Entering Data

Sometimes you might need the user to type a value or text in the Listener—an object name, a function value, a position, and so on. MAXScript provides functions for these types of tasks.

Entering Text

Using the GETKBLINE command you can ask the user to type text in the Listener. It may or not use a prompt to ask the user to type something. For example, you can use

user_name = getkbline prompt:”Enter your name:”

The user name will be stored in the user_name variable.

Entering Values

Using the GETKBVALUE command you can ask the user to type a numerical value in the Listener. It works exactly the same way as GETKBLINE, except that it returns a float or an integer variable.

	TIP Both GETKBVALUE and GETKBLINE can be used to ask the user to enter numeric values, but when using GETKBLINE, the script must convert the variable to float or integer, using variable = variable as float or as integer. If the user entered a letter instead of a number, the conversion will return undefined.

Using Conditions

Conditions are essential for any programming language. They allow you to test values and perform different actions, based on the result. Conditions make the script “think” and react the way you want it to.

If...

The IF command is very powerful. It can test and check for values and perform the selected actions if the comparison is met.

Comparing Variables

First, you need to learn how comparisons work in MAXScript. You can check for basically four conditions: whether two variables are equal or different, or whether one is greater or smaller than the other. This is done through a simple syntax: variable1 operation variable2. This expression will return true if the comparison is true, or false if it fails.

If a comparison is entered in the Listener, MAXScript will output true or false. If it’s part of a command, no value will be printed, but the command will read the true/false and will act as needed.

These are the comparisons that can be made in MAXScript:

Equal to and different from can be used in all variable types or functions. The remaining comparisons can be used only with numerical values or functions.

Actions Based on Comparisons

Using the IF command and comparisons, you can make the script react the way you want it to. We will use a simple example here to illustrate how conditions work, but you will see that we use conditions in all scripts we write, like checking whether the user selected a valid object, if the object has a material applied, if the value is a valid color value (color values must be in the range 0–255), etc. The next few chapters are full of practical examples of conditions and comparisons.

In this example you can check the current temperature to see whether it’s cold or hot. Then, if it’s cold, the script will output a sentence telling you it’s cold. If it’s hot, it can tell you it’s hot. This is a simple example of comparisons and actions based on comparisons.

The IF command requires two keywords to define which action to take: THEN and ELSE. It works by making a comparison; THEN, if the comparison is true, it runs a series of actions; ELSE, if the comparison is false, it runs a different set of actions. The ELSE statement can be omitted if a “false” result means the script just doesn’t do anything.

	NOTE The IF... THEN... command always waits for an ELSE to output all results. To see the result on screen after the latest IF, type something, and you’ll see the result being evaluated. Instead of IF... THEN... ELSE, you can use IF... DO, which will not wait for an ELSE; DO will evaluate the result automatically.

For instance, let’s write a small script to test whether the current temperature (30јF) is hot or cold:

cur_temperature = 30
if cur_temperature > 80 then print “It is hot.”
if cur_temperature < 40 then print “It is cold.”

In our example, the temperature will be checked, and the result will be output on the screen. If you want to go a bit further and allow the user to interact with the script, you can change the first line to

cur_temperature = getkbvalue prompt:”Enter current temperature:”

Now, the script works by itself and allows you to test for different temperature values.

Multiple Comparisons

Sometimes you might need to make more than one comparison. This can be done using Boolean expressions, such as AND and OR. The AND Boolean will return true only if all comparisons are true, and OR will return true if at least one returns true. For instance, (2 4) AND (sin 45 < 1) will return true, because both conditions are met. The expression (2 4) OR (sin 45 > 1) will also return true, because at least one of the conditions is true.

NOT is also a Boolean expression that will invert the expression being checked. For instance, NOT (2 > 4) will return true, because you’re checking to see if 2 is not greater than 4, which is true.

Using Boolean expressions makes it easier to create multiple comparisons, instead of creating a series of comparisons and commands. Let’s redo the temperature example, now using Boolean expressions and ELSE:

cur_temperature = getkbvalue prompt:”Enter current temperature:”
if (cur_temperature <= 80) AND (cur_temperature >= 40) then
 print “It is warm”
 else
 if cur_temperature > 80 then
 print “It is hot”
 else
 print “It is cold”

	TIP It’s useful to tabulate a script (that is, indent it with spaces or tabs like the example code above) so you can keep track of the organization of the comparisons. The MAXScript Editor makes it easy to create this formatting, inheriting the same tabulation when you break lines.

© 2000, Frol (selection, edition, publication)