problem met when checking collision between circle and polygon using SAT - c

Question

I try to use SAT to check collision between circle and polygon, it works well when the circle is near the edges (of polygon), however when circle is closet to the corners (of polygon), it is push inside, and outside after that.
under this it failed
but under such cases it works well
How to solve this?
the algorithm looks like this:
double mtv = DBL_MAX; // minimum translation vector
Vector2 minAxis;
foreach(Edge e in p.Edges)
{
var axis = e.normal;
var circleInterval = ProjectInterval(c, axis);
var polygonInterval = ProjectInterval(p, axis);
float overlap = OverlapIntervals(circleInterval, polygonInterval);
if(overlap < 0)
{
//the intervals overlap if it returns a positive number
return -1.0f;
}
if(overlap < mtv)
{
mtv = overlap;
minAxis = e.normal;
}
}
and my code is here:
static AS_UNUSED inline AS_Bool AS_SAT_test_polygon_circle(AS_Polygon *poly, AS_Circle *circle, AS_Result *result) {
AS_Vector *axis_normed = AS_vector_create(0, 0);
if (result) {
result->is_overlapping = AS_TRUE;
result->shape_a = poly;
result->shape_b = circle;
result->type_a = AS_POLYGON;
result->type_b = AS_CIRCLE;
}
for (int i = 0; i < array_len(poly->coords); i++) {
AS_Vector *coord1 =poly->coords[i];
AS_Vector *coord2 = poly->coords[i + 1 >= array_len(poly->coords) ? 0 : i + 1];
axis_normed->x = coord1->x - coord2->x;
axis_normed->y = coord1->y - coord2->y;
AS_vector_perp(axis_normed);
AS_vector_norm(axis_normed);
double min1 = DBL_MAX, max1 = -DBL_MAX;
double dot_product;
for (int j = 0; j < array_len(poly->coords); j++) {
dot_product = AS_vector_dot(poly->coords[j], axis_normed);
if (dot_product > max1) max1 = dot_product;
if (dot_product < min1) min1 = dot_product;
}
double b = AS_vector_dot(circle->position, axis_normed);
double a = b - circle->radius, c = b + circle->radius;
double min2, max2;
min2 = a < b ? a : b;
min2 = min2 < c ? min2 : c;
max2 = a > b ? a : b;
max2 = max2 > c ? max2 : c;
if (result) {
double overlap;
if (min1 < min2) {
result->a_in_b = AS_FALSE;
if (max1 < min2) {
result->is_overlapping = AS_FALSE;
return AS_FALSE;
} else if (max1 < max2) {
overlap = max1 - min2;
} else {
double option1 = max1 - min2;
double option2 = max2 - min1;
overlap = option1 < option2 ? option1 : option2;
}
} else {
result->b_in_a = AS_FALSE;
if (max2 < min1) {
result->is_overlapping = AS_FALSE;
return AS_FALSE;
} else if (max2 < max1) {
overlap = max2 - min1;
} else {
double option1 = max2 - min1;
double option2 = max1 - min2;
overlap = option1 < option2 ? option1 : option2;
}
}
if (overlap < result->overlap) {
result->overlap = overlap;
result->overlap_x = axis_normed->x;
result->overlap_y = axis_normed->y;
}
} else {
if (min1 > max2 || min2 > max1) {
return AS_FALSE;
}
}
}
return AS_TRUE;
}

Answer 1

Simply add add a check about closest point of the polygon, that will be okay.