Java Random Int randomPointInConvexPoly(float[] pts, int npts, float[] areas, float s, float t)

Description

random Point In Convex Poly

License

Open Source License

Declaration

static float[] randomPointInConvexPoly(float[] pts, int npts,
            float[] areas, float s, float t) 

Method Source Code

//package com.java2s;

public class Main {
    static float[] randomPointInConvexPoly(float[] pts, int npts,
            float[] areas, float s, float t) {
        // Calc triangle araes
        float areasum = 0.0f;
        for (int i = 2; i < npts; i++) {
            areas[i] = triArea2D(pts, 0, (i - 1) * 3, i * 3);
            areasum += Math.max(0.001f, areas[i]);
        }//from  w ww .ja  v  a2 s .c  om
        // Find sub triangle weighted by area.
        float thr = s * areasum;
        float acc = 0.0f;
        float u = 0.0f;
        int tri = 0;
        for (int i = 2; i < npts; i++) {
            float dacc = areas[i];
            if (thr >= acc && thr < (acc + dacc)) {
                u = (thr - acc) / dacc;
                tri = i;
                break;
            }
            acc += dacc;
        }

        float v = (float) Math.sqrt(t);

        float a = 1 - v;
        float b = (1 - u) * v;
        float c = u * v;
        int pa = 0;
        int pb = (tri - 1) * 3;
        int pc = tri * 3;

        return new float[] { a * pts[pa] + b * pts[pb] + c * pts[pc],
                a * pts[pa + 1] + b * pts[pb + 1] + c * pts[pc + 1],
                a * pts[pa + 2] + b * pts[pb + 2] + c * pts[pc + 2] };
    }

    public static float triArea2D(float[] verts, int a, int b, int c) {
        float abx = verts[b] - verts[a];
        float abz = verts[b + 2] - verts[a + 2];
        float acx = verts[c] - verts[a];
        float acz = verts[c + 2] - verts[a + 2];
        return acx * abz - abx * acz;
    }

    public static float triArea2D(float[] a, float[] b, float[] c) {
        float abx = b[0] - a[0];
        float abz = b[2] - a[2];
        float acx = c[0] - a[0];
        float acz = c[2] - a[2];
        return acx * abz - abx * acz;
    }
}

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