Getting a NullPointerException at seemingly random intervals, not sure why
- by Miles
I'm running an example from a Kinect library for Processing (http://www.shiffman.net/2010/11/14/kinect-and-processing/) and sometimes get a NullPointerException pointing to this line:
int rawDepth = depth[offset];
The depth array is created in this line:
int[] depth = kinect.getRawDepth();
I'm not exactly sure what a NullPointerException is, and much googling hasn't really helped. It seems odd to me that the code compiles 70% of the time and returns the error unpredictably. Could the hardware itself be affecting it?
Here's the whole example if it helps:
// Daniel Shiffman
// Kinect Point Cloud example
// http://www.shiffman.net
// https://github.com/shiffman/libfreenect/tree/master/wrappers/java/processing
import org.openkinect.*;
import org.openkinect.processing.*;
// Kinect Library object
Kinect kinect;
float a = 0;
// Size of kinect image
int w = 640;
int h = 480;
// We'll use a lookup table so that we don't have to repeat the math over and over
float[] depthLookUp = new float[2048];
void setup() {
size(800,600,P3D);
kinect = new Kinect(this);
kinect.start();
kinect.enableDepth(true);
// We don't need the grayscale image in this example
// so this makes it more efficient
kinect.processDepthImage(false);
// Lookup table for all possible depth values (0 - 2047)
for (int i = 0; i < depthLookUp.length; i++) {
depthLookUp[i] = rawDepthToMeters(i);
}
}
void draw() {
background(0);
fill(255);
textMode(SCREEN);
text("Kinect FR: " + (int)kinect.getDepthFPS() + "\nProcessing FR: " + (int)frameRate,10,16);
// Get the raw depth as array of integers
int[] depth = kinect.getRawDepth();
// We're just going to calculate and draw every 4th pixel (equivalent of 160x120)
int skip = 4;
// Translate and rotate
translate(width/2,height/2,-50);
rotateY(a);
for(int x=0; x<w; x+=skip) {
for(int y=0; y<h; y+=skip) {
int offset = x+y*w;
// Convert kinect data to world xyz coordinate
int rawDepth = depth[offset];
PVector v = depthToWorld(x,y,rawDepth);
stroke(255);
pushMatrix();
// Scale up by 200
float factor = 200;
translate(v.x*factor,v.y*factor,factor-v.z*factor);
// Draw a point
point(0,0);
popMatrix();
}
}
// Rotate
a += 0.015f;
}
// These functions come from: http://graphics.stanford.edu/~mdfisher/Kinect.html
float rawDepthToMeters(int depthValue) {
if (depthValue < 2047) {
return (float)(1.0 / ((double)(depthValue) * -0.0030711016 + 3.3309495161));
}
return 0.0f;
}
PVector depthToWorld(int x, int y, int depthValue) {
final double fx_d = 1.0 / 5.9421434211923247e+02;
final double fy_d = 1.0 / 5.9104053696870778e+02;
final double cx_d = 3.3930780975300314e+02;
final double cy_d = 2.4273913761751615e+02;
PVector result = new PVector();
double depth = depthLookUp[depthValue];//rawDepthToMeters(depthValue);
result.x = (float)((x - cx_d) * depth * fx_d);
result.y = (float)((y - cy_d) * depth * fy_d);
result.z = (float)(depth);
return result;
}
void stop() {
kinect.quit();
super.stop();
}
And here are the errors:
processing.app.debug.RunnerException: NullPointerException
at processing.app.Sketch.placeException(Sketch.java:1543)
at processing.app.debug.Runner.findException(Runner.java:583)
at processing.app.debug.Runner.reportException(Runner.java:558)
at processing.app.debug.Runner.exception(Runner.java:498)
at processing.app.debug.EventThread.exceptionEvent(EventThread.java:367)
at processing.app.debug.EventThread.handleEvent(EventThread.java:255)
at processing.app.debug.EventThread.run(EventThread.java:89)
Exception in thread "Animation Thread" java.lang.NullPointerException
at org.openkinect.processing.Kinect.enableDepth(Kinect.java:70)
at PointCloud.setup(PointCloud.java:48)
at processing.core.PApplet.handleDraw(PApplet.java:1583)
at processing.core.PApplet.run(PApplet.java:1503)
at java.lang.Thread.run(Thread.java:637)
