CODEWITHSUNDEEP
c++algorithm2dcollision-detectionphysics
sgtHale
sgtHale

Reputation: 1557

2D Static Box Collision with variable terrain

Im working on a 2D game in which the terrain can vary and is composed of any shape of polygons except for self intersecting ones. The player collision box is in the shape of a square and can move about. My question is this: How do I keep an always-upright box to collide with variable terrain and always stay outside?

My current approach that I made up albeit no code yet works like the following:

prototype

The blue square is the player hitbox. First, it moves with a velocity downwards as an example. My goal is to find the heighest point in its travel path where it can be safely outside of the terrain polygon. I test all the terrain vertex points inside its travel path and project them to the velocity of the box. I take the farthest projection.

The farthest projection will be the max distance allowed to move in without going into the terrain.

Move the square by distance in the direction of velocity and done.

However, there are few scenarios that I encountered where this does not work. Take this as an example:

Failure of algorithm

To remedy this situation, I now test for one corner of the square. If the distance from the corner is shorter than the farthest projection, then that distance will give the appropriate shift in distance. This pretty much makes the algorithm full-proof. Unless someone states another exception.

Im going a little crazy and I would appreciate feedback on my algorithm. If anyone has any suggestions or good reads about 2D upright box collisions on terrain or anything similar, that would be great.

Upvotes: 1

Views: 614

Answers (1)

Art Gower
Art Gower

Reputation: 213

This may be useful, and here I'll quickly elaborate on "upright" square collision.

First the collision may occur on the side of the square, and not necessarily a corner. A simple solution to check any collision is describe the region delimited by the square, and then check if any point of your uneven terrain is within this region.

To define the square region, assume your upright square is has the corners (x1,y1), (x2,y1), (x2,y2), (x1,y2), where x2>x1 and y2>y1. Then for a point (x,y) to be within the square it needs to satisfy the conditions 

If( x1< x < x2 and y1< y <y2) Then (x,y) is in the square.

Then to conclude, all you need do is check if any point on the terrain satisfies the above condition. Good luck.

Upvotes: 1

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