Filter Nodes - Arnold Developer Guide

Example

This is an example filter node plugin, equivalent to the built-in gaussian_filter.

custom_gaussian_filter.cpp

#include <ai.h>
#include <string.h>

AI_FILTER_NODE_EXPORT_METHODS(CustomGaussianFilterMtd);

struct FilterData
{
   float width;
};

node_parameters
{
   AiParameterFlt("width", 2.0f);
}

node_initialize
{
   AiFilterInitialize(node, false, NULL);
   AiNodeSetLocalData(node, new FilterData());
}

node_update
{
   FilterData* filter_data = (FilterData*)AiNodeGetLocalData(node);
   filter_data->width = AiNodeGetFlt(node, AtString("width"));
   AiFilterUpdate(node, filter_data->width);
}

node_finish
{
   FilterData* filter_data = (FilterData*)AiNodeGetLocalData(node);
   delete filter_data;
}

filter_output_type
{
   switch (input_type)
   {
      case AI_TYPE_RGBA:
         return AI_TYPE_RGBA;
      default:
         return AI_TYPE_NONE;
   }
}

filter_pixel
{
   FilterData* filter_data = (FilterData*)AiNodeGetLocalData(node);
   const float width = filter_data->width;

   float aweight = 0.0f;
   AtRGBA avalue = AI_RGBA_ZERO;

   while (AiAOVSampleIteratorGetNext(iterator))
   {
      // take into account adaptive sampling
      float inv_density = AiAOVSampleIteratorGetInvDensity(iterator);
      if (inv_density <= 0.f)
         continue;

      // determine distance to filter center
      const AtVector2& offset = AiAOVSampleIteratorGetOffset(iterator);
      const float r = AiSqr(2 / width) * (AiSqr(offset.x) + AiSqr(offset.y));
      if (r > 1.0f)
         continue;

      // gaussian filter weight
      const float weight = AiFastExp(2 * -r) * inv_density;

      // accumulate weights and colors
      avalue += weight * AiAOVSampleIteratorGetRGBA(iterator);
      aweight += weight;
   }

   // compute final filtered color
   if (aweight != 0.0f)
      avalue /= aweight;
   *((AtRGBA*)data_out) = avalue;
}

node_loader
{
   if (i>0)
      return false;

   node->methods      = CustomGaussianFilterMtd;
   node->output_type  = AI_TYPE_NONE;
   node->name         = "custom_gaussian_filter";
   node->node_type    = AI_NODE_FILTER;
   strcpy(node->version, AI_VERSION);
   return true;
} 

Example Scene

The following .ass file generates an image similar to the one at the top of this page

custom_gaussian_filter.ass

options
{
 AA_samples 1
 outputs "RGBA RGBA filter testrender"
}

custom_gaussian_filter
{
  name filter
  width 16
}

driver_jpeg
{
  name testrender
  filename testrender.jpg
  color_space sRGB
}

persp_camera
{
 name mycamera
 position 5 4 5
 look_at 0 0 0
 up 0 1 0
 fov 50
}

utility
{
 name myutil
 color_mode n
 shade_mode flat
}

sphere
{
 name mysphere
 center 0 0 0
 radius 2
 shader myutil
}