Starting with model hierarchy and matrices

Other Standards COLLADA
1

Hi, I am implementing Collada support into my engine. I have an XML parser running, and I am able to go through the Collada nodes. I want to start by loading the model hierarchy, and matrix information, to make sure I have the model limb orientations all correct.

Please explain how. I have looked at the tutorials and if there is any useful information in there, it is extremely well-hidden. I am programming in BlitzMax, by the way.

Here is what I have so far:

Import bah.libxml

LoadDAE("duck.dae")

Global COLLADA_UpAxis

Function LoadDAE(file$)

	Local doc:TxmlDoc
	doc = TxmlDoc.parseFile(file)
	
	If Not doc
		Notify "Failed to load file.",1
		End
	EndIf
	
	Local root:TxmlNode = doc.getRootElement() 
	Notify root.GetName()
	
	For Cur_node:TxmlNode = EachIn root.Getchildren()
		Select Cur_Node.GetName()
			Case "asset" ParseAsset(doc,Cur_node)
			Case "library_materials"
			Case "library_geometries"
			Case "library_visual_scenes"
			Case "scene"
			Case "library_images"
			Case "library_cameras"	'don't care
			Case "library_lights"	'don't care
			Case "library_effects"	'don't care
			Default					'unknown
		EndSelect
	Next
	
	Function ParseAsset(doc:TxmlDoc,Cur_node:TxmlNode)
		Local ch:TxmlNode
		Local ch_list:TList
		ch_list= Cur_node.GetChildren() 
		If ch_list
			For ch=EachIn ch_list 
				Select ch.GetName().toLower() 
					Case "up_axis"
						Select ch.GetContent() 
							Case "X_UP"
								COLLADA_UpAxis=0
							Case "Y_UP"
								COLLADA_UpAxis=1
							Case "Z_UP"
								COLLADA_UpAxis=2
						EndSelect
				End Select
			Next
		EndIf
		Notify COLLADA_UpAxis
	EndFunction
	
EndFunction
2

I have looked at the tutorials
I’m not sure what tutorials you’re referring to, but you should be looking at the Collada spec.

In Collada, each node has a set of transforms, and you can imagine combining them into a local transform matrix.

<node id="N1">
    <translate>...</translate>
    <rotate>...</rotate>
    <scale>...</scale>
</node>

Convert the transform elements to matrices T, R, and S, and the local transform matrix will be N1 = TRS

Nodes can be nested arbitrarily deep of course.

<node id="N1">
    ...
    <node id="N2">
        ...
        <node id="N3">
            ...
            <instance_geometry url="#G">...</instance_geometry>

Here, the transform to apply to geometry G will be N1N2N3.

Here I’m assuming we’re using column vectors, as in OpenGL. For row vectors (Direct3D) you would reverse the multiplication order.

Then you have the <up_axis> setting. You want to import the model so that it matches your world’s up axis. You can do that simply by rotating the whole model into your world’s coordinate frame.

Steve

3

After having looked further into the way mesh data and referencing is done in this format, I have decided to make the DirectX .x file format my main file format. Sorry for the trouble.