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89b93576
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Leszek Koltunski
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///////////////////////////////////////////////////////////////////////////////////////////////////
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// Copyright 2018 Leszek Koltunski //
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// //
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// This file is part of Distorted. //
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// //
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// Distorted is free software: you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation, either version 2 of the License, or //
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// (at your option) any later version. //
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// //
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// Distorted is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with Distorted. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////////////////////
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package org.distorted.library.mesh;
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///////////////////////////////////////////////////////////////////////////////////////////////////
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/**
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* Create a Mesh which approximates a sphere.
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* <p>
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* Do so by dividing each of the 20 faces of the regular icosahedron into smaller triangles and inflating
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* those to lay on the surface of the sphere.
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*/
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public class MeshSphere extends MeshBase
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{
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private static final int NUMFACES = 20;
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private static final double sqrt2 = Math.sqrt(2.0);
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private static final double P = Math.PI;
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private static final double A = 0.463647609; // arctan(0.5), +-latitude of the 10 'middle' vertices
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// https://en.wikipedia.org/wiki/Regular_icosahedron
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// An array of 20 entries, each describing a single face of the regular icosahedron in an (admittedly)
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// weird fashion.
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// Each face of a regular icosahedron is a equilateral triangle, with 2 vertices on the same latitude.
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// Single row is (longitude of V1, longitude of V2, (common) latitude of V1 and V2, latitude of V3)
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// longitude of V3 is simply midpoint of V1 and V2 so we don't have to specify it here.
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private static final double FACES[][] = {
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{ 0.0 , 0.4*P, A, 0.5*P },
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{ 0.4*P, 0.8*P, A, 0.5*P },
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{ 0.8*P, 1.2*P, A, 0.5*P }, // 5 'top' faces with
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{ 1.2*P, 1.6*P, A, 0.5*P }, // the North Pole
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{ 1.6*P, 2.0*P, A, 0.5*P },
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{ 0.0 , 0.4*P, A, -A },
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{ 0.4*P, 0.8*P, A, -A },
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{ 0.8*P, 1.2*P, A, -A }, // 5 faces mostly above
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{ 1.2*P, 1.6*P, A, -A }, // the equator
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{ 1.6*P, 2.0*P, A, -A },
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{ 0.2 , 0.6*P, -A, A },
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{ 0.6*P, 1.0*P, -A, A },
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{ 1.0*P, 1.4*P, -A, A }, // 5 faces mostly below
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{ 1.4*P, 1.8*P, -A, A }, // the equator
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{ 1.8*P, 0.2*P, -A, A },
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{ 0.2 , 0.6*P, -A,-0.5*P },
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{ 0.6*P, 1.0*P, -A,-0.5*P },
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{ 1.0*P, 1.4*P, -A,-0.5*P }, // 5 'bottom' faces with
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{ 1.4*P, 1.8*P, -A,-0.5*P }, // the South Pole
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{ 1.8*P, 0.2*P, -A,-0.5*P }
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};
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private int currentVert;
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private int numVertices;
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///////////////////////////////////////////////////////////////////////////////////////////////////
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// Each of the 20 faces of the icosahedron requires (level*level + 4*level) vertices for the face
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// itself and a join to the next face (which requires 2 vertices). We don't need the join in case
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// of the last, 20th face, thus the -2.
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// (level*level +4*level) because there are level*level little triangles, each requiring new vertex,
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// plus 2 extra vertices to start off a row and 2 to move to the next row (or the next face in case
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// of the last row) and there are 'level' rows.
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private void computeNumberOfVertices(int level)
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{
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numVertices = 20*level*(level+4) -2;
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currentVert = 0;
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}
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///////////////////////////////////////////////////////////////////////////////////////////////////
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// (longitude,latitude) - spherical coordinates of a point on a unit sphere.
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// Cartesian (0,0,1) - i.e. the point of the sphere closest to the camera - is spherical (0,0).
