RifPlugin
No Translation Motion Blur

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Code

    RifPlugin NoTranslationBlur.cpp source code.

Introduction

This tutorial presents a simple RifPlugin that changes the way that motion blur is rendered. An object that is moving and rotating has one transform per motion sample. For example, the polycube shown in figure 1 is moving in the X direction and tumbling around the Z axis. In a RIB it's MotionBegin / MotionEnd might specify, for three motion samples, the following transforms.

Figure 1

MotionBegin [0 0.5 1]
    ConcatTransform [ 0.369 0.309 0 0  -0.309 0.369 -0 0  -0 0 0.482 0  0.015 0 0 1 ]
    ConcatTransform [ 0.293 0.382 0 0  -0.382 0.293 -0 0  -0 0 0.482 0  0.105 0 0 1 ]
    ConcatTransform [ 0.203 0.437 0 0  -0.437 0.203 -0 0  -0 0 0.482 0  0.194 0 0 1 ]
MotionEnd

The values hilited in red specify the X, Y and Z translations. The rif plugin reads the X,Y,Z values of the first transform and over-writes the corresponding values for the remaining transforms. For example,

MotionBegin [0 0.5 1]
    ConcatTransform [ 0.369 0.309 0 0  -0.309 0.369 -0 0  -0 0 0.482 0  0.015 0 0 1 ]
    ConcatTransform [ 0.293 0.382 0 0  -0.382 0.293 -0 0  -0 0 0.482 0  0.015 0 0 1 ]
    ConcatTransform [ 0.203 0.437 0 0  -0.437 0.203 -0 0  -0 0 0.482 0  0.015 0 0 1 ]
MotionEnd

The effect of "switching off" translation motion blur is shown below.

Figure 2 Rollover
Full motion blur and no translation motion blur

/*
Malcolm Kesson
March 9 2017
*/
#include <RifPlugin.h>
#include <RifFilter.h>
#include <ri.h>
#include <string>
#include <rx.h>
#include <sstream>
  
class NoTranslationBlur : public RifPlugin {
    public:
              NoTranslationBlur();
    virtual ~NoTranslationBlur() { }
    virtual RifFilter &GetFilter();
    
    private:
        RifFilter   m_filters;
        bool         m_motionBlockIsOpen;
        int         m_motionNumSamples;
        int         m_motionSample;
        RtFloat     m_xyz[3];
  
        // Callback_____________________________________________________________
        static RtVoid   motionBegin(int n, float times[]);
        static RtVoid   concatTransform(RtMatrix transform);
        static RtVoid   motionEnd();
    };
  
RifPlugin *RifPluginManufacture(int argc, char **argv) {
    return new NoTranslationBlur();
    }
        
NoTranslationBlur::NoTranslationBlur() {
    m_motionBlockIsOpen = false;
    m_motionNumSamples = 0;
    m_motionSample = 0;
    m_filters.MotionBeginV = motionBegin;
    m_filters.ConcatTransform = concatTransform;
    m_filters.MotionEnd = motionEnd;
    m_filters.Filtering = RifFilter::k_Continue;
    }
  
RifFilter& NoTranslationBlur::GetFilter() { 
    return m_filters; 
    }
    
RtVoid NoTranslationBlur::motionBegin(int n, float times[]) {
    NoTranslationBlur *self = static_cast<NoTranslationBlur*> (RifGetCurrentPlugin());
    self->m_motionNumSamples = n;
    self->m_motionBlockIsOpen = true;
    self->m_motionSample = 1;
    RiMotionBeginV(n, times);
    }
RtVoid NoTranslationBlur::concatTransform(RtMatrix transform) {
    NoTranslationBlur *self = static_cast<NoTranslationBlur*> (RifGetCurrentPlugin());
    if(self->m_motionBlockIsOpen == false) {
        RiConcatTransform(transform);
        return;
        }
    // Store the x,y,z values
    if(self->m_motionSample == 1) {
        self->m_xyz[0] = transform[3][0];
        self->m_xyz[1] = transform[3][1];
        self->m_xyz[2] = transform[3][2];
        //std::stringstream ss;
        //ss << transform[3][0];
        //RiArchiveRecord(RI_COMMENT, (char*)ss.str().c_str());
        self->m_motionSample += 1;
        }
    else
        {
        // Overwrite the x,y,z values
        transform[3][0] = self->m_xyz[0];
        transform[3][1] = self->m_xyz[1];
        transform[3][2] = self->m_xyz[2];
        }
    RiConcatTransform(transform);
    }
RtVoid NoTranslationBlur::motionEnd() {
    NoTranslationBlur *self = static_cast<NoTranslationBlur*> (RifGetCurrentPlugin());
    self->m_motionBlockIsOpen = false;
    self->m_motionNumSamples = 0;
    RiMotionEnd();
    }