SyntaxBomb - Indie Coders

Hi.. im trying to distort a mesh by changing its vertix location..
but each time i do that i get the mesh polygons splitted..

for example a cube, will turn into 6 unattached polygones..
instead of a twisted cube as i desire..

i got threw all the vertex and all the surfaces  (in the cube case its only one surface..)

what am i doing wrong?

first i make a mesh vertex list..

	Method CreateMeshVertexsList:TList(Mesh)
		Local SurfNum, I, CurrentSurf, Vert, VertList:TList, VertHldr:VertHolder, Counter
		
		VertList = CreateList()
		
		SurfNum = xCountSurfaces(Mesh)
		
		For I = 1 To SurfNum
		
			CurrentSurf = xGetSurface(Mesh, I - 1)
			
			Counter = 0
			
			For Vert = 0 To xCountVertices(CurrentSurf) - 1
				
				VertHldr = New VertHolder
				
				VertHldr.SurfaceHandle = CurrentSurf

				VertHldr.X = xVertexX(CurrentSurf, Counter)
				VertHldr.y = xVertexY(CurrentSurf, Counter)
				VertHldr.z = xVertexZ(CurrentSurf, Counter)

				ListAddLast(VertList, VertHldr)
				
				Counter = Counter + 1
				
			Next
			
		Next
		
		Return VertList
	End Method

and than i randomize its location..

	Method WobbleMesh(MeshVertList:TList, Wob:Float = 0.15)
			Local Vert:VertHolder, Counter
	
			For Vert = EachIn MeshVertList
		
			 	xVertexCoords(Vert.SurfaceHandle, Counter, Vert.X + Cos(angle + Rnd(-20, 20)) * Wob, Vert.Y + Sin(angle + Rnd(-20, 20)) * Wob, Vert.Z)
	
				Counter = Counter + 1
				
			Next
			
			Angle = Angle + 1
			
			If Angle > 359 Then Angle = 0
			
		End Method

but i get a fragged cube instead of twisted..

cheers thanks

The cube will be unwelded so has 3 vertices at each corner.  If you want to distort the corners you must move all 3 to the same position OR use a welded cube where each face shares vertices with the others.

I think i get it.. Thanks..

Don't forget to normalize the vertice normals after any adjustment so that lighting works properly.

For a flat cube face, which is a plane, you do like this:

1. You want to pick any 3 of the 4 corners, think of them as corner A, corner B, corner C.
2. Create 2 vectors using them: A to B and from A to C, you do that by subtracting xyz of C from xyz of A, and also xyz of B from xyz of A.
3. When you have these two vectors you do a 'cross product' using them... this will give you a third vector that points outwards (or inwards, depending on how you form the previous 2 vectors).
4. Normalize this 3rd vector and the result is the face normal. As you want each of the 4 vertices to face the same way you use this value for those 4 vertex normals that make up that face. This is also why there are 3 different vertices at each corner - Each corner has 3 faces. Each vertex has only 1 normal for lighting so for those 3 faces you need 3 vertices at the same position but with a different normal facing different directions.
5. Rinse and repeat for 6 faces of the new shape.

For calculating the cross-product...
a. If you understand math notation then the wikipedia for Cross Product is the best source https://en.wikipedia.org/wiki/Cross_product
or b. If you want the calculation in a more layman language then math-is-fun is a good source https://www.mathsisfun.com/algebra/vectors-cross-product.html

You can use Pythagoras to calculate the length ( or magnitude ) of the vector and divide each component by the length for a normalized vector:
i. Local Length:Float = sqr(n.x * n.x + n.y * n.y + n.z * n.z) where n is the 3rd 'un-normalized' vector result from step 3 above.
ii. Divide each component by the length: n.x :/ length; n.y :/ length; n.z :/ length
iii. The result is a normalized vector for step 4 above.

ok thanks to you too col for all your effort..

You're welcome

Just wanted to mention (if others are interested too) that I'm sure you'll be quick to realise that most 3D models will be triangulated already which simplifies the code for doing the above.  A cube face will be made of 2 triangle polygons to form each flat square polygon. In which case each triangle polygon will only have 3 vertices anyway so no need to write code to pick 3 of the 4 vertices for each cube face. You still apply the exact same algorithm, just do it for every polygon and all will work out nice, clean and straight forward at the cost of calculating some vertex normals more than once.

Youve Done well man..
More or less i understood what you mean..
Ill deal with it when the time comes

Blimey, I think I'll stick to 2d 

Lol Steve..

Lol Steve..

i wasnt planing to get into it too deeply i i was just wondering why it splitted my cube..
i was certain a cube was made only from 8 vertex points but if each face is made of a different vertex that makes it more complex.. and heavy.

Is that Xors? If so, it should have a xUpdateNormals like Blitz3D does, which does something similar to what col mentioned. But in any case it's good to know how to do it manually, the cross product is very useful.

Not only normals but vertex colours and UVs can also cause the verts to be split (basically, any vertex attribute that can have a sharp change).
So I would run a loop once to gather all points that are located at the same places (collecting them in arrays, each for a set of points). This way you can move bunches of points at once, displacing them all together.

Totally, kryzon.. Simple and clear,, that's exactly what should be done..
Im not messing with this now but when i do thats what I'll do..

I was just wondering why my cube polygons get separated..
I didn't know each side has a separate polygon..
Doesn't that make the cube heavier?
Why did xors3d did that..

Because splitting vertices lets you get sharp edges, looks better.
The cube on the left is completely welded (8 vertices), cube on the right has split vertices (4 verts per face X 6 faces = 24 verts).

interesting.. didnt know that