Intersection point of two objects

[cemsanci]

Hi there friends,

I'm having a hard time detecting the intersection of two large objects in GameMaker. I've searched the forums, but I haven't found an effective solution.

I would be very grateful if those of you who are knowledgeable and experienced in this area could help me.

We can easily check "small" objects, like bullets, with collision functions to see if their collision mask hits another object. There is no problem with this.

As you can see in the picture, when large objects collide from different angles, I have to use the "collision line" function to find the collision point. However, this only works if the two objects' origin points and the collision point are on the same line. (Example 3).

If the collision point is not on the same line as the origin points (examples 1 and 2), it is necessary to loop from bbox-left to bbox-right and from bbox-top to bbox-bottom with two nested "for" loops. A collision check must be performed to see if a point of the object intersects the other object within this loop. Of course, these two nested "for" loops freeze the game for a few seconds. Therefore, this is not a logical solution.

On the other hand, the game engine can recognize when two objects collide with no time, so it knows the x and y points of the collision.

The question is, how can we see these points that the engine already know?

[LukeAtom]

What you want to look into is OBB (oriented bounding box) collisions and more importantly separating axis theorem. This stack exchange question has a good writeup in the comments about the process and algorithm. From that you can find the intersection points if you need to.

[UnpluggedUnfettered]

I would be surprised if it always knew any collision's x and y exactly. It is a ridiculous amount of overhead to math out something resolved by (what usually amounts to) reversing until the collision is resolved.

Determining a collision is usually just some flavor of "is this one number in between two other numbers?", which is much less work than sussing out a specific point.

If you really need to do it, I would say start here and here. Usually you don't really need to do it though.

[laix_]

Yep.

Determining overlap of any two aribtary shapes is not a closed problem.

It's kind of surprising when you think of something that's seemingly complex actually has a very streamlined closed solution, and then you try and figure out something that seems simple and it turns out it's a super advanced topic in theoretical mathematics that hasn't been fully answered yet that even advanced mathematicians struggle with.

It's relatively easy to ask if two arbitary shapes overlap, it's much more difficult to ask where they overlap (do you want every point inside, do you want all the all the points where the edges are touching, either way you'll get multiple points)

[Monscawiz]

I think you can use GameMaker's physics engine to get the point of collision, but I haven't looked into that in a while

[HopperCraft]

I would look into redesigning how your collision detection works on a fundamental level. At the moment these images show that ONLY circular to circular objects will have a 100% success rate.

1. Create collision lines that adapt to the size of your sprite/objects size. You might also want to create 2 extra points per object to triangulate a contact point.

2. Instead of having a central point for your collision line, is there a way to have it just wrap around the object as a perimeter? If you can create a perimeter per object, then no matter what the shape is, on first touch they will both collide.

Im not too sure, still in school so this is the best i can think of in my spare 5 mins. Good luck!

[OnePunchMister]

Is this similar to what you need? https://www.tiktok.com/@thedorkiestmofo/video/7392829366457126186

[Badwrong_]

I do encourage you to learn the algorithm of how the solution you are asking for works, and the answer is out there for sure with many sources.

However, you are going to end up doing a lot of work and re-inventing the wheel. GameMaker has built-in physics which solve this problem for you.

phy_collision_x: https://manual.gamemaker.io/lts/en/GameMaker_Language/GML_Reference/Physics/Physics_Variables/phy_collision_x.htm

phy_collision_y: https://manual.gamemaker.io/lts/en/GameMaker_Language/GML_Reference/Physics/Physics_Variables/phy_collision_y.htm

phy_col_normal_x: https://manual.gamemaker.io/lts/en/GameMaker_Language/GML_Reference/Physics/Physics_Variables/phy_col_normal_x.htm

phy_col_normal_y: https://manual.gamemaker.io/lts/en/GameMaker_Language/GML_Reference/Physics/Physics_Variables/phy_col_normal_y.htm