collision.cpp

/*
 * File:   collision.cpp
 * Author: Nick
 *
 * Created on 30 January 2009, 11:02
 */
#include <SFML/Graphics.hpp>
#include "collision.hpp"

Collision::Collision() {
}

Collision::~Collision() {
}

sf::IntRect Collision::GetAABB(const sf::Sprite& Object) {

    //Get the top left corner of the sprite regardless of the sprite's center
    //This is in Global Coordinates so we can put the rectangle back into the right place
    sf::Vector2f pos = Object.TransformToGlobal(sf::Vector2f(0, 0));

    //Store the size so we can calculate the other corners
    sf::Vector2f size = Object.GetSize();

    float Angle = Object.GetRotation();

    //Bail out early if the sprite isn't rotated
    if (Angle == 0.0f) {
        return sf::IntRect(static_cast<int> (pos.x),
                static_cast<int> (pos.y),
                static_cast<int> (pos.x + size.x),
                static_cast<int> (pos.y + size.y));
    }

    //Calculate the other points as vectors from (0,0)
    //Imagine sf::Vector2f A(0,0); but its not necessary
    //as rotation is around this point.
    sf::Vector2f B(size.x, 0);
    sf::Vector2f C(size.x, size.y);
    sf::Vector2f D(0, size.y);

    //Rotate the points to match the sprite rotation
    B = RotatePoint(B, Angle);
    C = RotatePoint(C, Angle);
    D = RotatePoint(D, Angle);

    //Round off to int and set the four corners of our Rect
    int Left = static_cast<int> (MinValue(0.0f, B.x, C.x, D.x));
    int Top = static_cast<int> (MinValue(0.0f, B.y, C.y, D.y));
    int Right = static_cast<int> (MaxValue(0.0f, B.x, C.x, D.x));
    int Bottom = static_cast<int> (MaxValue(0.0f, B.y, C.y, D.y));

    //Create a Rect from out points and move it back to the correct position on the screen
    sf::IntRect AABB = sf::IntRect(Left, Top, Right, Bottom);
    AABB.Offset(static_cast<int> (pos.x), static_cast<int> (pos.y));
    return AABB;
}

float Collision::MinValue(float a, float b, float c, float d) {
    float min = a;

    min = (b < min ? b : min);
    min = (c < min ? c : min);
    min = (d < min ? d : min);

    return min;
}

float Collision::MaxValue(float a, float b, float c, float d) {
    float max = a;

    max = (b > max ? b : max);
    max = (c > max ? c : max);
    max = (d > max ? d : max);

    return max;
}

sf::Vector2f Collision::RotatePoint(const sf::Vector2f& Point, float Angle) {
    Angle = Angle * RADIANS_PER_DEGREE;
    sf::Vector2f RotatedPoint;
    RotatedPoint.x = Point.x * cos(Angle) + Point.y * sin(Angle);
    RotatedPoint.y = -Point.x * sin(Angle) + Point.y * cos(Angle);
    return RotatedPoint;
}

bool Collision::PixelPerfectTest(const sf::Sprite& Object1, const sf::Sprite& Object2, sf::Uint8 AlphaLimit) {
        //Get AABBs of the two sprites
    sf::IntRect Object1AABB = GetAABB(Object1);
    sf::IntRect Object2AABB = GetAABB(Object2);

    sf::IntRect Intersection;

    if (Object1AABB.Intersects(Object2AABB, &Intersection)) {

        //We've got an intersection we need to process the pixels
        //In that Rect.

        //Bail out now if AlphaLimit = 0
        if (AlphaLimit == 0) return true;

        //There are a few hacks here, sometimes the TransformToLocal returns negative points
        //Or Points outside the image.  We need to check for these as they print to the error console
        //which is slow, and then return black which registers as a hit.

        sf::IntRect O1SubRect = Object1.GetSubRect();
        sf::IntRect O2SubRect = Object2.GetSubRect();

        sf::Vector2i O1SubRectSize(O1SubRect.GetWidth(), O1SubRect.GetHeight());
        sf::Vector2i O2SubRectSize(O2SubRect.GetWidth(), O2SubRect.GetHeight());

        sf::Vector2f o1v;
        sf::Vector2f o2v;
        //Loop through our pixels
        for (int i = Intersection.Left; i < Intersection.Right; i++) {
            for (int j = Intersection.Top; j < Intersection.Bottom; j++) {

                o1v = Object1.TransformToLocal(sf::Vector2f(i, j)); //Creating Objects each loop :(
                o2v = Object2.TransformToLocal(sf::Vector2f(i, j));

                //Hack to make sure pixels fall withint the Sprite's Image
                if (o1v.x > 0 && o1v.y > 0 && o2v.x > 0 && o2v.y > 0 &&
                        o1v.x < O1SubRectSize.x && o1v.y < O1SubRectSize.y &&
                        o2v.x < O2SubRectSize.x && o2v.y < O2SubRectSize.y) {

