_XYZ center;
SS_XYZ top_axis;
SS_XYZ bottom_axis;
SS_XYZ local_horz;
SS_XYZ local_vert;
SS_XYZ local_base;
NAME name;
int force_style_color;
RGB force_rgb;
BOS_NODE *next_bos;
BOS_NODE *prev_bos;
BLOCK_NODE *parent;
BOS_NODE *first_bos;
SCHEMA_NODE *first_schema;
void *unused1;
};
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The BLOCK_NODE structure contains first_bos , a pointer to the first entity within the block.
To access the entities within a block, the first_bos pointer is used to locate the first entity of the block. Once this first entity has been located, the next_bos pointer can then be used to traverse the list of entities within the block. The list terminates with a null pointer.
The following will display the entity names of a drawing in in-order sequence. Note that the function display_block is used recursively.
C / C++ Code
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#include "silver.h"
#include "ssnodes.h"
. . .
BLOCK_NODE *root;
// Get pointer to root of tree
root = (BLOCK_NODE *) get_bos ( "\\" );
display_block( root );
. . .
void display_block( BLOCK_NODE *blk )
{
BOS_NODE *bos;
ss_command ( "note Block Name: %s", bos->parent?bos->name:”ROOT” );
for ( bos = blk->first_bos ; bos ; bos = bos->next_bos )
{
if ( bos->bits1 & BITS_BLOCK )
display_block( (BLOCK_NODE *)bos );
else
ss_command ( "note name: %s", bos->name );
}
}
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Note the manner in which the BOS_NODE pointer bos is cast to a BLOCK_NODE pointer. This technique is frequently used in accessing drawing structures. That is, the bits of the BOS_NODE are examined to determine the entity type of the node. If the bit setting in bits1 corresponds to that of an OBJECT_NODE , then the BOS_NODE pointer is cast to an OBJECT_NODE pointer.
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