Physics.cpp

#include "Physics.h"
#include "Components.h"

Vec2 Physics::GetOverlap(std::shared_ptr<Entity> a, std::shared_ptr<Entity> b)
{
    auto x1 = a->getComponent<CTransform>()->pos.x;
    auto y1 = a->getComponent<CTransform>()->pos.y;
    auto x2 = b->getComponent<CTransform>()->pos.x;
    auto y2 = b->getComponent<CTransform>()->pos.y;
    Vec2 delta(abs(x1-x2), abs(y1-y2));
    auto w1 = a->getComponent<CBoundingBox>()->halfSize.x;
    auto h1 = a->getComponent<CBoundingBox>()->halfSize.y;
    auto w2 = b->getComponent<CBoundingBox>()->halfSize.x;
    auto h2 = b->getComponent<CBoundingBox>()->halfSize.y;
    auto ox = w1 + w2 - delta.x;
    auto oy = h1 + h2 - delta.y;
    return Vec2(ox, oy);
}

Vec2 Physics::GetPreviousOverlap(std::shared_ptr<Entity> a, std::shared_ptr<Entity> b)
{
    auto x1 = a->getComponent<CTransform>()->prevPos.x;
    auto y1 = a->getComponent<CTransform>()->prevPos.y;
    auto x2 = b->getComponent<CTransform>()->prevPos.x;
    auto y2 = b->getComponent<CTransform>()->prevPos.y;
    Vec2 delta(abs(x1-x2), abs(y1-y2));
    auto w1 = a->getComponent<CBoundingBox>()->halfSize.x;
    auto h1 = a->getComponent<CBoundingBox>()->halfSize.y;
    auto w2 = b->getComponent<CBoundingBox>()->halfSize.x;
    auto h2 = b->getComponent<CBoundingBox>()->halfSize.y;
    auto ox = w1 + w2 - delta.x;
    auto oy = h1 + h2 - delta.y;
    return Vec2(ox, oy);
}

Intersect Physics::LineIntersect(const Vec2 & a, const Vec2 & b, const Vec2 & c, const Vec2 & d)
{
    Vec2 r = (b - a);
    Vec2 s = (d - c);
    float rxs = r * s;
    Vec2 cma = c - a;
    float t = (cma * s) / rxs;
    float u = (cma * r) / rxs;

    if (t >= 0.0 && t <= 1.0 && u >= 0.0 && u <= 1.0)
        return { true, Vec2(a.x + t*r.x, a.y + t*r.y) };
    else
        return { false, Vec2(0.0, 0.0) };
}

bool Physics::EntityIntersect(const Vec2 & a, const Vec2 & b, std::shared_ptr<Entity> e)
{
    Vec2 halfSize = e->getComponent<CBoundingBox>()->halfSize;
    Vec2 pos = e->getComponent<CTransform>()->pos;

    Vec2 c = Vec2(pos.x - halfSize.x, pos.y - halfSize.y);
    Vec2 d = Vec2(pos.x + halfSize.x, c.y);
    Intersect i1 = LineIntersect(a, b, c, d);

    d = Vec2(c.x, pos.y + halfSize.y);
    Intersect i2 = LineIntersect(a, b, c, d);

    c = Vec2(pos.x + halfSize.x, pos.y - halfSize.y);
    d = Vec2(c.x, pos.y + halfSize.y);
    Intersect i3 = LineIntersect(a, b, c, d);

    c = Vec2(pos.x - halfSize.x, pos.y + halfSize.y);
    d = Vec2(pos.x + halfSize.x, c.y);
    Intersect i4 = LineIntersect(a, b, c, d);

    return i1.result || i2.result || i3.result || i4.result;
}