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