Thoughts on Velocity Information

[RotemS]

Hi Vlado,

Thanks for that. The method seems to work correctly, though I still get almost identical artifacts. I can only deduce that I was wrong in my conclusion that mapToScreen was the only culprit. I now find it likely that DefaultVrayShadeInstance::getBasePt returning a single precision Vector is also to blame. This makes sense as the coordinates I'm testing with are in a range close to the accuracy limit of float.

I apologize for my misguided conclusion. If you ever get a chance to revise getBasePt please let me know.

For reference, below is my updated method

DefaultVRayShadeInstance *si = dynamic_cast<DefaultVRayShadeInstance*>GET_INTERFACE(rc.rayresult.si, EXT_DEFAULT_SHADE_INSTANCE);
if (si)
{
	// Get the world-coordinate point at the start of the motion blur interval
	Vector offsetPt = si->getBasePt(rc, (which == timeMoment_frameEnd) ? 
		DefaultVRayShadeInstance::baseTime_frameEnd : 
		DefaultVRayShadeInstance::baseTime_frameStart);

	// Project the point onto the camera at the start of the motion blur interval
	const VRaySequenceData &sdata = rc.vray->getSequenceData();
        	double time = (which == timeMoment_frameEnd) ? 1.0 : 0.0;
	        TracePoint offsetPtCam = sdata.cameraImageSampler->interpolateTimePointInverse(TracePoint(offsetPt), time);
	
	VR::Vector2 offset_p_img, this_p_img;

	if (sdata.cameraRaySampler->canDoDOF() & VR::vrayCameraFlags_canDoFrustrum) 
	{
		  Vector2 screenPt;
		  VRayCamera3* cam3 = static_cast<VRayCamera3*>(sdata.cameraRaySampler);
		  if (!cam3->mapTracePointToScreen(offsetPtCam, offset_p_img, time) ||
	              !cam3->mapTracePointToScreen(rc.rayresult.getPoint(), this_p_img, 0.5))
		  {
				  return Vector(0.0F);
		  }
	}
	else
	{
		if (!sdata.cameraRaySampler->mapToScreen(offsetPtCam, offset_p_img, time) ||
    		    !sdata.cameraRaySampler->mapToScreen(rc.rayresult.getPoint(), this_p_img, 0.5))
		{
			return Vector(0.0F);
		}
	}
	const VRayFrameData &fdata = rc.vray->getFrameData();
	TracePoint origCamPos = fdata.camToWorld.offs;
	TracePoint offsetCamPos = sdata.cameraImageSampler->interpolateTimePoint(origCamPos, time);

	const double thisDepth = rc.rayresult.wpointCoeff;
	const double offsetDepth = (offsetCamPos - offsetPt).length();
	double depthDelta =  thisDepth - offsetDepth;
	return Vector(
		(double)offset_p_img.x - (double)this_p_img.x,
		(double)offset_p_img.y - (double)this_p_img.y,
		depthDelta);
}
return Vector(0.0F);