Channel Mod Math Multi

Channel Mod Math Multi is a basic example plugin. This wiki page is intended as a walkthrough of the code in order to help you better understand the SDK.

This plugin is a channel modifier that takes in input and performs mathematical inputs on them. This is further explained in the functionality section below.

Functionality

Below, We have three cubes that the math multi is acting upon. The modifier is taking in one cube’s x-coordinate(3m) and the other’s y-coordinate(3m). The result is being exported to the z-coordinate of the cube in the middle

The untransformed cubes

Here, the two inputs are being added together

Here, the two inputs are being multiplied together

Here, the two inputs are being divided

The difference of the two inputs is being taken here.

Code Walkthrough

Class Declarations

The classes are structured in a nested format. We first declare a class to interact with the log. Following that we declare an object of that type in a class that creates an instance of our linear channel modifier. We then create a package class in which we attach the instance class.

The first class declaration inherits from FAQ#Q:_How_do_I_write_to_the_log.3F, which is the same as inheriting from ClxLogMessage but with an added Luxology copyright. Inside the class we have a CLinearBlendLog which defines what we will actually be writing out to the log. An object of this type is defined in our CMathMulti class so it writes out to the log when the server dependent on it is used.

We want to have this class write out to the log, so we inherit from CLxLuxologyLogMessage]].

 class CMathMultiLog : public CLxLuxologyLogMessage
 {
    public:
        CMathMultiLog () : CLxLuxologyLogMessage ("cmMathMulti") { }

        const char *     GetFormat  () { return "Math Multiple Object"; }
 };

To create an instance of the Math Multi object we need to implement the Math Multi object so we inherit from CLxPackageInstance. We also need to modify channels as part of our instance, so we inherit from CLxImpl_ChannelModItem.

Inside our class, we declare an object of the CMathMultiLog type, which is the class we just wrote above. Following that we have three functions with the pins prefix, which indicates that they are redeclarations of virtual functions declared in the CLxImplPackageInstance class. The initialize class adds the m_item object to our instance. Next, our Synthname function gives a name to the the instance. The Cleanup function shuts down our instance by releasing the m_item object from our instance.

The next four functions have cmod prefixes, indicating that they are redeclarations of virtual functions declared in the CLxImplChannelModItem class. Our Flags function looks at the state of the channel that the instance is currently dealing with and throws a flag indicating as to whether or not it is connected to input a, b, or the output. Our Allocate function then looks up and adds all the channels. The evaluate function then takes the values present in each of the input channels and performs the operation we want on them. In this case, it is to perform basic mathematical operations on them.

 class CMathMultiInstance
        :
        public CLxImpl_PackageInstance,
        public CLxImpl_ChannelModItem
 {
        CMathMultiLog            log;

    public:
        CMathMultiPackage       *src_pkg;
        CLxUser_Item             m_item;
        ILxUnknownID             inst_ifc;

        LxResult                 pins_Initialize (ILxUnknownID item, ILxUnknownID super);
        void                     pins_Cleanup (void);
        LxResult                 pins_SynthName (char *buf, unsigned len);

        unsigned int             cmod_Flags (ILxUnknownID item, unsigned int index);
        LxResult                 cmod_Allocate (
                                        ILxUnknownID cmod,
                                        ILxUnknownID eval,
                                        ILxUnknownID item,
                                        void **ppvData);
        void                     cmod_Cleanup (void *data);
        LxResult                 cmod_Evaluate (ILxUnknownID cmod, ILxUnknownID attr, void *data);
 };

To set up our object we need a package, so we have this class inherit from CLxImpl_Package.

We start off by declaring a factory which is a utility that allows server attributes to be read and new server instances to be spawned.

Following this, we have three functions with the pkg prefix, indicating that they are redeclarations of functions in the CLxImplPackage class. The first sets up some channels for our package, and the second sets up a test interface. The most important of the three, though, is our attach function. What this function does is create an object of the CLinearBlendInstance type using the factory that we declared and attach it to our package.

 class CMathMultiPackage : public CLxImpl_Package
 {
    public:
        static LXtTagInfoDesc            descInfo[];
        CLxPolymorph<CMathMultiInstance> chanmod_factory;

        CMathMultiPackage ();

        LxResult                pkg_SetupChannels (ILxUnknownID addChan);
        LxResult                pkg_TestInterface (const LXtGUID *guid);
        LxResult                pkg_Attach (void **ppvObj);
 };

:doc:`./Server_Tags `

Servers tags are examined when the server is initialized, and give information about the server. We set the tags in this case by taking descinfo[] arrays and associating the relevant data with the corresponding flags.

The tags here indicate that the CMathMultisPackage class is dependent on the chanmodify SuperType with the internal name of cmMathMulti.

 LXtTagInfoDesc  CMathMultiPackage::descInfo[] = {
        { LXsPKG_SUPERTYPE,     "chanModify"    },
        { LXsSRV_LOGSUBSYSTEM,  "cmMathMulti"   },
        { 0 }
 };

./Initialize_(index)

Intialize is called when we add the plugin to modo, and is the utility that exports the server.

Our initialize function indicates that we will be exporting one server dependent on the CMathMultiPackage class that uses the Package and StaticDesc interfaces as well as being names cmMathMulti.

        void
 initialize ()
 {
        CLxGenericPolymorph             *srv;

        srv = new CLxPolymorph<CMathMultiPackage>;
        srv->AddInterface (new CLxIfc_Package          <CMathMultiPackage>);
        srv->AddInterface (new CLxIfc_StaticDesc       <CMathMultiPackage>);
        thisModule.AddServer ("cmMathMulti", srv);
 }

Implementations

This function evaluates the modifiers we have used on the given channels.

        LxResult
CMathMultiInstance::cmod_Evaluate (
        ILxUnknownID             cmod,          // ILxChannelModifierID
        ILxUnknownID             attr,          // ILxAttributesID
        void                    *data)          // User Data
{
        ...
}

This function creates Factory_Object to export CMathMultiInstance.

 CMathMultiPackage::CMathMultiPackage ()
 {
        ...
 }