Fast rectangle to rectangle intersection

Question

What's a fast way to test if 2 rectangles are intersecting?

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A search on the internet came up with this one-liner (WOOT!), but I don't understand how to write it in Javascript, it seems to be written in an ancient form of C++.

struct {     LONG    left;     LONG    top;     LONG    right;     LONG    bottom; } RECT;   bool IntersectRect(const RECT * r1, const RECT * r2) {     return ! ( r2->left > r1->right         || r2->right < r1->left         || r2->top > r1->bottom         || r2->bottom < r1->top         ); } 

Answer 1

This is how that code can be translated to JavaScript. Note that there is a typo in your code, and in that of the article, as the comments have suggested. Specifically r2->right left should be r2->right < r1->left and r2->bottom top should be r2->bottom < r1->top for the function to work.

function intersectRect(r1, r2) {   return !(r2.left > r1.right ||             r2.right < r1.left ||             r2.top > r1.bottom ||            r2.bottom < r1.top); } 

Test case:

var rectA = {   left:   10,   top:    10,   right:  30,   bottom: 30 };  var rectB = {   left:   20,   top:    20,   right:  50,   bottom: 50 };  var rectC = {   left:   70,   top:    70,   right:  90,   bottom: 90 };  intersectRect(rectA, rectB);  // returns true intersectRect(rectA, rectC);  // returns false