Channel Mod Linear Blend

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Channel Mod Linear Blend 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.

When installed, this plugin adds the Linear Blend channel modifier, which allows you to take two channel inputs and combine them into a single output.

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 CLxLuxologyLogMessage, 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 CLinearBlendInstance class so it writes out to the log when the server dependent on it is used.

class CLinearBlendLog : public CLxLuxologyLogMessage
       CLinearBlendLog () : CLxLuxologyLogMessage ("cmLinearBlend") { }

       const char *	 GetFormat  () { return "Linear Blend Object"; }

To create an instance of the Linear Blend object we need to implement the Linear Blend Package 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 CLinearBlendLog 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 linearly blend them.

class CLinearBlendInstance
       public CLxImpl_PackageInstance,
       public CLxImpl_ChannelModItem
       CLinearBlendLog		 log;
       CLinearBlendPackage	*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 CLinearBlendPackage : public CLxImpl_Package
       static LXtTagInfoDesc			descInfo[];
       CLxPolymorph<CLinearBlendInstance>	chanmod_factory;
       CLinearBlendPackage ();

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

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 CLinearBlendPackage class is dependent on the chanmodify SuperType with the internal name of cmLinearBlend.

LXtTagInfoDesc	 CLinearBlendPackage::descInfo[] = {
       { LXsPKG_SUPERTYPE,	"chanModify"	},
       { LXsSRV_LOGSUBSYSTEM,	"cmLinearBlend"	},
       { 0 }


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 CSimpleKinematicsPackage class that uses the Package and StaticDesc interfaces as well as being names cmSimpleKinematics.

initialize ()
       CLxGenericPolymorph		*srv;

       srv = new CLxPolymorph<CLinearBlendPackage>;
       srv->AddInterface (new CLxIfc_Package          <CLinearBlendPackage>);
       srv->AddInterface (new CLxIfc_StaticDesc       <CLinearBlendPackage>);
       thisModule.AddServer ("cmLinearBlend", srv);


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

CLinearBlendInstance::cmod_Evaluate (
       ILxUnknownID		 cmod,		// ILxChannelModifierID
       ILxUnknownID		 attr,		// ILxAttributesID
       void			*data)		

We create factories here to export CLinearBlendInstance.

CLinearBlendPackage::CLinearBlendPackage ()