关于C/C++游戏引擎如何判断碰撞(以SDL2为例)

SDL_LFPoint HitPoint2Line(SDL_LFPoint a1, SDL_LFPoint b1, SDL_LFPoint a2, SDL_LFPoint b2) {
    
    double fa1 = (a1.y - b1.y) / (a1.x - b1.x);
    double fa2 = a1.y - fa1 * a1.x;
    double fb1 = (a2.y - b2.y) / (a2.x - b2.x);
    double fb2 = a2.y - fb1 * a2.x;
    
    double x = (fb2 - fa2) / (fa1 - fb1);
    double y = fa1 * x + fa2;
    return { x, y };
}

bool Spirit::IsHitWith(const vector box) {
	if (box.empty() || this->hitBox.empty()) return false;
	for (int i = 0; i < this->hitBox.size(); i++) {
		qq_41726230::line la(
			this->rotateHitBox[i].x * this->size + this->place.x, this->rotateHitBox[i].y * this->size + this->place.y,
			this->rotateHitBox[i == this->rotateHitBox.size() - 1 ? 0 : i + 1].x * this->size + this->place.x,
			this->rotateHitBox[i == this->rotateHitBox.size() - 1 ? 0 : i + 1].y * this->size + this->place.y
		);
		for (int j = 0; j < box.size(); j++) {
			qq_41726230::line lb(
				box[j].x, box[j].y,
				box[j == box.size() - 1 ? 0 : j + 1].x,
				box[j == box.size() - 1 ? 0 : j + 1].y
			);
			if (qq_41726230::is_intersect(la, lb)) {
				return true;
			}
		}
	}

	//判断我是不是在他里面
	qq_41726230::line l1(this->rotateHitBox[0].x * this->size + this->place.x, this->rotateHitBox[0].y * this->size + this->place.y, -100, -100);
	int cnt[1] = {};
	for (int j = 0; j < box.size(); j++) {
		qq_41726230::line lb(
			box[j].x, box[j].y,
			box[j == box.size() - 1 ? 0 : j + 1].x,
			box[j == box.size() - 1 ? 0 : j + 1].y
		);
		int a = 0, b = 0;
		if (qq_41726230::is_intersect(l1, lb)) cnt[0]++;
		auto pos = HitPoint2Line({ l1.xa, l1.ya }, { l1.xb, l1.yb }, { lb.xa, lb.ya }, { lb.xb, lb.yb });
		if (pos.x == lb.xa && pos.y == lb.ya) {
			cnt[0]--;
		}
	}
	if (cnt[0] & 1) {
		return true;
	}
	//判断他是不是在我里面
	cnt[0] = 0;
	qq_41726230::line l6(box[0].x, box[0].y, -100, -100);
	for (int i = 0; i < this->hitBox.size(); i++) {
		qq_41726230::line la(
			this->rotateHitBox[i].x * this->size + this->place.x, this->rotateHitBox[i].y * this->size + this->place.y,
			this->rotateHitBox[i == this->rotateHitBox.size() - 1 ? 0 : i + 1].x * this->size + this->place.x,
			this->rotateHitBox[i == this->rotateHitBox.size() - 1 ? 0 : i + 1].y * this->size + this->place.y
		);
		if (qq_41726230::is_intersect(l6, la)) cnt[0]++;
		auto pos = HitPoint2Line({ l6.xa, l6.ya }, { l6.xb, l6.yb }, { la.xa, la.ya }, { la.xb, la.yb });
		if (pos.x == la.xa && pos.y == la.ya) {
			cnt[0]--;
		}
	}
	if (cnt[0] & 1) {
		return true;
	}
	//都不是
	return false;
}

void Spirit::SetDirection(double direction) {
    this->rotateHitBox.clear();
    for (int i = 0; i < this->hitBox.size(); i++) {
        this->rotateHitBox.push_back(CalcRotatePoint(this->hitBox[i], this->rotatePoint, direction));
    }
    this->dir = direction;
}
SDL_LFPoint CalcRotatePoint(const SDL_LFPoint& pos, const SDL_LFPoint& rpos, const double& direction) {
    SDL_LFPoint res;
    //thanks  kevin_org for https://blog.csdn.net/QIJINGBO123/article/details/100850088
    res.x = (pos.x - rpos.x) * cos(direction * 3.141593 / 180.0) - (pos.y - rpos.y) * sin(direction * 3.141593 / 180.0) + rpos.x;
    res.y = (pos.x - rpos.x) * sin(direction * 3.141593 / 180.0) + (pos.y - rpos.y) * cos(direction * 3.141593 / 180.0) + rpos.y;
    return res;
}