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private void addVertex( double longitude, double latitude, float[] attribs)
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{
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double sinLON = Math.sin(longitude);
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double cosLON = Math.cos(longitude);
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double sinLAT = Math.sin(latitude);
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double cosLAT = Math.cos(latitude);
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float x = (float)(cosLAT*sinLON / sqrt2);
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float y = (float)(sinLAT / sqrt2);
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float z = (float)(cosLAT*cosLON / sqrt2);
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attribs[VERT_ATTRIBS*currentVert + POS_ATTRIB ] = x; //
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attribs[VERT_ATTRIBS*currentVert + POS_ATTRIB+1] = y; //
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attribs[VERT_ATTRIBS*currentVert + POS_ATTRIB+2] = z; //
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// In case of this Mesh so it happens that
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attribs[VERT_ATTRIBS*currentVert + NOR_ATTRIB ] = x; // the vertex coords, normal vector, and
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attribs[VERT_ATTRIBS*currentVert + NOR_ATTRIB+1] = y; // inflate vector have identical (x,y,z).
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attribs[VERT_ATTRIBS*currentVert + NOR_ATTRIB+2] = z; //
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// TODO: think about some more efficient
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attribs[VERT_ATTRIBS*currentVert + INF_ATTRIB ] = x; // representation.
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attribs[VERT_ATTRIBS*currentVert + INF_ATTRIB+1] = y; //
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attribs[VERT_ATTRIBS*currentVert + INF_ATTRIB+2] = z; //
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attribs[VERT_ATTRIBS*currentVert + TEX_ATTRIB ] = (float)longitude;
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attribs[VERT_ATTRIBS*currentVert + TEX_ATTRIB+1] = (float)latitude;
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currentVert++;
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}
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///////////////////////////////////////////////////////////////////////////////////////////////////
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private void repeatLast(float[] attribs)
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{
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if( currentVert>0 )
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{
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attribs[VERT_ATTRIBS*currentVert + POS_ATTRIB ] = attribs[VERT_ATTRIBS*(currentVert-1) + POS_ATTRIB ];
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attribs[VERT_ATTRIBS*currentVert + POS_ATTRIB+1] = attribs[VERT_ATTRIBS*(currentVert-1) + POS_ATTRIB+1];
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attribs[VERT_ATTRIBS*currentVert + POS_ATTRIB+2] = attribs[VERT_ATTRIBS*(currentVert-1) + POS_ATTRIB+2];
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attribs[VERT_ATTRIBS*currentVert + NOR_ATTRIB ] = attribs[VERT_ATTRIBS*(currentVert-1) + NOR_ATTRIB ];
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attribs[VERT_ATTRIBS*currentVert + NOR_ATTRIB+1] = attribs[VERT_ATTRIBS*(currentVert-1) + NOR_ATTRIB+1];
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attribs[VERT_ATTRIBS*currentVert + NOR_ATTRIB+2] = attribs[VERT_ATTRIBS*(currentVert-1) + NOR_ATTRIB+2];
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attribs[VERT_ATTRIBS*currentVert + INF_ATTRIB ] = attribs[VERT_ATTRIBS*(currentVert-1) + INF_ATTRIB ];
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attribs[VERT_ATTRIBS*currentVert + INF_ATTRIB+1] = attribs[VERT_ATTRIBS*(currentVert-1) + INF_ATTRIB+1];
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attribs[VERT_ATTRIBS*currentVert + INF_ATTRIB+2] = attribs[VERT_ATTRIBS*(currentVert-1) + INF_ATTRIB+2];
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attribs[VERT_ATTRIBS*currentVert + TEX_ATTRIB ] = attribs[VERT_ATTRIBS*(currentVert-1) + TEX_ATTRIB ];
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attribs[VERT_ATTRIBS*currentVert + TEX_ATTRIB+1] = attribs[VERT_ATTRIBS*(currentVert-1) + TEX_ATTRIB+1];
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currentVert++;
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}
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}
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///////////////////////////////////////////////////////////////////////////////////////////////////
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// Supposed to return the latitude of the point between two points on the sphere with latitudes
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// lat1 and lat2, so if for example quot=0.2, then it will return the latitude of something 20%
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// along the way from lat1 to lat2.
