测试两个矩形是否相交即相交区域算法

Andrew Huang

  在课堂实现的游戏碰撞算法需要使用矩形相交算法，因此按如下思路实现Pure C代码
 http://tonnypc.blog.163.com/blog/static/12258507920112222549172/

 

/*
  Author:Andrew Huang <[e-mail]>
    test rect interest .
 */
#include <stdio.h>

struct rect{
  int x;
  int y;
  int w;
  int h;
};

#define ARY_SIZE(a)  (sizeof(a)/sizeof(a[0]))

void test_rect(struct rect * ra,struct rect * rb);
void test_inter(struct rect * ra,struct rect * rb);

int main()
{
  int i;
  struct rect rects[] = {
    {0,0,10,10},{20,20,10,10} , /* 不相交 */
    {20,20,10,10},{0,0,10,10},  /* 不相交 */
    {0,0,10,10},{0,0,10,10} ,   /* 重合  */
    {30,30,10,10},{20,20,40,40} , /* 包含  */
    {30,30,40,40},{60,40,50,50} , /* 交错  */
    {30,30,40,40},{30,70,40,40} , /* 平行  */
    {30,30,40,40},{30,71,40,40} , /*   */
  };

   for(i=0 ; i<ARY_SIZE(rects)/2;i++)
   {
        test_rect(rects+(2*i),rects+(2*i+1));
        test_inter(rects+(2*i),rects+(2*i+1));
       printf("\n");
   }

  return 0;
}

int _abs(int val)
{
  return (val<0) ? -val : val;
}
/* 判断是否相交*/
int test_rect_cross(struct rect * ra,struct rect * rb)
{

  int a_cx,a_cy; /* 第一个中心点*/
  int b_cx,b_cy; /* 第二个中心点*/

  a_cx = ra->x + (ra->w/2);
  a_cy = ra->y + (ra->h/2);

  b_cx = rb->x + (rb->w/2);
  b_cy = rb->y + (rb->h/2);

  return (  (_abs(a_cx - b_cx) <= (ra->w/2 + rb->w/2))
     &&  (_abs(a_cy - b_cy) <= (ra->h/2 + rb->h/2)));
}

int _max(int a,int b)
{
  return a>b ? a : b;
}

int _min(int a,int b)
{
  return a<b ? a : b;
}


/* 求两个矩形相交矩形*/
int get_rect_inter(struct rect * ra,struct rect *  rb,
 struct  rect * result)
{
  int tl_x,tl_y;
  int br_x,br_y;

  tl_x = _max(ra->x,rb->x);
  tl_y = _max(ra->y,rb->y);

  br_x = _min(ra->x+ra->w,rb->x+rb->w);
  br_y = _min(ra->y+ra->h,rb->y+rb->h);

  if( (tl_x > br_x ) || (tl_y > br_y ) )
     return 0 ; /* 没有交集*/
  if(result)
  {
  result->x = tl_x ;
  result->y = tl_y ;
  result->w = br_x - tl_x ;
  result->h = br_y - tl_y ;
  }
  return 1;

}


void test_rect(struct rect * ra,struct rect * rb)
{
   printf("rect a= { %d,%d,%d,%d} \n",ra->x,ra->y,ra->w,ra->h);
   printf("rect b= { %d,%d,%d,%d} \n",rb->x,rb->y,rb->w,rb->h);

   printf("\ttest result %d\n",test_rect_cross(ra,rb));
}

void test_inter(struct rect * ra,struct rect * rb)
{

  struct rect result;

  if(get_rect_inter(ra,rb,&result))
   {
      printf("\t inter rect = {%d,%d,%d,%d}\n",
         result.x,result.y,result.w,result.h);
   }
 else
   {
       printf("\t no inter rect\n");
   }

}

测试结果如下
 

[blues@localhost test_rect]$ gcc main.c -o test_rect
[blues@localhost test_rect]$ ./test_rect
rect a= { 0,0,10,10}
rect b= { 20,20,10,10}
test result 0
no inter rect

rect a= { 20,20,10,10}
rect b= { 0,0,10,10}
test result 0
no inter rect

rect a= { 0,0,10,10}
rect b= { 0,0,10,10}
test result 1
inter rect = {0,0,10,10}

rect a= { 30,30,10,10}
rect b= { 20,20,40,40}
test result 1
inter rect = {30,30,10,10}

rect a= { 30,30,40,40}
rect b= { 60,40,50,50}
test result 1
inter rect = {60,40,10,30}

rect a= { 30,30,40,40}
rect b= { 30,70,40,40}
test result 1
inter rect = {30,70,40,0}

rect a= { 30,30,40,40}
rect b= { 30,71,40,40}
test result 0
no inter rect

[blues@localhost test_rect]$

 test_rect.zip