Visibility
public class Visibility
extends Object
A collection of utility methods for computing the visibility of triangle meshes.
Summary
Public methods 
static void 
computeBoundingSphere(float[] positions, int positionsOffset, int positionsCount, float[] sphere, int sphereOffset) Compute a bounding sphere for a set of points. 
static int 
frustumCullSpheres(float[] mvp, int mvpOffset, float[] spheres, int spheresOffset, int spheresCount, int[] results, int resultsOffset, int resultsCapacity) Given an OpenGL ES ModelViewProjection matrix (which implicitly describes a frustum) and a list of spheres, determine which spheres intersect the frustum. 
static int 
visibilityTest(float[] ws, int wsOffset, float[] positions, int positionsOffset, char[] indices, int indicesOffset, int indexCount) Test whether a given triangle mesh is visible on the screen. 
Inherited methods 
From class java.lang.Object
Object 
clone() Creates and returns a copy of this object. 
boolean 
equals(Object obj) Indicates whether some other object is "equal to" this one. 
void 
finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. 
final Class<?> 
getClass() Returns the runtime class of this Object . 
int 
hashCode() Returns a hash code value for the object. 
final void 
notify() Wakes up a single thread that is waiting on this object's monitor. 
final void 
notifyAll() Wakes up all threads that are waiting on this object's monitor. 
String 
toString() Returns a string representation of the object. 
final void 
wait(long millis, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. 
final void 
wait(long millis) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed. 
final void 
wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object. 

Public constructors
Public methods
computeBoundingSphere
void computeBoundingSphere (float[] positions,
int positionsOffset,
int positionsCount,
float[] sphere,
int sphereOffset)
Compute a bounding sphere for a set of points. It is approximately the minimal bounding sphere of an axisaligned box that bounds the points.
Parameters 
positions 
float : positions in x, y, z triples 
positionsOffset 
int : offset into positions array 
positionsCount 
int : number of position triples to process 
sphere 
float : array containing the output as (x, y, z, r) 
sphereOffset 
int : offset where the sphere data will be written 
Throws 
IllegalArgumentException 
if positions is null, positionsOffset < 0, positionsOffset > positions.length  positionsCount, sphere is null, sphereOffset < 0, sphereOffset > sphere.length  4. 
frustumCullSpheres
int frustumCullSpheres (float[] mvp,
int mvpOffset,
float[] spheres,
int spheresOffset,
int spheresCount,
int[] results,
int resultsOffset,
int resultsCapacity)
Given an OpenGL ES ModelViewProjection matrix (which implicitly describes a frustum) and a list of spheres, determine which spheres intersect the frustum.
A ModelViewProjection matrix can be computed by multiplying the a Projection matrix by the a ModelView matrix (in that order.). There are several possible ways to obtain the current ModelView and Projection matrices. The most generally applicable way is to keep track of the current matrices in application code. If that is not convenient, there are two optional OpenGL ES extensions which may be used to read the current matrices from OpenGL ES:
 GL10Ext.glQueryMatrixxOES
 GL11.GL_MODELVIEW_MATRIX_FLOAT_AS_INT_BITS_OES and GL_PROJECTION_MATRIX_FLOAT_AS_INT_BITS_OES
The problem with reading back the matrices is that your application will only work with devices that support the extension(s) that it uses.
A frustum is a sixsided truncated pyramid that defines the portion of world space that is visible in the view.
Spheres are described as four floating point values: x, y, z, and r, in worldspace coordinates. R is the radius of the sphere.
Parameters 
mvp 
float : a float array containing the modeviewprojection matrix 
mvpOffset 
int : The offset of the mvp data within the mvp array. 
spheres 
float : a float array containing the sphere data. 
spheresOffset 
int : an offset into the sphere array where the sphere data starts 
spheresCount 
int : the number of spheres to cull. 
results 
int : an integer array containing the indices of the spheres that are either contained entirely within or intersect the frustum. 
resultsOffset 
int : an offset into the results array where the results start. 
resultsCapacity 
int : the number of array elements available for storing results. 
Returns 
int 
the number of spheres that intersected the frustum. Can be larger than resultsCapacity, in which case only the first resultsCapacity results are written into the results array. 
Throws 
IllegalArgumentException 
if mvp is null, mvpOffset < 0, mvpOffset > mvp.length  16, spheres is null, spheresOffset < 0, spheresOffset > spheres.length  sphereCount, results is null, resultsOffset < 0, resultsOffset > results.length  resultsCapacity. 
visibilityTest
int visibilityTest (float[] ws,
int wsOffset,
float[] positions,
int positionsOffset,
char[] indices,
int indicesOffset,
int indexCount)
Test whether a given triangle mesh is visible on the screen. The mesh is specified as an indexed triangle list.
Parameters 
ws 
float : the world space to screen space transform matrix, as an OpenGL column matrix. 
wsOffset 
int : an index into the ws array where the data starts. 
positions 
float : the vertex positions (x, y, z). 
positionsOffset 
int : the index in the positions array where the data starts. 
indices 
char : the indices of the triangle list. The indices are expressed as chars because they are unsigned 16bit values. 
indicesOffset 
int : the index in the indices array where the index data starts. 
indexCount 
int : the number of indices in use. Typically a multiple of three. If not a multiple of three, the remaining one or two indices will be ignored. 
Returns 
int 
2 if all of the mesh is visible, 1 if some part of the mesh is visible, 0 if no part is visible. 
Throws 
IllegalArgumentException 
if ws is null, wsOffset < 0, positions is null, positionsOffset < 0, indices is null, indicesOffset < 0, indicesOffset > indices.length  indexCount 