CODEWITHSUNDEEP
c++geometry
Andrei Gradinaru
Andrei Gradinaru

Reputation: 35

Can't determine if two squares/rectangles are intersecting each other

As a online graphical I used: https://www.khanacademy.org/computer-programming/spin-off-of-rectx-y-width-height-radius/4975791745220608

The rectangle coordinates:

rectangle 1: x: 180 y: 30

rectangle 2: x: 160 y: 30

What I noticed is that the render begins from a point and is increased on X axis by width and Y axis by height. So i deduced the following things: x1 and y1 are equal to rectangle coordinates (x1 and y1 being the top left corner) and x2, y2 are the bottom right corner/coordinates which are equal to the sum of square coordinates or in other words x1 and y1 and the width & height of the square.

That's the code i made:

#include <stdio.h>
#include <iostream>

struct A
{
    int x1, x2;
    int y1, y2;
};

struct B 
{
    int x1, x2;
    int y1, y2;
};

bool doOverlap(A a, B b)
{
    if (a.x1 < b.x2 && a.x2 > b.x1 &&
        a.y1 > b.y2 && a.y2 < b.y1)
        return true;

    return false;
}

int main()
{
    /* 
        Rectangle 1 coords: X: 180 Y: 30
        Rectangle 2 coords: X: 160 Y: 30
    */
    
    A a;
    B b;

    /* 
        The render begins from top left corner (that's our center and
        from here begins the render with +width on x and +heigth on y
        (correct me in case i'm wrong but that's what i noticed: https://imgur.com/a/nZKBB0m
        (as can you see in that photo, the white rectangle has l1: (x,y): 0 0)

        rectangles are 40x40
    */
    a.x1 = 180;
    a.y1 = 30;
    a.x2 = a.x1 + 40;
    a.y2 = a.y1 + 40;

    b.x1 = 160;
    b.y1 = 30;
    b.x2 = b.x1 + 40;
    b.y2 = b.y1 + 40;

    if (doOverlap(a, b))
    {
        std::cout << "y";
    }
    else
        std::cout << "n";
   
    return 0;
}

The problem is it always return false (checked a lot of codes but no one of them seems like are working) So,what do i do wrong?

Upvotes: 0

Views: 103

Answers (1)

Cosmin Petolea
Cosmin Petolea

Reputation: 119

You're only checking if a is above above b, and then checking if a is left of b. You need to check if the x intervals of a and b overlap, and then check if the y intervals overlap. Here is a way of doing that:

bool doOverlap(A a, B b)
{
    if (a.x1 > b.x2 || b.x1 > a.x2)
        return false;
    if (a.y1 > b.y2 || b.y1 > a.y2)
        return false;
    return true;
}

The first if checks if the x intervals of a and b overlap, and returns false if they don't. The second does the same for the y intervals. If both the x and y intervals overlap, the rectangles overlap

Upvotes: 2

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