Util.cpp

#include "Util.h"

//Box collision detector
bool checkCollision(SDL_Rect a, SDL_Rect b)
{
	//The sides of the rectangles
	int leftA, leftB;
	int rightA, rightB;
	int topA, topB;
	int bottomA, bottomB;

	//Claculate the sides of rect A
	leftA = a.x;
	rightA = a.x + a.w;
	topA = a.y;
	bottomA = a.y + a.h;

	//Calculate the sides of rect B
	leftB = b.x;
	rightB = b.x + b.w;
	topB = b.y;
	bottomB = b.y + b.h;

	//If any of the dsides from A are outside of B
	if (bottomA <= topB) { return false; }
	if (topA >= bottomB) { return false; }
	if (rightA <= leftB) { return false; }
	if (leftA >= rightB) { return false; }

	//If none of the sides from A are outside of B
	return true;
}//end static check collision method

//Per Pixel collision detector
bool checkCollision(std::vector<SDL_Rect>& a, std::vector<SDL_Rect>& b)
{
	//The sides of the rectangles
	int leftA, leftB;
	int rightA, rightB;
	int topA, topB;
	int bottomA, bottomB;

	//Go though the boxes
	for (int Abox = 0; Abox < a.size(); Abox++)
	{
		//Calculate the sides of rect A
		leftA = a[Abox].x;
		rightA = a[Abox].x + a[Abox].w;
		topA = a[Abox].y;
		bottomA = a[Abox].y + a[Abox].h;
		//Go though the B boxes
		for (int Bbox = 0; Bbox < b.size(); Bbox++)
		{
			//Calculate the sides of rect A
			leftB = b[Bbox].x;
			rightB = b[Bbox].x + b[Bbox].w;
			topB = b[Bbox].y;
			bottomB = b[Bbox].y + b[Bbox].h;

			//If no sides from A are outside of B
			if (((bottomA <= topB) || (topA >= bottomB) ||
				(leftA >= rightB) || (rightA <= leftB)) == false)
			{
				//A collision is detected
				return true;
			}//end if collision is deteched
		}//end Bbox Loop
	}//end Abox Loop

	//If neither set of collision boxes touched
	return false;
}//end per pixel collision detection method

//Circle/Circle collision detector
bool checkCollision(Circle& a, Circle& b)
{
	//Calculate total radius squared
	int totalRadiusSquared = a.r + b.r;
	totalRadiusSquared *= totalRadiusSquared;

	//If the distance between the centers of the circles is less than the sum of their radii
	if (distanceSquared(a.x, a.y, b.x, b.y) < (totalRadiusSquared))
	{
		//The circles have collided
		return true;
	}

	//if not 
	return false;
}//end check circle circle collision method

//Circle/Box collision detector
bool checkCollision(Circle& a, SDL_Rect& b)
{
	//Closest point on vollision box
	int cX, cY;

	//Find closest x offset
	if (a.x < b.x)
	{
		cX = b.x;
	}
	else if (a.x > b.x + b.w)
	{
		cX = b.x + b.w;
	}
	else
	{
		cX = a.x;
	}

	//Find closest y offset
	if (a.y < b.y)
	{
		cY = b.y;
	}
	else if (a.y > b.y + b.h)
	{
		cY = b.y + b.h;
	}
	else
	{
		cY = a.y;
	}

	//If the closest point is inside the circle
	if (distanceSquared(a.x, a.y, cX, cY) < a.r * a.r)
	{
		//This box and cirlce have collided
		return true;
	}

	//If not
	return false;
}//end check circle to square collision method

//Calculates distance squared between two points
double distanceSquared(int x1, int y1, int x2, int y2)
{
	int deltaX = x2 - x1;
	int deltaY = y2 - y1;

	return deltaX*deltaX + deltaY*deltaY;
}