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//
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// This is approximation only - in general it is of course not true that the midpoint of two points
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// on a unit sphere with spherical coords (A1,B1) and (A2,B2) is ( (A1+A2)/2, (B1+B2)/2 ) - take
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// (0,0) and (PI, epsilon) as a counterexample.
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//
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// Here however, the latitudes we are interested at are the latitudes of the vertices of a regular
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// icosahedron - i.e. +=A and +=PI/2, whose longitudes are close, and we don't really care if the
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// split into smaller triangles is exact.
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//
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// quot better be between 0.0 and 1.0.
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// this is 'directed' i.e. from lat1 to lat2.
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private double midLatitude(double lat1, double lat2, double quot)
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{
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return lat1*(1.0-quot)+lat2*quot;
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}
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///////////////////////////////////////////////////////////////////////////////////////////////////
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// Same in case of longitude. This is for our needs exact, because we are ever only calling this with
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// two longitudes of two vertices with the same latitude. Additional problem: things can wrap around
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// the circle.
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// this is 'undirected' i.e. we don't assume from lon1 to lon2 - just along the smaller arc joining
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// lon1 to lon2.
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private double midLongitude(double lon1, double lon2, double quot)
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{
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double min, max;
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if( lon1<lon2 ) { min=lon1; max=lon2; }
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else { min=lon2; max=lon1; }
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double diff = max-min;
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if( diff>P ) { diff=2*P-diff; min=max; }
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double ret = min+quot*diff;
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if( ret>=2*P ) ret-=2*P;
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return ret;
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}
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///////////////////////////////////////////////////////////////////////////////////////////////////
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// linear map (column,row, level):
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//
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// ( 0, 0, level) -> (lonV1,latV12)
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// ( 0, level-1, level) -> (lonV3,latV3 )
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// (level-1, 0, level) -> (lonV2,latV12)
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private void newVertex(float[] attribs, int column, int row, int level,
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double lonV1, double lonV2, double latV12, double latV3)
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{
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double quotX = (double)column/(level-1);
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double quotY = (double)row /(level-1);
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double lonPoint = midLongitude(lonV1,lonV2, (quotX+0.5*quotY) );
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double latPoint = midLatitude(latV12,latV3, quotY);
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addVertex(lonPoint,latPoint,attribs);
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}
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///////////////////////////////////////////////////////////////////////////////////////////////////
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private void buildFace(float[] attribs, int level, int face, double lonV1, double lonV2, double latV12, double latV3)
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{
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for(int row=0; row<level; row++)
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{
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for (int column=0; column<level-row; column++)
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{
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newVertex(attribs, column, row , level, lonV1, lonV2, latV12, latV3);
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if (column==0 && !(face==0 && row==0 ) ) repeatLast(attribs);
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newVertex(attribs, column, row+1, level, lonV1, lonV2, latV12, latV3);
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}
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newVertex(attribs, level-row, row , level, lonV1, lonV2, latV12, latV3);
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if( row!=level-1 || face!=NUMFACES-1 ) repeatLast(attribs);
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}
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}
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///////////////////////////////////////////////////////////////////////////////////////////////////
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// PUBLIC API
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///////////////////////////////////////////////////////////////////////////////////////////////////
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/**
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* Creates the underlying grid of vertices with the usual attribs which approximates a sphere.
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* <p>
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* When level=1, it outputs the 12 vertices of a regular icosahedron.
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* When level=N, it divides each of the 20 icosaherdon's triangular faces into N^2 smaller triangles
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* (by dividing each side into N equal segments) and 'inflates' the internal vertices so that they
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* touch the sphere.
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*
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* @param level Specifies the approximation level. Valid values: level ≥ 1
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*/
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public MeshSphere(int level)
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{
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super(1.0f);
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computeNumberOfVertices(level);
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float[] attribs= new float[VERT_ATTRIBS*numVertices];
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for(int face=0; face<NUMFACES; face++ )
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{
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buildFace(attribs, level, face, FACES[face][0], FACES[face][1], FACES[face][2], FACES[face][3]);
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}
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if( currentVert!=numVertices )
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android.util.Log.d("MeshSphere", "currentVert= " +currentVert+" numVertices="+numVertices );
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setAttribs(attribs);
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}
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}
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