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/*
* This file is subject to the terms of the GFX License. If a copy of
* the license was not distributed with this file, you can obtain one at:
*
* http://ugfx.io/license.html
*/
#include "../../gfx.h"
#if GFX_USE_GMISC
#if GMISC_NEED_HITTEST_POLY
/* This function is used by gmiscHittestPoly()
*
* This function projects the point c on an horizontal line to the right.
* If the projection cuts the segment formed by the points a and b,
* the function returns 1. If the point c is on the segment, the function
* returns 0. If they don't intersect, it returns 2.
*/
static char _pointCrossingSegment(const gPoint *a, const gPoint *b, const gPoint *c) {
/* If both points are left from our point, it won't intersect */
if (a->x < c->x && b->x < c->x) {
return -1;
}
/* Check if there is a point above and a point below, else
* it won't intersect.
*/
if (c->y <= a->y && c->y >= b->y) {
gCoord crossProduct;
/* If the line is parallel */
if (a->y == b->y) {
/* Point on the segment */
if ((c->x >= a->x && c->x <= b->x) || (c->x <= a->x && c->x >= b->x)) {
return 0;
} else {
return -1;
}
}
/* If the point is on the same horizontal line as one of the segment point,
* allow to add the intersection once
*/
if (c->y == b->y) {
return -1;
}
/* Matrix cross product to find if the point is left or right from the segment*/
crossProduct = (b->x - a->x) * (c->y - a->y) - (b->y - a->y) * (c->x - a->x);
/* Point left of the segment */
if (crossProduct < 0) {
return 1;
}
/* Point on the segment */
if (crossProduct == 0) {
return 0;
}
}
return -1;
}
gBool gmiscHittestPoly(const gPoint *pntarray, unsigned cnt, const gPoint *p) {
unsigned i = 0;
uint8_t nbrIntersection = 0;
int8_t crossResult;
// For each pair of points
for (i = 0; i < cnt-1; i++) {
/* Order the two points from top to bottom to simplify the function */
if (pntarray[i].y >= pntarray[i+1].y) {
crossResult = _pointCrossingSegment(&pntarray[i], &pntarray[i+1], p);
} else {
crossResult = _pointCrossingSegment(&pntarray[i+1], &pntarray[i], p);
}
/* Point on the edge of the polygon */
if (crossResult == 0) {
return gTrue;
}
/* Point crossing the polygon */
else if(crossResult == 1) {
nbrIntersection++;
}
}
/* Last pair of points, can't be done in the loops
* Same as before
*/
if (pntarray[cnt-1].y >= pntarray[0].y) {
crossResult = _pointCrossingSegment(&pntarray[cnt-1], &pntarray[0], p);
} else {
crossResult = _pointCrossingSegment(&pntarray[0], &pntarray[cnt-1], p);
}
if (crossResult == 0) {
return gTrue;
} else if(crossResult == 1) {
nbrIntersection++;
}
/* If we cross an even pair of segments, we are outside */
if (nbrIntersection % 2 == 0) {
return gFalse;
}
/* Else we are inside the polygon */
return gTrue;
}
#endif // GMISC_NEED_HITTEST_POLY
#endif // GFX_USE_GMISC
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