Faster Collisions Circles or Squares? Advice. (Fixed)

EnlightenedOne · 2009-09-10T14:55:18

Hi there I have been looking around trying to create an efficient means of having things in my 2D top down asteroids rebuild colliding. Now the trouble is do I use circles or squares to do the collisions?! I have done some research... as you will soon see. This is quite a long post so I can understand anyone wishing to skim read. Im working with C++ in DX9. Firstly I dont care where particularly the shapes touch with circle collisions the direction you collide with an object at is going to be the direction your moving in as that is a an angle. With squares im sure it would take more effort I am curious to see if anyone has an effective way of iscolating that as the squares collision is tested. Circles involve finding the distance between the two shapes and then identifying their combined radius value to see if the two points in 2d space are touching. Circles Example. ------------------------------------- A = x,y, radius B = x,y, radius FIND THE DISTANCE To find the distance between the two you need too. Find the smaller of the x and y values. Take the smaller x and y values away from the larger x and y values. Square them. Add them together. Find the square root of the value you have combined, tada you have the distance. IDENTIFY COLLISION Add the radius values of the two objects your testing between. Take the radius values away from the distance and if you have a negative value your objects are touching! Squares involve identifying when one border of one side of either of the two objects has overlapped another border of the other square. Squares Example. ------------------------------------- A = x, y, width, height; B = x, y, width, height; This is abit drawn out to describe but basically I think you need. Assuming the square never rotates. My game involves squares so I was wondering if anyone could provide a more flexible or intelligent solution for such collisions which is more efficient! Here an idealic solution. if A.Right < B.Left or A.Left > B.Right or A.Top < B.Bottom or A.Bottom > B.Top Translating in nerdy form to. if objectA.x + objectA.width < objectB.x or objectA.x > objectB.x + objectB.width or objectA.y < objectB.y + objectB.height or objectA.y + objectA.height > objectB.y However this idealic solution is flawed. You can be parallel to an object in one direction and yet be on another axes very far away. So you need to create a logical square at the edge of your shapes borders to identify if one edge has been touched by another, this requires there to be 4 logical statements based on the squares side it varies abit but you just need to pick a side and its easy enough to interpret. That is one if statement with 4 logical statements in there as and statements. To iscolate every side. If you look up at the simple Right < Left idealic concept then you multiply every time you see a direction by 4 thats 32 logical statements for every single collision detection for none rotating squares that is not pretty. Has anyone got a better way to show me? Analysis?, corrections? HELP! ------------------------------------------- At the moment I am thinking one or the other but perhaps combining both is although more complicated more ideal for the game. Additionally Orientating a squares collision box based on the direction of my space ship would be nicer than having it be based purely around square the texture is drawn into. How can I make a circle register being hit by a square? I am going to have to go into overlapping verticies for such collisions is that efficient for a 2D game? I am aware im going to have to play with that stuff anyway in the real world when I go 3D but I was hoping to meet that wall after I am comfortable with particle systems. Advice? [Edited by - EnlightenedOne on September 10, 2009 4:15:57 PM]

For Beginners

Started by EnlightenedOne September 07, 2009 08:15 AM

12 comments, last by Atrix256 14 years, 7 months ago

Aezon

106

September 09, 2009 05:10 PM

Now that the question is resolved, I would like to make a comment:

When you were describing the distance formula, I actually was momentarily lost. You won't have to worry about losing most of the people on here if you simply state the formula, because most people on here know what it is.(square root((x2-x1)^2+(y2-y1)^2) is a good way to do it.)

Thank you.

-----------------------Are you breaking into the world of game development, and are finding yourself lost?I am also a beginner, whose here to get lost-and find his way back-for you. Check out my blog You will(hopefully) learn bunches, alongside me.*Last update: 1/1/10*New Theme!

EnlightenedOne

143

Author

September 10, 2009 02:29 PM

Well I started looking over your code Captain P thinking it would not work for some reason I seem to have a terrible time getting to grips with a relatively simple concept and im not entirely sure why myself. I had the preconception that the code would only meet all the conditions if one square was ontop of the other I had to do example to get it through my head. But yes thank you for pointing out how terribly unnecessary that would have been.

I will include a formula representation of anything I am going over in the future calculations Aezon :)

EnlightenedOne

143

Author

September 10, 2009 02:52 PM

Out of curiosity what does AABB stand for?

Atrix256

540

September 10, 2009 02:55 PM

it stands for "Axis aligned bounding box". An AABB is made up of a minimum point and a maximum point and the walls of the box are all paralel with an axis but it doesn't have to be square.

you might also see another term "OBB" which stands for "Oriented bounding box" which is just a rotated AABB.

HTH! (:

Faster Collisions Circles or Squares? Advice. (Fixed)

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Faster Collisions Circles or Squares? Advice. (Fixed)

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines