StarCap/Collision.cpp

/*
 * File:   collision.cpp
 * Author: Nick (original version), ahnonay (SFML2 compatibility), bmorgan1 (collsion point return)
 */

#include <map>
#include "Collision.h"

namespace Collision
{
    class BitmaskManager
    {
    public:
        ~BitmaskManager() {
            std::map<const sf::Texture*, sf::Uint8*>::const_iterator end = Bitmasks.end();
            for (std::map<const sf::Texture*, sf::Uint8*>::const_iterator iter = Bitmasks.begin(); iter!=end; iter++)
                delete [] iter->second;
        }

        sf::Uint8 GetPixel (const sf::Uint8* mask, const sf::Texture* tex, unsigned int x, unsigned int y) {
            if (x>tex->getSize().x||y>tex->getSize().y)
                return 0;

            return mask[x+y*tex->getSize().x];
        }

        sf::Uint8* GetMask (const sf::Texture* tex) {
            sf::Uint8* mask;
            std::map<const sf::Texture*, sf::Uint8*>::iterator pair = Bitmasks.find(tex);
            if (pair==Bitmasks.end())
            {
                sf::Image img = tex->copyToImage();
                mask = CreateMask (tex, img);
            }
            else
                mask = pair->second;

            return mask;
        }

        sf::Uint8* CreateMask (const sf::Texture* tex, const sf::Image& img) {
            sf::Uint8* mask = new sf::Uint8[tex->getSize().y*tex->getSize().x];

            for (unsigned int y = 0; y<tex->getSize().y; y++)
            {
                for (unsigned int x = 0; x<tex->getSize().x; x++)
                    mask[x+y*tex->getSize().x] = img.getPixel(x,y).a;
            }

            Bitmasks.insert(std::pair<const sf::Texture*, sf::Uint8*>(tex,mask));

            return mask;
        }
    private:
        std::map<const sf::Texture*, sf::Uint8*> Bitmasks;
    };

    BitmaskManager Bitmasks;

    bool PixelPerfectTest(const sf::Sprite& Object1, const sf::Sprite& Object2, sf::Uint8 AlphaLimit, sf::Vector2f &point) {
        sf::FloatRect Intersection;
        if (Object1.getGlobalBounds().intersects(Object2.getGlobalBounds(), Intersection)) {
            sf::IntRect O1SubRect = Object1.getTextureRect();
            sf::IntRect O2SubRect = Object2.getTextureRect();

            sf::Uint8* mask1 = Bitmasks.GetMask(Object1.getTexture());
            sf::Uint8* mask2 = Bitmasks.GetMask(Object2.getTexture());

            // Loop through our pixels
            for (int i = Intersection.left; i < Intersection.left+Intersection.width; i++) {
                for (int j = Intersection.top; j < Intersection.top+Intersection.height; j++) {

                    sf::Vector2f o1v = Object1.getInverseTransform().transformPoint(i, j);
                    sf::Vector2f o2v = Object2.getInverseTransform().transformPoint(i, j);

                    // Make sure pixels fall within the sprite's subrect
                    if (o1v.x > 0 && o1v.y > 0 && o2v.x > 0 && o2v.y > 0 &&
                        o1v.x < O1SubRect.width && o1v.y < O1SubRect.height &&
                        o2v.x < O2SubRect.width && o2v.y < O2SubRect.height) {

                        if (Bitmasks.GetPixel(mask1, Object1.getTexture(), (int)(o1v.x)+O1SubRect.left, (int)(o1v.y)+O1SubRect.top) > AlphaLimit &&
                            Bitmasks.GetPixel(mask2, Object2.getTexture(), (int)(o2v.x)+O2SubRect.left, (int)(o2v.y)+O2SubRect.top) > AlphaLimit) {
                            point = sf::Vector2f(i, j);
                            return true;
                        }
                    }
                }
            }
        }
        return false;
    }

    bool CreateTextureAndBitmask(sf::Texture &LoadInto, const std::string& Filename)
    {
        sf::Image img;
        if (!img.loadFromFile(Filename))
            return false;
        if (!LoadInto.loadFromImage(img))
            return false;

