10.4. Addition: Shifting the Whole Tip

10.4. Addition: Shifting the Whole Tip
	Chapter 10. Developing a Macro Module for an Applicator

In the example above, the change in length will be translated into an overall change with the center of rotation as overall center. However, it might be preferable to keep the tip in place and change the length of the shaft into the other direction.

Basically, this is the same problem as in the length calculation we made in the Python script. However, instead of calculating it in the macro scripting, we can also use a module for the calculation.

For this, the following modules need to be added:

SoCalculator: For calculating the length of the shaft.
SoComposeVec3f: For applying the translation of the float value to the vector of the overall translation in TranslationApplicator.

The SoCalculator module offers input and output of floating values and vectors.

Figure 10.18. Feeding the SoCalculator Module

Some important points:

In the Expression field, mathematic formulas can be entered; the name of the input values and the name of the output have to be given.
More than one expression can be entered. For that, end each line with a semicolon ;
For the expression to be calculated, you need to click Apply.

For calculating the translation from the input values of cone and shaft height, use the SoCalculator module and set up parameter connections

Connect SoCylinder.height to SoCalculator.a
Connect SoCone.height to SoCalculator.b
Enter the calculation: oa = - (0.5*a+0.5*b) (a negative sign needs to be added; otherwise, the end of the applicator is fixed and the tip side grows).

To apply the new translation, we need another SoComposeVec3f module. It allows for converting the float value y into a vector translation in y direction. For this, it needs to receive the output of SoCalculator and deliver the input for the SoTranslation module.

Connect SoCalculator.oa to SoComposeVec3f1.y
Connect SoComposeVec3f1.vector to SoTranslation.translation

	Tip
	You can find the names of the connected parameters by right-clicking the parameter connections. For an overview of all parameter connections in a network, use the Parameter Connections Inspector View.

The resulting macro network looks as follows:

Figure 10.19. Improved Applicator Macro Module

When to choose calculating values in scripts and when via modules? This is not an easy question.

The advantage of the script is that it is easily changed and extended. This might be harder with modules.
The main advantage of using script is that the setting of parameter field values or the triggering of a (re-)computation is much more controlled. Using parameter field connections can easily lead to unwanted notification avalanches.
The advantage of the modules is that the connections between modules are visible as parameter connections (which can be changed and removed).

In the end, it comes down to your current network and your design decisions which way to choose. Or you might combine them, like we did in our ApplicatorMacro network.

What else could you do now? You could, for example, make sure that the shaft length cannot be shorter than the tip length (which looks strange in the Open Inventor scene). You could also make the colors parametrizable, or add new features for the applicator.

This is the end of this example.

	Tip
	This example is delivered with MeVisLab (`.def` file in `$(InstallDir)Packages/MeVisLab/Examples/Modules/GettingStarted/ApplicatorMacroExample`, source files in `$(InstallDir)Packages/MeVisLab/Examples/Sources/GettingStarted/ApplicatorMacroExample`). The module can be added via quick search.


10.3. Programming the Python Script		Chapter 11. GUI Design in MeVisLab