游戏中判断一群点可否构成凸多边形
下面的代码需要box2d！！！！！！！！！！！
import org.jbox2d.common.Vec2;
public class PolyonUtil {
?private static PolyonUtil instance;
?private float a;
?private float b;
?private boolean x_axis;
?private boolean y_axis;
?private float axis;
?float i;
?public static PolyonUtil getInstance() {
??if (instance == null) {
???instance = new PolyonUtil();
??}
??return instance;
?}
?public void setAB(Vec2 point1, Vec2 point2) {
??if (point1.x == point2.x) {
???if (point1.y != point2.y) {
????y_axis = true;
????axis = point1.x;
???}
??} else if (point1.y == point2.y) {
???if (point1.x != point2.x) {
????x_axis = true;
????axis = point1.y;
???}
??} else {
???y_axis = false;
???x_axis = false;
???a = (point1.y - point2.y) / (point1.x - point2.x);
???b = point1.y - point1.x * a;
??}
?}
?public byte getFlag(Vec2 point) {
??if (y_axis) {
???if (point.x > axis) {
????return 1;
???} else if (point.x < axis) {
????return -1;
???} else {
????return 0;
???}
??} else if (x_axis) {
???if (point.y > axis) {
????return 1;
???} else if (point.y < axis) {
????return -1;
???} else {
????return 0;
???}
??} else {
??? i = point.y - a * point.x - b;
???if ((point.y - a * point.x - b) < 0) {
????return -1;
???} else if ((point.y - a * point.x - b) > 0) {
????return 1;
???} else {
????return 0;
???}
??}
?}
}
//下面的函数判断一群点是否构成凸多边形
public boolean isHull(Vec2[] mouseStroke){
int mouseStrokeLength=mouseStroke.length;
for (int i = 0; i < mouseStrokeLength; i+=2) {
???PolyonUtil.getInstance().setAB(mouseStroke[(i) % mouseStrokeLength],
?????mouseStroke[(i + 1) % mouseStrokeLength]);
???for (int j = 0, k = 0; j < mouseStrokeLength; j++) {
????if (j == i || j == (i + 1)) {
?????continue;
????} else {
?????flag[k] = PolyonUtil.getInstance().getFlag(mouseStroke[j
???????% mouseStrokeLength]);
?????k++;
????}
???}
???for (int l = 0; l < flag.length - 1; l++) {
????if (flag[l] * flag[l + 1] < 0) {
?????// ao 当是凹多边形时候
??????????return false;
????}
???}
??}
return true;
}
