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Hierarchy
The hierarchical drawing structure is an important organizational tool. There is a strong relationship between the organization of the drawing and the organization of the information about the drawing. A block can be used to store information about the group of entities contained in the block. Information about an elementary entity can be stored with that entity.
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Tags
Tags are normally a better means for storing information than schemas. They are faster to access and do not depend on an external library.
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Entity Names
The names given to entities in a drawing are important. Suppose that a drawing consists of rooms where each room is a block. Further suppose that each room contains walls and doors, where each door is a block containing hinges, a doorknob and a panel. If all of the doorknobs are given a common prefix, then a wildcard can be used to isolate doorknobs (i.e., to make doorknobs visible and all other entities invisible). If common prefixes are also used for the other entities, then it is a simple matter to make walls and doors visible and hinges and doorknobs invisible.
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Control of Screen Refresh
Consider the following sequence of commands:
Command Script
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sweep linear polygon \obj1.3 points 0,0,0 0,0,-10 name box
view select isometric front right top
zoom object \box
hide object \box hidden-line
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When these commands are executed, the user would first see a sweep operation, followed by a change of view, followed by a zoom to the object, followed by hidden-line removal; probably a lot of unnecessary screen activity.
The control variable CV_REFRESH can be used with cv_set to control screen refreshes. When refresh is off, commands will execute without disturbing the contents of the screen. The following avoids unnecessary screen refresh:
C / C++ Code
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cv_set (CV_REFRESH,0)
ss_command(“sweep linear polygon \\obj1.3 points 0,0,0 0,0,-10 name box”);
ss_command (“view select isometric front right top”);
ss_command (“zoom object \\box”);
cv_set (CV_REFRESH,1);
ss_command (“hide object \\box hidden-line”);
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Wildcards
It often occurs that an object of a certain type, say a doorknob, is to be picked by the user. The function to accomplish this is pick_entity . Unfortunately, pick_entity is not particularly clever. This function will pick the nearest visible object whether it be a doorknob or a light bulb.
A nice solution is the following:
C / C++ Code
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cv_set ( CV_REFRESH, 0 );_
ss_command (“isolate object !knob*”);
if ( pick_entity ( "Pick doorknob", BITS_OBJECT, path ) )
...
else
...
ss_command (“isolate reset”);
cv_set (CV_REFRESH, 1 );
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The trick is to isolate those objects that are candidates for selection without disturbing the screen. Once the pick has been made, isolation can be reset, again without disturbing the screen.
record_visibility is also a useful function in this context.
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Annotation Environment
Many applications require a specific annotation environment. This can be handled by loading a private annotation environment.
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