Collision Detection on table of objects (without physics)

Solar2D General Questions/Discussion
#1

I am making a game in which there are multiple enemies (up to at least 3 at a time). I create the enemies using a table and I can detect collision with the main character already. Here is the issue:

Each enemy type has a different ID associated with it with different effects. When there are multiple enemies on the screen at a time and one collides with the main character, then the IDs for the enemies get switched and the wrong effect occurs. Any ideas as to why?

In the code, first I create the enemy then add it into the table. Then I check for collisions in a different function using a for loop.

#2

I’m sorry I’m not able to help you, but I’d really like to know how you got the collision detection to work. I’ve been looking a this all day and following tutorials that it can find.

#3

I’ve never been a fan of collision detection using physics when it’s the only reason you use physics.  It’s a lot of overhead, body creation, etc. just to get collision events.   I personally use more programmatic ways of doing this.   Please see this blog post I wrote a couple of years ago:

http://omnigeek.robmiracle.com/2011/12/14/collision-detection-without-physics/

It gives you a couple of different ways to determine if two rectangles are touching each other or to see if two circles are in the same space but it does require using a Runtime enterFrame listener or if you’re doing touch and drag you can do the detection in the moved phase of the touch handler.

These two methods are a couple of the easiest to implement.  There are also point in rectangle checks and more complex  polygon detection (though I didn’t get that working for Lua).

#4

That just happens to be the tutorial that I actually used to solve my problem!

I ended up modifying it to fit my needs because I didn’t want to change majority of my code if I didn’t have to. The main part that solved my problem though was to add a flag to check when the collision is being tested, so that only one enemy collision could be checked at a time.

To test for collisions, I used two transparent rectangles (one for the front and one for the back) since I have enemies coming from both sides of the main character. This is the main piece of the code that I modified:

[lua]local left = (back.x - enemy.x) <= 10 and (back.x - enemy.x) >= -10
local right = (front.x - enemy.x) <= 10 and (front.x - enemy.x) >= -10

return (left or right)[/lua]

In the method I send in my enemies table item (enemies[a]) and it checks for each one at a time.

Performance isn’t the best though, as the enemies end up pausing in place on the screen, and I can’t figure out why this is or how to fix it. But it works great, thanks to that link in the answer above.

#5

I’m sorry I’m not able to help you, but I’d really like to know how you got the collision detection to work. I’ve been looking a this all day and following tutorials that it can find.

#6

I’ve never been a fan of collision detection using physics when it’s the only reason you use physics.  It’s a lot of overhead, body creation, etc. just to get collision events.   I personally use more programmatic ways of doing this.   Please see this blog post I wrote a couple of years ago:

http://omnigeek.robmiracle.com/2011/12/14/collision-detection-without-physics/

It gives you a couple of different ways to determine if two rectangles are touching each other or to see if two circles are in the same space but it does require using a Runtime enterFrame listener or if you’re doing touch and drag you can do the detection in the moved phase of the touch handler.

These two methods are a couple of the easiest to implement.  There are also point in rectangle checks and more complex  polygon detection (though I didn’t get that working for Lua).

#7

That just happens to be the tutorial that I actually used to solve my problem!

I ended up modifying it to fit my needs because I didn’t want to change majority of my code if I didn’t have to. The main part that solved my problem though was to add a flag to check when the collision is being tested, so that only one enemy collision could be checked at a time.

To test for collisions, I used two transparent rectangles (one for the front and one for the back) since I have enemies coming from both sides of the main character. This is the main piece of the code that I modified:

[lua]local left = (back.x - enemy.x) <= 10 and (back.x - enemy.x) >= -10
local right = (front.x - enemy.x) <= 10 and (front.x - enemy.x) >= -10

return (left or right)[/lua]

In the method I send in my enemies table item (enemies[a]) and it checks for each one at a time.

Performance isn’t the best though, as the enemies end up pausing in place on the screen, and I can’t figure out why this is or how to fix it. But it works great, thanks to that link in the answer above.