Channel Mod Linear Blend

From The Foundry MODO SDK wiki
Revision as of 17:57, 10 September 2013 by Adissid (Talk | contribs)

Jump to: navigation, search

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

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

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

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

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 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.

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);

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

Server Tags

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

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


initialize ()
       CLxGenericPolymorph		*srv;

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

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.


CLinearBlendInstance::cmod_Evaluate (
       ILxUnknownID		 cmod,		// ILxChannelModifierID
       ILxUnknownID		 attr,		// ILxAttributesID
       void			*data)		
       CLxLoc_ChannelModifier	 chanMod (cmod);
       double			 dValA, dValB, dVal, blend;
//	log.Info ("cmod_Evaluate Method");
       chanMod.ReadInputFloat (attr, 0, &dValA);
       chanMod.ReadInputFloat (attr, 1, &dValB);
       // Read the blend value and clamp between zero and one.
       chanMod.ReadInputFloat (attr, 2, &blend);
       if (blend < 0.0)
               blend = 0.0;
       else if (blend > 1.0)
               blend = 1.0;
       dVal = dValA + blend * (dValB - dValA);
       chanMod.WriteOutputFloat (attr, 0, dVal);
       return LXe_OK;

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

CLinearBlendPackage::CLinearBlendPackage ()
       chanmod_factory.AddInterface (new CLxIfc_PackageInstance<CLinearBlendInstance>);
       chanmod_factory.AddInterface (new CLxIfc_ChannelModItem<CLinearBlendInstance>);

We create factories here to export CLinearBlendInstance.