                    //If both sprites have opaque pixels at the same point we've got a hit
                    if ((Object1.GetPixel(static_cast<int> (o1v.x), static_cast<int> (o1v.y)).a > AlphaLimit) &&
                            (Object2.GetPixel(static_cast<int> (o2v.x), static_cast<int> (o2v.y)).a > AlphaLimit)) {
                        return true;
                    }
                }
            }
        }
        return false;
    }
    return false;
}

bool Collision::CircleTest(const sf::Sprite& Object1, const sf::Sprite& Object2) {
    //Simplest circle test possible
    //Distance between points <= sum of radius

    float Radius1 = (Object1.GetSize().x + Object1.GetSize().y) / 4;
    float Radius2 = (Object2.GetSize().x + Object2.GetSize().y) / 4;
    float xd = Object1.GetPosition().x - Object2.GetPosition().x;
    float yd = Object1.GetPosition().y - Object2.GetPosition().y;

    return sqrt(xd * xd + yd * yd) <= Radius1 + Radius2;
}

//From Rotated Rectangles Collision Detection, Oren Becker, 2001

bool Collision::BoundingBoxTest(const sf::Sprite& Object1, const sf::Sprite& Object2) {

    sf::Vector2f A, B, C, BL, TR;
    sf::Vector2f HalfSize1 = Object1.GetSize();
    sf::Vector2f HalfSize2 = Object2.GetSize();

    //For somereason the Vector2d divide by operator
    //was misbehaving
    //Doing it manually
    HalfSize1.x /= 2;
    HalfSize1.y /= 2;
    HalfSize2.x /= 2;
    HalfSize2.y /= 2;
    //Get the Angle we're working on
    float Angle = Object1.GetRotation() - Object2.GetRotation();
    float CosA = cos(Angle * RADIANS_PER_DEGREE);
    float SinA = sin(Angle * RADIANS_PER_DEGREE);

    float t, x, a, dx, ext1, ext2;

    //Normalise the Center of Object2 so its axis aligned an represented in
    //relation to Object 1
    C = Object2.GetPosition();

    C -= Object1.GetPosition();

    C = RotatePoint(C, Object2.GetRotation());

    //Get the Corners
    BL = TR = C;
    BL -= HalfSize2;
    TR += HalfSize2;

    //Calculate the vertices of the rotate Rect
    A.x = -HalfSize1.y*SinA;
    B.x = A.x;
    t = HalfSize1.x*CosA;
    A.x += t;
    B.x -= t;

    A.y = HalfSize1.y*CosA;
    B.y = A.y;
    t = HalfSize1.x*SinA;
    A.y += t;
    B.y -= t;

    t = SinA * CosA;

    // verify that A is vertical min/max, B is horizontal min/max
    if (t < 0) {
        t = A.x;
        A.x = B.x;
        B.x = t;
        t = A.y;
        A.y = B.y;
        B.y = t;
    }

    // verify that B is horizontal minimum (leftest-vertex)
    if (SinA < 0) {
        B.x = -B.x;
        B.y = -B.y;
    }

    // if rr2(ma) isn't in the horizontal range of
    // colliding with rr1(r), collision is impossible
    if (B.x > TR.x || B.x > -BL.x) return false;

    // if rr1(r) is axis-aligned, vertical min/max are easy to get
    if (t == 0) {
        ext1 = A.y;
        ext2 = -ext1;
    }// else, find vertical min/max in the range [BL.x, TR.x]
    else {
        x = BL.x - A.x;
        a = TR.x - A.x;
        ext1 = A.y;
        // if the first vertical min/max isn't in (BL.x, TR.x), then
        // find the vertical min/max on BL.x or on TR.x
        if (a * x > 0) {
            dx = A.x;
            if (x < 0) {
                dx -= B.x;
                ext1 -= B.y;
                x = a;
            } else {
                dx += B.x;
                ext1 += B.y;
            }
            ext1 *= x;
            ext1 /= dx;
            ext1 += A.y;
        }

        x = BL.x + A.x;
        a = TR.x + A.x;
        ext2 = -A.y;
        // if the second vertical min/max isn't in (BL.x, TR.x), then
        // find the local vertical min/max on BL.x or on TR.x
        if (a * x > 0) {
            dx = -A.x;
            if (x < 0) {
                dx -= B.x;
                ext2 -= B.y;
                x = a;
            } else {
                dx += B.x;
                ext2 += B.y;
            }
            ext2 *= x;
            ext2 /= dx;
            ext2 -= A.y;
        }
    }

    // check whether rr2(ma) is in the vertical range of colliding with rr1(r)
    // (for the horizontal range of rr2)
    return !((ext1 < BL.y && ext2 < BL.y) ||
            (ext1 > TR.y && ext2 > TR.y));

}