How to tell if one actor is "facing" another actor?

maxerov

I'm making a game where Actor 1 moves and turns randomly and when it faces Actor 2 an event is triggered. I have made a rudimentary system with complicated math but it has a lot of bugs and doesn't really work. Does anyone have any ideas as to how to do this?

jb15

You're using "VecterToAngle"? (Less than, and greater than)

For instance, if actor A's VecterToAngle to actor B (you'll need to constrain B's x and y as global attributes) is less than 180 and more than 0, then it's "facing" actor B.

Photics

Constrain an invisible actor to the main hero actor.

heroX
heroY
Rotation

Use COS/SIN to make that actor move in a circle.

If the other actors overlap with that actor, it's in the hero's line-of-sight.

If COS/SIN is scary to you, The Unofficial GameSalad Textbook has a great math chapter.

maxerov

I used this function: atan(( game.PlayerY - self.Position.Y )/( game.PlayerX - self.Position.X )) where PlayerX and PlayerY are global attributes (like you mentioned) that represent the Actor 2. self is Actor 1. I compared the results of this function to Actor 2's self.Rotation. Is VectorToAngle some sort of attribute in Gamesalad or is it a function I have to add myself?

maxerov

to Photics:
I was actually going to have it the other way around so that multiple instances of the Actor 2 would be looking for the Actor 1 (or hero actor). Would your system still work for that?

jb15

VecterToAngle gives you an angle between two points--as in, it tells you that actor A is at a 75 degree angle to actor B. If you look in the dropdown box in GS, it's there.

Photics

maxerov said:
to Photics:
I was actually going to have it the other way around so that multiple instances of the Actor 2 would be looking for the Actor 1 (or hero actor). Would your system still work for that?

I'm not sure about what you're exactly trying to do. There was a discussion about line of sight in another thread.

http://gamesalad.com/forums/topic.php?id=22982

I added line of sight to BOT. It works great. There's an invisible actor that does much of the work. It's position/rotation is constrained to TANK's X,Y and rotation data. The rest is just using rules to detect for overlaps.

maxerov

jb15 said:
VecterToAngle gives you an angle between two points--as in, it tells you that actor A is at a 75 degree angle to actor B. If you look in the dropdown box in GS, it's there.

Oh I see. Trying that it seems like it only gives me the angle between the actor and point (0,0). Is there a way to make show the angle between the two actors? Am I missing something?

Photics said:
I'm not sure about what you're exactly trying to do. There was a discussion about line of sight in another thread.

http://gamesalad.com/forums/topic.php?id=22982

I added line of sight to BOT. It works great. There's an invisible actor that does much of the work. It's position/rotation is constrained to TANK's X,Y and rotation data. The rest is just using rules to detect for overlaps.

Sorry for not being specific. I am trying to give enemies a "line of sight" so that something happens if they "see" the player. I thought about the method of just attaching an invisible sight actor to the enemies also. However, I don't know how I would get this method to work with multiple instances of the same enemy actor.

Photics

maxerov said:
Sorry for not being specific. I am trying to give enemies a "line of sight" so that something happens if they "see" the player. I thought about the method of just attaching an invisible sight actor to the enemies also. However, I don't know how I would get this method to work with multiple instances of the same enemy actor.

OH... you want to do the reverse. Now I understand.

That's tricky.

If self.rotation = vectorToAngle(TANK.X - Self.position.X , TANK.Y - Self.position.Y)
Then change self.aggressive to True

You could add a little bit of a variance too with two rules...

If self.rotation < vectorToAngle(TANK.X - Self.position.X , TANK.Y - Self.position.Y) +10

If self.rotation > vectorToAngle(TANK.X - Self.position.X , TANK.Y - Self.position.Y) -10

I'm not sure if this works, but it might be something to try.

jb15

You can change the numbers 0,0--even use global attributes.

maxerov

jb15 said:
You can change the numbers 0,0--even use global attributes.

Sorry stupid question. Thanks.

Photics said:
OH... you want to do the reverse. Now I understand.

That's tricky.

If self.rotation = vectorToAngle(TANK.X - Self.position.X , TANK.Y - Self.position.Y)
Then change self.aggressive to True

You could add a little bit of a variance too with two rules...

If self.rotation < vectorToAngle(TANK.X - Self.position.X , TANK.Y - Self.position.Y) +10

If self.rotation > vectorToAngle(TANK.X - Self.position.X , TANK.Y - Self.position.Y) -10

I'm not sure if this works, but it might be something to try.

That's about as far as I got (but vectorToAngle would have made it way easier haha). It gets complicated though because the way that vectorToAngle measures a rotation from say 3 o'clock to 6 o'clock counterclockwise it goes from 0° to -90° whereas if you rotate the object on its own (self.Rotation) it goes from 0° to 270°. So I guess it's time to brush up on my coordinate geometry.