Softimage Blog

var HISTOGRAM_RES = 256;
var INV_HISTOGRAM_RES = 0.00390625;
var HISTOGRAM_ARRSIZE = 257;
 
function OnEveryFrame(inParticleCloud, inTriggerParticleIndices, inSimFrame)
{
//Frame 99 is when the distribution will be viewed, and
//you can change it to whatever you want.
 
//Note that if you persist the histogram data objects, there's no
//reason you can't gather distributions across multiple frames.
 
//To make things a little easier to adjust, you may also want to
//create a custom property in the scene to tie this frame value to.
 
if(inSimFrame==99)
{
//Initialise the data
var histx = new HistogramData();
var histy = new HistogramData();
var histz = new HistogramData();
var histage = new HistogramData();
 
//This is where we store the data whose distribution we want to look at.
//In this case, we're observing position and age.
 
var particles = inParticleCloud.particles;
var num_particles = particles.count;
for(var i=0;i<num_particles;++i)
{
var particle = particles(i);
histx.ProcessSample(particle.position.x);
histy.ProcessSample(particle.position.y);
histz.ProcessSample(particle.position.z);
histage.ProcessSample(particle.age);
}
 
//Display the data
var histWindow = new ActiveXObject("HistogramDisplay.Application");
histWindow.SetHistogram(histx.curHist,"Pos.X", 0, histx.min, histx.max);
histWindow.SetHistogram(histy.curHist,"Pos.Y", 1, histy.min, histy.max);
histWindow.SetHistogram(histz.curHist,"Pos.Z", 2, histz.min, histz.max);
histWindow.SetHistogram(histage.curHist,"Age", 3, histage.min, histage.max);
 
histWindow.SetHistogramColor(0, 80, 0, 0);
histWindow.SetHistogramColor(1, 0, 80, 0);
histWindow.SetHistogramColor(2, 0, 0, 80);
histWindow.SetHistogramColor(3, 0, 0, 0);
 
histWindow.SetNumToDisplay(4);
histWindow.UpdateWindow();
}
}
 
//Data object representing histogram data
//and contains member function called ProcessSample()
 
function HistogramData()
{
this.min=0;
this.max=0;
this.samples=0;
 
this.curHist = new Array(HISTOGRAM_ARRSIZE);
this.otherHist = new Array(HISTOGRAM_ARRSIZE);
 
for(var i=0;i<HISTOGRAM_ARRSIZE;++i)
{
this.curHist[i]=0;
this.otherHist[i]=0;
}
 
this.ProcessSample = function(sample)
{
//This function does all the hard work
 
//It is a direct port from C++ of the functionality
//of the original Histogram rendertree shader
 
var oldMin = this.min;
var oldMax = this.max;
var oldBucketSize = (oldMax-oldMin)*INV_HISTOGRAM_RES;
 
var scaleChanged=false;
 
if(this.samples==0)
{
this.min = sample;
this.max = sample;
this.samples++;
return;
}
 
if(sample<this.min)
{
this.min = sample;
scaleChanged=true;
}
else if(sample>this.max)
{
this.max = sample;
scaleChanged=true;
}
 
if(this.samples==1)
{
this.curHist[0]++;
this.curHist[HISTOGRAM_RES]++;
this.samples++;
return;
}
 
var bucketSize = (this.max-this.min)*INV_HISTOGRAM_RES;
 
var rangeRatio = HISTOGRAM_RES/(this.max-this.min);
if((this.max-this.min)==0) rangeRatio=0;
 
if(scaleChanged)
{
//Swap histograms
var tempHist;
tempHist = this.curHist;
this.curHist = this.otherHist;
this.otherHist = tempHist;
 
//Copy and rescale the histogram according to the new sample and resample
for(var i=0;i<HISTOGRAM_ARRSIZE;i++)
{
//Calculate sample value
var value = oldMin + oldBucketSize*i;
 
//Calculate new bucket
var newBucket = Math.floor((value - this.min)*rangeRatio);
 
if(newBucket<0) newBucket=0;
if(newBucket>=HISTOGRAM_ARRSIZE) newBucket=HISTOGRAM_ARRSIZE-1;
 
this.curHist[newBucket]+=this.otherHist[i];
this.otherHist[i]=0;
}
}
 
//Add sample
var inputBucket = Math.floor((sample - this.min)*rangeRatio);
if(inputBucket<0) inputBucket=0;
if(inputBucket>=HISTOGRAM_ARRSIZE) inputBucket=HISTOGRAM_ARRSIZE-1;
this.curHist[inputBucket]++;
 
this.samples++;
}
}