private void lightTriangle(int triIndex, float[] lightContribution) {
    int vIndex = triangles[triIndex][VERTEX1];
    copyVertexColor(triIndex, vIndex, 0, lightContribution);
    vIndex = triangles[triIndex][VERTEX2];
    copyVertexColor(triIndex, vIndex, 1, lightContribution);
    vIndex = triangles[triIndex][VERTEX3];
    copyVertexColor(triIndex, vIndex, 2, lightContribution);
  }