        Bitmasks.CreateMask(&LoadInto, img);
        return true;
    }

    sf::Vector2f GetSpriteCenter (const sf::Sprite& Object)
    {
        sf::FloatRect AABB = Object.getGlobalBounds();
        return sf::Vector2f (AABB.left+AABB.width/2.f, AABB.top+AABB.height/2.f);
    }

    sf::Vector2f GetSpriteSize (const sf::Sprite& Object)
    {
        sf::IntRect OriginalSize = Object.getTextureRect();
        sf::Vector2f Scale = Object.getScale();
        return sf::Vector2f (OriginalSize.width*Scale.x, OriginalSize.height*Scale.y);
    }

    bool CircleTest(const sf::Sprite& Object1, const sf::Sprite& Object2) {
        sf::Vector2f Obj1Size = GetSpriteSize(Object1);
        sf::Vector2f Obj2Size = GetSpriteSize(Object2);
        float Radius1 = (Obj1Size.x + Obj1Size.y) / 4;
        float Radius2 = (Obj2Size.x + Obj2Size.y) / 4;

        sf::Vector2f Distance = GetSpriteCenter(Object1)-GetSpriteCenter(Object2);

        return (Distance.x * Distance.x + Distance.y * Distance.y <= (Radius1 + Radius2) * (Radius1 + Radius2));
    }

    class OrientedBoundingBox // Used in the BoundingBoxTest
    {
    public:
        OrientedBoundingBox (const sf::Sprite& Object) // Calculate the four points of the OBB from a transformed (scaled, rotated...) sprite
        {
            sf::Transform trans = Object.getTransform();
            sf::IntRect local = Object.getTextureRect();
            Points[0] = trans.transformPoint(0.f, 0.f);
            Points[1] = trans.transformPoint(local.width, 0.f);
            Points[2] = trans.transformPoint(local.width, local.height);
            Points[3] = trans.transformPoint(0.f, local.height);
        }

        sf::Vector2f Points[4];

        void ProjectOntoAxis (const sf::Vector2f& Axis, float& Min, float& Max) // Project all four points of the OBB onto the given axis and return the dotproducts of the two outermost points
        {
            Min = (Points[0].x*Axis.x+Points[0].y*Axis.y);
            Max = Min;
            for (int j = 1; j<4; j++)
            {
                float Projection = (Points[j].x*Axis.x+Points[j].y*Axis.y);

                if (Projection<Min)
                    Min=Projection;
                if (Projection>Max)
                    Max=Projection;
            }
        }
    };

    bool BoundingBoxTest(const sf::Sprite& Object1, const sf::Sprite& Object2) {
        OrientedBoundingBox OBB1 (Object1);
        OrientedBoundingBox OBB2 (Object2);

        // Create the four distinct axes that are perpendicular to the edges of the two rectangles
        sf::Vector2f Axes[4] = {
                sf::Vector2f (OBB1.Points[1].x-OBB1.Points[0].x,
                              OBB1.Points[1].y-OBB1.Points[0].y),
                sf::Vector2f (OBB1.Points[1].x-OBB1.Points[2].x,
                              OBB1.Points[1].y-OBB1.Points[2].y),
                sf::Vector2f (OBB2.Points[0].x-OBB2.Points[3].x,
                              OBB2.Points[0].y-OBB2.Points[3].y),
                sf::Vector2f (OBB2.Points[0].x-OBB2.Points[1].x,
                              OBB2.Points[0].y-OBB2.Points[1].y)
        };

        for (int i = 0; i<4; i++) // For each axis...
        {
            float MinOBB1, MaxOBB1, MinOBB2, MaxOBB2;

            // ... project the points of both OBBs onto the axis ...
            OBB1.ProjectOntoAxis(Axes[i], MinOBB1, MaxOBB1);
            OBB2.ProjectOntoAxis(Axes[i], MinOBB2, MaxOBB2);

            // ... and check whether the outermost projected points of both OBBs overlap.
            // If this is not the case, the Separating Axis Theorem states that there can be no collision between the rectangles
            if (!((MinOBB2<=MaxOBB1)&&(MaxOBB2>=MinOBB1)))
                return false;
        }
        return true;
    }
}