Gradually turn object to face a point in space

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Davey B

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Posted: 23rd Sep 2010 00:33

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I'm trying to create the ability for ai npcs to gradually turn to face the player before intercept.

I've cracked the code to do this on the x-z plane using:

+ Code Snippet

angle = ATANFULL( object position x(NPC(z).OBJECT) - object position x(active_ship), object position z(NPC(z).OBJECT) - object position z(active_ship))
            `Rotate object at a curveangle equating to ATANFULL
            yrotate object NPC(z).OBJECT,curveangle(angle, object angle y(NPC(z).OBJECT), 50)

This works well for X-Z but when I adapt this code for Y plane movement to something along the lines of:

+ Code Snippet

            angle2 = ATANFULL( object position x(NPC(z).OBJECT) - object position x(active_ship), object position y(NPC(z).OBJECT) - object position y(active_ship))
            `Rotate object at a curveangle equating to ATANFULL
            xrotate object NPC(z).OBJECT,curveangle(angle2, object angle x(NPC(z).OBJECT), 50)

Things mess up and the objects don't face the player in the y plane properly or at all. Does anybody know what i'm doing wrong? All I want is similar functionality to the point object command, but with some realism of the ai having to gradually turn...

Thanks in advance.

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Neuro Fuzzy

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Posted: 23rd Sep 2010 00:55 Edited at: 23rd Sep 2010 00:56

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Ah... you're a victim of 2d rotation easiness. 3d rotations are a bigger headache - especially what DBPro uses - euler rotations.

The problem you're looking to overcome is figuring out the angle one object needs to get to to point to another object. A problem you probably would run into later on is that euler angles interpolate badly (interpolating is just going smoothly from one value to another). Usually quaternion/axial rotation is used to overcome this.

I'm sure that's a lot of new terminology. If you want, you can google rotation matrices, euler angles, and a bunch of trig stuff - this'll get you the purely mathematical solution. Another choice would be to get EZ rotate - I've heard it's really good, and you'll have a whole host of commands to use - this won't be the last time you have trouble with 3d rotation.

Uhh, I'll try to think of another way to solve this (with built-in dbpro commands and not too math-intense stuff), but I don't really know :\

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Green Gandalf

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Playing: Malevolence:Sword of Ahkranox, Skyrim, Civ6.

Posted: 23rd Sep 2010 01:04 Edited at: 23rd Sep 2010 01:15

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I think you merely need to adjust two angles.

Try this:

+ Code Snippet

sync on : sync rate 60 : sync

autocam off
position camera 0, 50, -500
point camera 0, 25, 0

make object cube 1, 100 ` the npc
position object 1, 400, 400, 500

make object sphere 2, 50
position object 2, -100, 50, -200

repeat
  if inkey$() = "m" then position object 2, object position x(2)+0.4, object position y(2),object position z(2)
  angleX1# = object angle x(1)
  angleY1# = object angle y(1)
  angleZ1# = object angle z(1)
  point object 1, object position x(2), object position y(2), object position z(2)
  rotate object 1, curveangle(object angle x(1), angleX1#, 40.0), curveangle(object angle y(1), angleY1#, 40.0), angleZ1#
  sync
until spacekey()

end

Edit Actually this is better. Use the arrow keys to move the sphere:

+ Code Snippet

sync on : sync rate 60 : sync

autocam off
position camera 0, 50, -500
point camera 0, 25, 0

make object cube 1, 100 ` the npc
position object 1, 400, 400, 500

make object sphere 2, 50
position object 2, -100, 50, -200

repeat
  position object 2, object position x(2)+(rightkey()-leftkey())*2.0, object position y(2) + (upkey()-downkey())*2.0, object position z(2)
  angleX1# = object angle x(1)
  angleY1# = object angle y(1)
  angleZ1# = object angle z(1)
  point object 1, object position x(2), object position y(2), object position z(2)
  rotate object 1, curveangle(object angle x(1), angleX1#, 40.0), curveangle(object angle y(1), angleY1#, 40.0), angleZ1#
  sync
until spacekey()

end

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Davey B

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Posted: 24th Sep 2010 16:21

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Cheers guys.

@Gandalf - that solution works perfectly, thanks very much for that!

@Neuro - Yep this isnt the first time this stuff has caught me out. You solved another problem for me a few weeks back, its a real headache all this Euler angle stuff!...

Thnx for the help

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Neuro Fuzzy

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Posted: 25th Sep 2010 09:29

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Just an illustration of the problem I had stuck in my head:
http://forum.thegamecreators.com/?m=forum_view&t=176033&b=1

however what GG was doing is definitely better than worrying about tons o' rotation crap.

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Gael

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Posted: 27th Sep 2010 17:38

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If you want to calculate angles on the Common 0-360 range
try this :

distance_x=object_x-spectator_x
distance_y=spectator_y-object_y
angle_from_spectator=wrapvalue(atanfull(distance_y,distance_x))

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Green Gandalf

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Playing: Malevolence:Sword of Ahkranox, Skyrim, Civ6.

Posted: 27th Sep 2010 19:37

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You need two angles.

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