SilverScreen Solid Modeler

Command System

Command System

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Command System

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SilverScreenAPI

 

Command System

 

 
Script commands are the primary means of communication between programs and the SilverScreen API. The ss_command function, available in C++, SilverSharp and SilverC, sends commands to the engine for processing. In this section we will describe how commands fit into the overall structure of SilverScreen and the API.

A Command-Based System

 
SilverScreen is a fully command-based system.  Every activity, interactive or otherwise, is executed by means of a command.  Below is a schematic that shows the relationship between the three systems that operate within interactive SilverScreen.

 

sysc0

 

r_pointThe user selects from the SilverScreen menu.  On the basis of this selection, a command is sent to the Interactive System.

 

r_pointThe Interactive System interprets the command and requests appropriate information from the user.  Once the user has supplied this information, one or more commands are sent to the Execution System.

 

r_pointThe Execution System interprets and executes the commands.

 

The commands that are passed from the Menu System to the Interactive System are called icommands (interactive commands).  The commands between the Interactive System and the Execution System are simply called commands.  (The word "command" is often used loosely to refer to either a command or an icommand.

Example

 
A user selects Draw Polygon from the menu.  This selection is translated by the Menu System to an icommand and sent to the Interactive System.  Here is the icommand:

 

  icommand draw polygon common

 
When the Interactive System receives this command, it prompts the user for a set of polygon points.  Assume that the user selects five points.  Then the commands sent to the Execution System might be as follows:

Command Script

 

 begin polygon

 point 1,1,10

 point 1,5,10

 point 3,8,10

 point 6,10,10

 point 10,0,10

 end

 

 
These commands will cause the Execution System to draw a polygon on the screen and to include the polygon within the drawing database.

Application Programs and Commands

 
SilverScreen is designed so that the Interactive and Execution Systems are independent of the source of the commands that they process.  That is, these systems do not know whether a command comes from an interactive user or from an application program.

 

Using the ss_command function, a C++, SilverSharp or SilverC application program can send the icommand:

 

C / C++ Code

 

 ss_command("icommand draw polygon common");

 

 

The Interactive System will respond to this icommand exactly as if the icommand were sent from the Menu System.   That is, it will prompt the user for a set of points.  After the user has supplied the points, it will then send commands to the Execution System to draw the polygon.

 

Application programs can also use ss_command to send commands directly to the Execution System.  The following command will rotate an object about the y-axis.

 

C / C++ Code

 

 ss_command( "rotate object \\screw y%d", degrees );

 

 
The important point is this: The full power of SilverScreen, both at the interactive level and the execution level, is available to application programs through commands, icommands, and the ss_command function.