CODEWITHSUNDEEP
c++mathcollision-detection
user987280
user987280

Reputation: 1608

rectangle collision

This is more of a programming problem than a technical question but since it relates to programming and math, I'm hoping to get some helpful feedback.

I have two rectangles: rectangle1 and rectangle2.

Both are defined by four float values:

float left;
float right;
float top;
float bottom;

For the sake of this example, say that each rectangle is 100 x 100 and that rectangle1 is:

float left = 100.0;
float right = 200.0;
float top = 500.0;
float bottom = 600.0;

And rectangle2 is:

float left = 150.0;
float right = 250.0;
float top = 550.0;
float bottom = 650.0;

When a collision occurs, I am trying to determine which side of rectangle1 hit which side of rectangle2 using the eight float values.

If my question was answered, I might be able to determine something like the following when a collision occurs:

rectangle1's right side hit rectangle2's left side

So far, I have tried using simple math to determine the distance between each possibility:

float distance1 = rectangle2.left - rectangle1.right;
float distance2 = rectangle2.top - rectangle1.bottom;
float distance3 = rectangle2.right - rectangle1.left;
float distance4 = rectangle2.bottom - rectangle1.top;

And then taking the minimum of those values to determine which side of each rectangle was involved in the collision. It doesn't seem so simple, though. There were two basic problems with this attempt:

1) The rectangles will already be overlapping by the time the collision code is reached.

2) If multiple rectangles are stacked on top of each other, the calculation will produce strange results (ie, even if rectangle1 is moving in the upper right direction and should hit both rectangles on their left side, it may actually hit one rectangle on the bottom and the other on the left.)

(This is because the rectangles are overlapping when the collision code is reached AND because distance1 and distance4 will be close or equal in this case.)

Is there a better way to answer this question using simple math? Any help would be appreciated.

And, before it's mentioned, this is not homework but a real problem I'm trying to solve for my game.

Upvotes: 0

Views: 733

Answers (1)

Ani
Ani

Reputation: 1655

If you can correctly identify the collision, then to determine the faces draw a line joining the center of the 2 rectangles and check for intersection with the faces of each rectangle. At any given time the line will intersect 2 faces as long as the 2 rectangles are not overlapping or to be precise, as long as the center of 1 is not inside the other.

When they are overlapping, you can get 1 or 0 intersection. case 0: 1 rectangle is totally inside the other so you can decide how you want to decide which sides are hitting, may be choose the one closest to each center.

case 1: rectangle is totally or partially inside the other. In either case, continue to extend your line joining the centers until you cross the outer (containing) rectangle. If u cross the contained rectangle before again, just change the hit face to the newly crossed face.

Hope its not too confusing :)

Upvotes: 1

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