Visibility

Visibility

Visibility ()

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 axis-aligned 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 ModelView-Projection matrix (which implicitly describes a frustum) and a list of spheres, determine which spheres intersect the frustum.

A ModelView-Projection 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 six-sided 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 world-space coordinates. R is the radius of the sphere.

Parameters
mvp	float: a float array containing the mode-view-projection 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 16-bit 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