A great way to learn how to write scripts is by
using the
Script Manager to view the sample scripts supplied
with your Mira installation. You can also setup a productive
learning environment by opening the
Script Editor on one side of the screen and a Mira
Text Editor on the other side of the screen. Text messages can be
sent to the Editor as a result of adding or changing the script,
then running it from the Script Editor. In fact, you should
do exactly this when you read through the example below. Create and
run the script provided below. Then add features, change the code,
and re-run your changes.
Example
In the script below, we create a Mira Text Editor
window with the window caption "My Text Window". Then we use a few
commands to create some values and print them in the window. The
script finishes by deleting the class from memory. This simple
script uses these elements:
Lua
math package (see the
Lua documentation for a description of the math
package).
Class method
CTextView:
Printf to perform C-style formatted text output.
--(green)
is used for inline comments.
The example below provides a complete script. If
you want to run this script, paste the
plain text version into the
Script Editor.
T = new_textview("My Text
Window")
-- create an instance of class
CTextView
n = math.sqrt( GetNumber(100)
)
-- get a number from the user, default to
100
f = n + math.log( n/55.4 )
-- do some math
s = "My String" .. " goes
here."
-- concatenate two strings
T:Printf("Val=%.2f\r\nStr= '%s'\r\n", f,s)
-- format f and s to the Text Editor.
-- (do
more things here)
T:delete()
-- do when completely finished using T
This script has 4 main parts:
The first statement creates a new instance of
the class
CTextView which refers to a Mira Text
Editor window. The CTextView class provides methods for
working with its window. The
new method assigns a name to the window and returns a
reference to the new
CTextView object. The script assigns this
reference to T. To work with this
object later in the script, use a syntax like T:MyMethod() or T:MyData . You could create a second text window
using a syntax like T2 = CTextView:new("My Second Text Window")
Next, the script computes the square root of a
number you enter. The math package method math.sqrt() does the calculation on the number
entered by the user. This number is obtained using the
GetNumber function which opens a dialog to request
the value. The square root of the returned value is assigned to
n. In the C and C++ languages, we would
think of n as being a "variable" which
must be declared at or before it is first used. In Lua, it is also
a variable but is created by being assigned a value (number,
string, etc.). In this casen becomes a
number (actually, a double precision floating point value). The
next statement, does some computations using n and assigns the result to a new
variable,f. The following statement
then defines a string by assigning a string value tos.
Next, the script calls the
CTextView class method
Printf to print the results. This function sends
C-style formatted text to a Mira text window. The format string
might be very simple or very complex (we have made it somewhere in
between). If you have a simple need to send text to a text window,
you could forget about using CTextView and, instead, use the global
Printf method to accomplish something similar.
Finally, since the script is finished using
T, the method T:
delete is called to free the CTextView object
from memory. If you forget to delete the object, Mira will do it
for you. However, it is a good practice to get used to doing it
explicitly, as it may be important in more complicated scripts.
Same Script Without the CTextView Class
The simple script above does not require the
CTextView class to accomplish the same thing.
When you simply want to send results to some Text Editor window,
you can simplify things. In this case, we can remove 3 lines from
the script and use the global
Printf function. The following script will give
exactly the same results as above:
n = math.sqrt( GetNumber(100)
)
-- get a number from the user, default to
100
f = n + math.log( n/55.4 )
-- do some math
s = "My String" .. " goes
here."
-- concatenate two strings
Printf("Val=%.2f\r\nStr= '%s'\r\n", f,s)
-- format f and s to the Text Editor.
In Summary
As you can see, the script syntax is in some ways
very much like the C and C++ languages. In fact, Lua has greatly
simplified the syntax of C and C++ to deliver a similar result. For
example, a Lua script creates a string simply by assigning a string
expression to a value. In particular, you might note the lack of
the C-style ; character at the end of each
statement. In Lua, the ;
delimiter is optional and you can use it according to your own
programming style. It may be useful as a separator when you place
multiple statements on the same line, as in w=I:Cols() ; h=I:Rows(),
but even in this case, Lua parses the line as containing 2
statements, and the; separator
is merely useful to help make the script easier for you to
read.
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