//Math.h
#pragma once
#include "Structure.h"
#include 
#include 
#include 
#include 

using namespace std;

//http://blog.sina.com.cn/s/blog_5d5c80840101bnhw.html
namespace ZH_CN_ZGY {
    
    extern pair PointToSegDistEx(double x, double y, double x1, double y1, double x2, double y2);
}

extern SDL_LFPoint PointToPolygonDistPos(SDL_LFPoint p, vector polygon);

extern SDL_LFPoint HitPoint2Line(SDL_LFPoint a1, SDL_LFPoint b1, SDL_LFPoint a2, SDL_LFPoint b2);

namespace mirro {
    extern double Tri(SDL_LFPoint p1, SDL_LFPoint p2);
}

extern SDL_LFPoint CirclePointCalc(double r, double angle, SDL_LFPoint mid);

//Math.cpp
#include "Math.h"

pair ZH_CN_ZGY::PointToSegDistEx(double x, double y, double x1, double y1, double x2, double y2) {
    double cross = (x2 - x1) * (x - x1) + (y2 - y1) * (y - y1);
    if (cross <= 0) return { sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1)), {x1, y1} };
    double d2 = (x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1);
    if (cross >= d2) return { sqrt((x - x2) * (x - x2) + (y - y2) * (y - y2)), {x2, y2} };
    double r = cross / d2;
    double px = x1 + (x2 - x1) * r;
    double py = y1 + (y2 - y1) * r;
    //bug fixed
    //return sqrt((x - px) * (x - px) + (py - y1) * (py - y1));
    return { sqrt((x - px) * (x - px) + (py - y) * (py - y)), {px, py} };
}

SDL_LFPoint PointToPolygonDistPos(SDL_LFPoint p, vector polygon) {
    double result_dis = 1e10;
    SDL_LFPoint result;
    for (int i = 0; i < polygon.size(); i++) {
        SDL_LFPoint a = polygon[i];
        SDL_LFPoint b = polygon[(i + 1) % polygon.size()];
        auto ret = ZH_CN_ZGY::PointToSegDistEx(p.x, p.y, a.x, a.y, b.x, b.y);
        if (ret.first < result_dis) {
            result_dis = ret.first;
            result = ret.second;
        }
    }
    return result;
}

SDL_LFPoint HitPoint2Line(SDL_LFPoint a1, SDL_LFPoint b1, SDL_LFPoint a2, SDL_LFPoint b2) {
    
    double fa1 = (a1.y - b1.y) / (a1.x - b1.x);
    double fa2 = a1.y - fa1 * a1.x;
    double fb1 = (a2.y - b2.y) / (a2.x - b2.x);
    double fb2 = a2.y - fb1 * a2.x;
    
    double x = (fb2 - fa2) / (fa1 - fb1);
    double y = fa1 * x + fa2;
    return { x, y };
}

//https://bbs.csdn.net/topics/391814854
namespace mirro {
    double Tri(SDL_LFPoint p1, SDL_LFPoint p2) {//形参是Point类的对象p1,p2
        double angle;
        if (p1.x == p2.x && p1.y < p2.y)
            return 90.0;//如果x坐标相等，p1的y值小于p2的y值，则方位角是90
        if (p1.x == p2.x && p1.y > p2.y)
            return 270.0;//如果x坐标相等，p1的y值大于p2的y值，则方位角是270
        if (p1.y == p2.y && p1.x < p2.x)
            return 0.0;//如果y坐标相等，p1的x值小于p2的x值，则方位角是180
        if (p1.y == p2.y && p1.x > p2.x)
            return 180.0;//如果y坐标相等，p1的x值大于p2的x值，则方位角是180
        angle = atan((p1.y - p2.y) / (p1.x - p2.x)) * (180.0 / M_PI); //得到弧度制的角
        if (p1.x < p2.x && p1.y < p2.y)
            return angle; //标准情况下正常输出。
        if (p1.x > p2.x)
            return 180.0 + angle;//angle正负都有可能。
        if (p1.x < p2.x && p1.y > p2.y)
            return 360.0 + angle;//angle是负值。
        return -999;
    }
}

SDL_LFPoint CirclePointCalc(double r, double angle, SDL_LFPoint mid) {
    return {
        mid.x + r * cos((angle - 90) * M_PI / 180.0),
        mid.y + r * sin((angle - 90) * M_PI / 180.0)
    };
}

//Structure.h
#pragma once

struct SDL_LFPoint {
	double x, y;
};
struct SDL_LFRect {
	double x, y, w, h;
};

//Spirit.h
#pragma once
#include "Structure.h"
#include "Math.h"
#include 
#include 
#include