IllegalArgumentException from gluUnProject

Question

I get this error message

08-30 19:20:17.774: ERROR/AndroidRuntime(4681): FATAL EXCEPTION: GLThread 9
08-30 19:20:17.774: ERROR/AndroidRuntime(4681): java.lang.IllegalArgumentException: length - offset < n
08-30 19:20:17.774: ERROR/AndroidRuntime(4681):     at android.opengl.Matrix.multiplyMV(Native Method)
08-30 19:20:17.774: ERROR/AndroidRuntime(4681):     at android.opengl.GLU.gluUnProject(GLU.java:237)
08-30 19:20:17.774: ERROR/AndroidRuntime(4681):     at android.app.ui.GLSurfaceRenderer.vector3(GLSurfaceRenderer.java:70)
08-30 19:20:17.774: ERROR/AndroidRuntime(4681):     at android.app.ui.GLSurfaceRenderer.onDrawFrame(GLSurfaceRenderer.java:103)
08-30 19:20:17.774: ERROR/AndroidRuntime(4681):     at android.opengl.GLSurfaceView$GLThread.guardedRun(GLSurfaceView.java:1332)
08-30 19:20:17.774: ERROR/AndroidRuntime(4681):     at android.opengl.GLSurfaceView$GLThread.run(GLSurfaceView.java:1116)

With this code:

import android.opengl.GLU;
import android.opengl.GLSurfaceView.Renderer;
import android.util.*;


public class GLSurfaceRenderer implements Renderer{


public static float setx, sety;
private static float posx, posy, posz = 100;
private double speed;
private static float rotation;
private static float statrotation;
public static boolean isPressed;

private static FlatColoredSquare square;
private static FlatColoredSquare statSquare;
public final static String TAG = "input";






    public GLSurfaceRenderer () {

    square = new FlatColoredSquare();
    statSquare = new FlatColoredSquare();
    rotation = (float) Math.floor(Math.random()*361);
    speed = 0.1;




    }

    public void vector3 (GL11 gl){

        int[] viewport = new int[4];
        float[] modelview = new float[16];
        float[] projection = new float[16];
        float winx, winy, winz;
        float[] newcoords = new float[3];

        gl.glGetIntegerv(GL11.GL_VIEWPORT, viewport, 0);
        ((GL11) gl).glGetFloatv(GL11.GL_MODELVIEW_MATRIX, modelview, 0);
        ((GL11) gl).glGetFloatv(GL11.GL_PROJECTION_MATRIX, projection, 0);

        winx = (float)setx;
        winy = (float)viewport[3] - sety;
        winz = 0;

        GLU.gluUnProject(winx, winy, winz, modelview, 0, projection, 0,   viewport, 0, newcoords, 0);
        posx = (int)newcoords[1];
        posy = (int)newcoords[2];
        posz = (int)newcoords[3];



        Log.d(TAG, "vector3 Used");
    }


 @Override
public void onDrawFrame(GL10 gl) {
         gl.glClear(GL10.GL_COLOR_BUFFER_BIT |
            GL10.GL_DEPTH_BUFFER_BIT);
    gl.glLoadIdentity();
    gl.glScalef(100, 100, 0);
    gl.glPushMatrix();
    gl.glRotatef(rotation, 0, 0, 1);
    gl.glTranslatef((float) speed/10, 0, 0);    
    square.draw(gl);    
    gl.glPopMatrix();

    gl.glPushMatrix();
    gl.glTranslatef(posx, posy, posz);
    gl.glRotatef(statrotation,0,0,1);
    statSquare.draw(gl);
    gl.glPopMatrix();


    statrotation++;
    speed++;
    Log.d(TAG, "Frame Drawn");
    vector3((GL11) gl);

}   

@Override
public void onSurfaceChanged(GL10 gl, int width, int height) {
    gl.glViewport(0, 0, width, height);
    gl.glMatrixMode(GL10.GL_PROJECTION);
    gl.glLoadIdentity();
    GLU.gluOrtho2D(gl, -width, width, -height, height);
    gl.glMatrixMode(GL10.GL_MODELVIEW);
    gl.glLoadIdentity();


}




@Override
public void onSurfaceCreated(GL10 gl, EGLConfig config) {
    gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    gl.glShadeModel(GL10.GL_SMOOTH);
    gl.glClearDepthf(1.0f);
    gl.glEnable(GL10.GL_DEPTH_TEST);
    gl.glDepthFunc(GL10.GL_LEQUAL);
    gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST);

}






} 

Notice that I have attempted to call the vector3() method in my Draw method which appears to work because it reads far enough to pick out an error in the actual method. The error is thrown at this line

GLU.gluUnProject(winx, winy, winz, modelview, 0, projection, 0,   viewport, 0, newcoords, 0);

Note that setx and sety should be equal to 0 at the point the error is thrown as the screen has not yet been touched.

Could the error be anything to do with my glSurfaceView?

import android.content.Context;
import android.opengl.GLSurfaceView;
import android.util.*;
import android.view.MotionEvent;



public class Input extends GLSurfaceView {

public GLSurfaceRenderer glSurfaceRenderer;
public float setx, sety;
public final static String TAG = "input";


public Input(Context context) {
    super(context);


    glSurfaceRenderer = new GLSurfaceRenderer();
    setRenderer(glSurfaceRenderer);


}


@Override
public boolean onTouchEvent(MotionEvent event){
    if (event.getAction() == MotionEvent.ACTION_DOWN){
    setx = event.getX();
    sety = event.getY();


    Log.d(TAG, "isPressed triggered");
    }
    return true;
}

}

Answer 1

I've briefly looked at the source code for this function, and it appears to expect your newcoords vector to have size 4 instead of 3. They are homogeneous coordinates, so you will also have to divide by w to get your actual coordinates.

Note that there's another error in your code as well, you're indexing newcoords out of bounds after the call to gluUnProject. The first element is newcoords[0], not newcoords[1].

I think if you use something like this, it would work better (I didn't test this though):

float[] newcoords = new float[4]; // Note size 4!!
GLU.gluUnProject(...);
float x = newcoords[0] / newcoords[3];
float y = newcoords[1] / newcoords[3];
float z = newcoords[2] / newcoords[3];