Entity flatness

Blitz3D Forums/Blitz3D Programming/Entity flatness

Picklesworth

(Posted 2004) [#1]

The paper discussion in OT reminded me of this little problem I have :)

I am trying to make a function that decides whether or not an entity will work as a convex hull, because the convex hull program doesn't like flat meshes and the bloody user never remembers this. So basically, it decides if a mesh is flat (regardless of its angle, etc.).

So, here is my function which doesn't work:

function isFlat(mesh,surface)

	if meshwidth(mesh) = 0 or meshheight(mesh) = 0 or meshdepth(mesh) = 0 then debuglog "IsFlat() Returns that entity is flat (via meshWidth() etc. check)" : return true

	LastX# = vertexX(surface,0)
	LastY# = vertexy(surface,0)

	LastZ# = vertexz(surface,0)
	
	Debuglog "Matching X: " + lastX#
	Debuglog "Matching Y: " + lastY#
	Debuglog "Matching Z: " + lastZ#
	
	ChangePitch# = 0
	ChangeYaw# = 0
	
	ChangedCount = 0

	for vert = 1 to countvertices(surface) - 1
	
		pass = false
	
		if vertexx(surface,vert) = LastX
			pass = true
			debuglog "X position the same. Vertex number " + vert
		else
			debuglog "X axis changed, leaving note"
			XChange = true
			
		endif
		
		if vertexy(surface,vert) = LastY
			pass = true
			debuglog "Y position the same. Vertex number " + vert
		else
			debuglog "Y axis changed, leaving note"
			YChange = true
		endif
		
		if vertexZ(surface,vert) = LastZ
			pass = true
			debuglog "Z position the same. Vertex number " + vert
		else
			debuglog "Z axis changed, leaving note"
			ZChange = true
		endif
		
		if XChange or YChange or ZChange
			if changedcount < 1 ;there can be one single position change without argument
				ChangedCount = ChangedCount + 1
				changepitch# = vectorpitch(lastX - vertexx(surface,vert),lastY - vertexy(surface,vert),lastZ - vertexZ(surface,vert))
				changeYaw# = vectoryaw(lastX - vertexx(surface,vert),lastY - vertexy(surface,vert),lastZ - vertexZ(surface,vert))
				pass = true
			else ;another position change will get argument, and will only work if it is still carrying along the same angle as the last one
				if ChangePitch# = vectorpitch(vertexx(surface,vert),vertexy(surface,vert),vertexZ(surface,vert)) and changeYaw# = vectoryaw(vertexx(surface,vert),vertexy(surface,vert),vertexZ(surface,vert))
					pass = true
				else
					pass = false
				endif
			endif
		endif
		
		if pass = false then debuglog "IsFlat() Returns that entity is not flat (via vertex section)" : return false
		
	next
	
	debuglog "IsFlat() Returns that entity is flat"		
	return true

end function

Sorry, there aren't many comments, but the debuglog entries help a bit.

I also haven't looked at this code recently and I sort of gave up halfway through so that's my early excuse for any stupid mistakes.

So, do you have a better way to do this or a way to fix this function?

Picklesworth

(Posted 2004) [#2]

If you don't know, say 'no' so that I know that this post was useless (but don't say 'no' if it's a dead post when you read this)

Beaker

(Posted 2004) [#3]

I would contruct a plane from every triangle, and then check every vert against each plane. If a vert is 'above' a plane (or on the plane maybe in your case) then the object is concave.

Is that what you want?

Picklesworth

(Posted 2004) [#4]

Sorry, I'm not entirely sure what you mean, Beaker...