Can't understand IK...

[Wolfears2]

Ok, to cut things short:
I know what inverse kinematics are
I just about (sort of) understand the math.
I just want to keep some points a set distance apart, don't care about rotation. I can do all the instances and movieclip names myself, I'm not a complete noob =P
Any help?

[Wolfears2]

wow, are they that complicated?

[Coaly]

I'm not sure what you're asking, but the basic idea is to find the angle from point A to point B, and then adjust point B's position using the angle and whatever distance you choose.

[dELtaluca]

At 5/14/08 04:02 PM, Coaly wrote: I'm not sure what you're asking, but the basic idea is to find the angle from point A to point B, and then adjust point B's position using the angle and whatever distance you choose.

although if all you are wanting is a distance constraint, then that is totally unnecesary, and its much faster executing to use a bit of vector math, take the vector between the two points, and rescale it to match the required distance.

[greenkube]

I was playing around with IK stuff about a month ago and found a good example in some AS2 code, so I converted it to a couple of classes and updated it to AS3.

Here is what I use as my Document Class:

package {
	import flash.display.MovieClip;

	public class IKChain extends MovieClip {
		
		protected var numOfNodes:Number = 10;
		
		public function IKChain() {
			CreateNodes();
		}
		
		protected function CreateNodes():void
		{
			for (var c = 0; c < numOfNodes; c++)
			{
				var myNode:Node = new Node(stage.stageWidth, stage.stageHeight, c);
				this.addChild(myNode);
			}
			
			var firstNode = this.getChildByName("node0");
			firstNode.nodes.push(this.getChildByName("node1"));
			
			for ( var b = 1; b < numOfNodes - 1; b++)
			{ 
				myNode = Node(this.getChildByName("node" + b));
				myNode.nodes.push(this.getChildByName("node" + (b - 1)));
				myNode.nodes.push(this.getChildByName("node" + (b + 1)));
			}
		
			var lastNode = this.getChildByName("node" + (numOfNodes - 1));
			lastNode.nodes.push(this.getChildByName("node" + (numOfNodes - 2)));
			
			firstNode.Move(firstNode, null);
		}
	}
}

And here is what I refer to as my Node class for each node. You need to link the items you want chained together in your linkage to the Node class:

package {
	import flash.display.MovieClip;

	public class IKChain extends MovieClip {
		
		protected var numOfNodes:Number = 10;
		
		public function IKChain() {
			CreateNodes();
		}
		
		protected function CreateNodes():void
		{
			for (var c = 0; c < numOfNodes; c++)
			{
				var myNode:Node = new Node(stage.stageWidth, stage.stageHeight, c);
				this.addChild(myNode);
			}
			
			var firstNode = this.getChildByName("node0");
			firstNode.nodes.push(this.getChildByName("node1"));
			
			for ( var b = 1; b < numOfNodes - 1; b++)
			{ 
				myNode = Node(this.getChildByName("node" + b));
				myNode.nodes.push(this.getChildByName("node" + (b - 1)));
				myNode.nodes.push(this.getChildByName("node" + (b + 1)));
			}
		
			var lastNode = this.getChildByName("node" + (numOfNodes - 1));
			lastNode.nodes.push(this.getChildByName("node" + (numOfNodes - 2)));
			
			firstNode.Move(firstNode, null);
		}
	}
}

Hope this helps you get a jump start on the idea.

[greenkube]

Sorry, I just realized I posted the IKChain class twice, here is the node class:

package {
	import flash.display.MovieClip;
	import flash.events.Event;
	import flash.events.MouseEvent;
	
	public class Node extends MovieClip {
		
		public var nodes:Array = new Array();
		public var distance:Number = 50;
		
		public function Node(stageWidth:Number, stageHeight:Number, nodeNumber:Number) {
			this.x = Math.random() * stageWidth;
			this.y = Math.random() * stageHeight;
			this.name = "node" + nodeNumber;
			LoadEvents();
		}	
		
		protected function LoadEvents():void
		{
			this.addEventListener(MouseEvent.MOUSE_DOWN, NodeMouseDown);
			this.addEventListener(MouseEvent.MOUSE_UP, NodeMouseUp);
		}
		
		protected function NodeMouseDown(e:MouseEvent):void
		{
			this.addEventListener(Event.ENTER_FRAME, MouseMove);	
		}
		
		protected function NodeMouseUp(e:MouseEvent):void
		{
			this.removeEventListener(Event.ENTER_FRAME, MouseMove);
		}
		
		public function MouseMove(e:Event):void
		{	
			this.x = stage.mouseX;
			this.y = stage.mouseY;
			Move(this, null);
		}
		
		public function Move(myNode:Node, parentNode:Node):void
		{
			for (var c = 0; c < myNode.nodes.length; c++)
			{
				if (parentNode == null || Node(myNode.nodes[c]).name != parentNode.name)
				{
					MakeChildMove(Node(myNode.nodes[c]), myNode);
					Move(Node(myNode.nodes[c]), myNode);
				}
			}
		}
		
		public function MakeChildMove(childNode:Node, parentNode:Node)
		{
			var dx = childNode.x - parentNode.x;
			var dy = childNode.y - parentNode.y;
			var alpha = Math.atan2(dy, dx);
			childNode.x = parentNode.x + Math.cos(alpha) * distance;
			childNode.y = parentNode.y + Math.sin(alpha) * distance;
			childNode.rotation = (Math.PI + alpha) * 180 / Math.PI;
		}
	}
}

[Wolfears2]

At 5/14/08 04:54 PM, greenkube wrote: Sorry, I just realized I posted the IKChain class twice, here is the node class:

package {
import flash.display.MovieClip;...

Is all that AS3? I'm using a older version of flash, so I can't use that if it is.

[GustTheASGuy]

It is obviously and you don't need to. Use it as reference. Though really I'd say you're probably too stupid to use IK if you can't port a hundred lines of code.

[greenkube]

At 5/15/08 08:07 AM, GustTheASGuy wrote: It is obviously and you don't need to. Use it as reference. Though really I'd say you're probably too stupid to use IK if you can't port a hundred lines of code.

Damn thats harsh. IK can be a tricky thing to grasp, especially if you are looking at for the first time.

[GustTheASGuy]

To a beginner probably. My issue is when people briefly state that the suggested that is clearly sufficient is not a working solution therefore they need something better.

[greenkube]

At 5/15/08 11:23 AM, GustTheASGuy wrote: To a beginner probably. My issue is when people briefly state that the suggested that is clearly sufficient is not a working solution therefore they need something better.

True, I can agree with that.