newton polygon to triangles

BlitzMax Forums/BlitzMax Programming/newton polygon to triangles

UNZ	(Posted 2013) [#1]

Hi,

I'm totally confused here. I try to render the newton game dynamics collision meshes. But unfortunately newton does not save this data in as triangles.

I have a callback ( based on code from http://irrlicht.sourceforge.net/forum/viewtopic.php?t=37024 ) that is run for every polygon of the mesh:

'-----------------------------------------------------
Function NewtonCollisionIterator(bodyPtr:Byte Ptr, vertexCount:Int, faceArray:Float[], faceId:Int)
polyCount:+1
	
	DebugLog "vertex count:"+vertexCount
	For Local i:Int = 0 To vertexCount-1
		DebugLog "v:"+faceArray[i]
	Next
	
	'render as wireframe
	Local color:SColor = _SCOLOR(0, 255, 0, 0)
	Local line:Vector3df
	
	local i:Int= vertexCount - 1
	Local p0:Vector3df = _VECTOR3DF(faceArray[(i * 3 + 0)], ..
									faceArray[(i * 3 + 1)], ..
									faceArray[(i * 3 + 2)])
	Local p1:Vector3df
	
	For i = 0 To vertexCount - 1
		
		p1 = _VECTOR3DF(faceArray[((i + 1) * 3 + 0)], ..
						faceArray[((i + 1) * 3 + 1)], ..
						faceArray[((i + 2) * 3 + 2)])
		driver.draw3DLine(p0, p1, color)
		
		p0= p1
	Next
End Function

which gives me this data:

DebugLog:vertex count:4
DebugLog:v:1.00000000
DebugLog:v:1.00000000
DebugLog:v:-1.00000000
DebugLog:v:-1.00000000
DebugLog:vertex count:4
DebugLog:v:-1.00000000
DebugLog:v:1.00000000
DebugLog:v:1.00000000
DebugLog:v:-1.00000000
DebugLog:vertex count:4
DebugLog:v:1.00000000
DebugLog:v:-1.00000000
DebugLog:v:1.00000000
DebugLog:v:1.00000000
DebugLog:vertex count:4
DebugLog:v:-1.00000000
DebugLog:v:1.00000000
DebugLog:v:-1.00000000
DebugLog:v:-1.00000000
DebugLog:vertex count:4
DebugLog:v:-1.00000000
DebugLog:v:-1.00000000
DebugLog:v:1.00000000
DebugLog:v:-1.00000000
DebugLog:vertex count:4
DebugLog:v:1.00000000
DebugLog:v:-1.00000000
DebugLog:v:-1.00000000
DebugLog:v:-1.00000000

obviously I try to render a cube here. What I need now are tris.

The function should transform the arrays to vertices to render a line between each pair of p0,p1.

Problem is that this doesn't work in Bmax. faceArray[i * 3 + 0] is out of the array size sometimes and the value is 0.0 then (but it doesn't crash). I don't know why this should work in c++.

Anyway the information of the tris is there (6 faces with 4 corners sounds promising). But how can I transform it to the form i need?

Floyd

(Posted 2013) [#2]

EDIT: If you saw what I wrote before you can ignore it. I misunderstood the objective. I will try again soon.

Okay, I think it's just a matter of the p1 index being "off by 1".

	For i = 0 To vertexCount - 1
		
		p1 = _VECTOR3DF(faceArray[i * 3 + 0], ..
						faceArray[i * 3 + 1], ..
						faceArray[i * 3 + 2])
		driver.draw3DLine(p0, p1, color)
		
		p0= p1
	Next

That should get rid of the "out of bounds" problem. But this looks like it is just drawing the polygon defined by the vertices, in this case a square.

To triangulate each face you probably need something like this, in pseudocode.

p0 = vertex at position vertexCount-1, as before.
For i = 0 To vertexCount - 2
	p1 = vertex at position i in the list
	p2 = vertex at position i+1
	Add triangle p0,p1,p2 to the triangle list
Next

I have no experience with Newton and don't know how to actually deal with triangles.

UNZ	(Posted 2013) [#3]

I got it!

The code that works:

'-----------------------------------------------------
Function NewtonCollisionIterator(bodyPtr:Byte Ptr, vertexCount:Int, faceArray:Float ptr, faceId:Int)

	DebugLog "vertex count:"+vertexCount
	For Local i:Int = 0 To vertexCount-1
		DebugLog "v:"+faceArray[i * 3 ]+","+faceArray[i * 3 + 1]+","+faceArray[i * 3 + 2]
	Next


	Local i:Int= vertexCount-1
	Local color:SColor = _SCOLOR(255,255,0,0)
	Local p0:Vector3df = _VECTOR3DF(faceArray[i * 3 + 0], ..
									faceArray[i * 3 + 1], ..
									faceArray[i * 3 + 2])
	Local p1:Vector3df
	
	For i = 0 To vertexCount - 1
		p1 = _VECTOR3DF(faceArray[i * 3 + 0], ..
						faceArray[i * 3 + 1], ..
						faceArray[i * 3 + 2])
		driver.draw3DLine(p0, p1, color)
		p0 = p1
	Next
End Function

What is the difference here? It is in the parameters. I declared faceArray as float ptr instead of float array (I thought that would be equivalent ?!). Anyway, now the values make much more sense and aren't 0.0 anymore.

And the shapes are quads of course not tris. My bad.

bye