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154 lines
3.9 KiB
HTML
154 lines
3.9 KiB
HTML
5 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
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"http://www.w3.org/TR/REC-html40/loose.dtd">
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<!-- $Id: ex-script.html 269 2001-10-10 00:38:28Z garland $ -->
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<!-- Based on ../tests/t-script.cxx revision 1.6 -->
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<html>
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<head>
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<title>libgfx: Simple Scripted Program</title>
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<link rel=stylesheet href="cdoc.css" type="text/css">
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<meta name="Author" content="Michael Garland">
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<style type="text/css">
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<!--
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pre { margin-left: 2em }
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-->
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</style>
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</head>
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<body>
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<h2>Simple Scripted Program</h2>
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<p>This program demonstrates some of the basic features provided by the
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<tt>libgfx</tt> <a href="script.html">scripting package</a>. Given a list of
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file names on the command line, it reads each of them in turn and executes the
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scripting commands contained within them.
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<h3>Setup and Initialization</h3>
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<p>The program begins by including the headers for the <tt>libgfx</tt> modules
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which it uses:
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<pre>
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#include <gfx/gfx.h>
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#include <gfx/script.h>
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#include <gfx/vec3.h>
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</pre>
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<p>The <tt>main()</tt> application entry point performs a very simple task.
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It creates a scripting environment (<tt>class CmdEnv</tt> and registers a set
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of scripting commands. Once these handlers have been installed,
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it loops over every file name specified on the command line and executes it as
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a script.
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<pre>
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main(int argc, char *argv[])
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{
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CmdEnv env;
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env.register_command("add", proc_add);
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env.register_command("avg", proc_add);
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env.register_command("echo", proc_echo);
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env.register_command("vec3", proc_vec3);
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for(int i=1; i&argc; i++)
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script_do_file(argv[i], env);
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return 0;
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}
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</pre>
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<h3>Command Procedures</h3>
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<p>Every scripting command is handled by some command procedure. The
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registration code above binds the actual procedures to the names of their
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scripting commands. Then, whenever a given command occurs in a script being
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processed, the corresponding handler is invoked.
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<p>The first command procedure actually implements two scripting commands:
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<tt>add</tt> and <tt>avg</tt>. It determines which command has been invoked
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by examining its <tt>name</tt> argument.
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It treats its command line as a whitespace-separated sequence of numbers,
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either adds or averages all of them, and then prints the result.
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<pre>
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int proc_add(const CmdLine &cmd)
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{
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double sum = 0.0;
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int count;
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std::vector<double> values;
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cmd.collect_as_numbers(values);
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for(count=0; count<values.size(); count++)
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sum += values[count];
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if( cmd.opname() == "avg" && count>0 )
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sum /= (double)count;
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cout << sum << endl;
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return SCRIPT_OK;
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}
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</pre>
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<p>This next procedure requires precisely 3 numeric arguments, from which it
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constructs a 3-D vector using the <tt>Vec3</tt> class. If the number of
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arguments is not 3, it returns a value indicating a syntax error occurred.
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<pre>
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int proc_vec3(const CmdLine &cmd)
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{
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if( cmd.argcount() != 3 ) return SCRIPT_ERR_SYNTAX;
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Vec3 v;
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cmd.collect_as_numbers(v, 3);
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cout << v << endl;
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return SCRIPT_OK;
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}
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</pre>
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<p>Finally, the <tt>echo</tt> procedure does not interpret its arguments at
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all. Instead, it simply prints the entire argument line as is.
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<pre>
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int proc_echo(const CmdLine &cmd)
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{
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cout << cmd.argline() << endl;
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return SCRIPT_OK;
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}
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</pre>
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<h3>Sample Execution</h3>
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<p>To demonstrate the action of this sample program, here is a particularly
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simple script.
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<pre>
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# This is a test script meant to be fed to t-script. It is not meant as an
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# exhaustive test, but mainly as a demonstration.
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echo The following sum should be 15
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add 1 2 3 4 5
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echo
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echo The following average should be 3.5
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avg 3 8 2 1
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echo
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echo The following is the vector [1 0 0]
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vec3 1 0 0
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</pre>
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<p>When given to the sample program, it produces the following output
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<pre>
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The following sum should be 15
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15
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The following average should be 3.5
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3.5
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The following is the vector [1 0 0]
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1 0 0
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</pre>
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</body>
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</html>
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