code: private double[] getAngles(double startAngle) {
          double[] angles = new double[_corners];
          angles[0] = startAngle;
          // 角度的增量
          double incremental = getAngleIncremental();
          for (int i = 1; i < _corners; i++) {
              angles[i] = angles[i - 1] + incremental;
          }
          return angles;
      }
docs: 获取各个顶点的角度列表