C-language implementation of dot in polygon algorithm

This paper uses the Ray method to determine whether the point is within the Polygon C language program. Years ago, I realized such an algorithm myself. But over time, I decided to rewrite the code. Referring to Zhou Peide's "computational Geometry", combined with my practice and experience, I believe that this is the optimal code you have encountered so far in the implementation of this algorithm.

This is a C-language small algorithm implementation program, would not want to put here. However, when I want to implement such an algorithm, want to find a ready-made on the Internet, the study came down unexpectedly a meet the needs of the. I had no confidence in the code I wrote when I was a college student, so I decided to write a new one and put it here, readers. Also increase the number of clicks Blog.

First, define the point structure as follows:

以下是引用片段：
/* Vertex structure */
typedef struct
{
double x, y;
} vertex_t;

The polygon referred to in this algorithm refers to a closed simple polygon composed of a series of point sequences. Its end point can be or not the same point (not forcing the end point is the same point). Such a polygon can be of any shape, including multiple edges on an absolute line. Therefore, the definition of the polygon structure is as follows:

以下是引用片段：
/* Vertex list structure – polygon */
typedef struct
{
int num_vertices; /* Number of vertices in list */
vertex_t *vertex; /* Vertex array pointer */
} vertexlist_t;

In order to speed up the discriminant speed, first compute the bounding rectangle (rect_t) of the polygon, judge whether the point falls in the outer package rectangle, only the point that satisfies the condition in the outer package rectangle, then enters the next calculation. For this reason, the method of outsourcing rectangular structure rect_t and the outsourcing rectangle of the point collection is introduced Vertices_get_extent, the code is as follows:

以下是引用片段：
/* bounding rectangle type */
typedef struct
{
double min_x, min_y, max_x, max_y;
} rect_t;
/* gets extent of vertices */
void vertices_get_extent (const vertex_t* vl, int np, /* in vertices */
rect_t* rc /* out extent*/ )
{
int i;
if (np > 0){
rc->min_x = rc->max_x = vl[0].x; rc->min_y = rc->max_y = vl[0].y;
}else{
rc->min_x = rc->min_y = rc->max_x = rc->max_y = 0; /* =0 ? no vertices at all */
}
for(i=1; i
{
if(vl[i].x < rc->min_x) rc->min_x = vl[i].x;
if(vl[i].y < rc->min_y) rc->min_y = vl[i].y;
if(vl[i].x > rc->max_x) rc->max_x = vl[i].x;
if(vl[i].y > rc->max_y) rc->max_y = vl[i].y;
}
}