Code archives/3D Graphics - Mesh/Removing Triangles and Vertices

This code has been declared by its author to be Public Domain code.

Download source code

Removing Triangles and Vertices by Mr Snidesmin
(Posted 23 years ago)
A few useful functions. Note: they will probably be slow for large meshes.

RemoveTriangle(surface%, triangle_index%)
-removes specified triangle from a surface

RemoveVertex(surface%, vertex_index%)
-removes specified vertex from a surface

VertexIsUsed(surface%, vi%)
-returns true if vertex index is used in a triangle.

ClearUnusedVertices%(surface%)
-removes unused vertices in a surface 
Function VertexIsUsed(surface%, vi%)
	For i% = 0 To CountTriangles(surface) - 1
		If TriangleVertex(surface, i, 0) = vi Then Return True
		If TriangleVertex(surface, i, 1) = vi Then Return True
		If TriangleVertex(surface, i, 2) = vi Then Return True
	Next
	Return False
End Function

Function ClearUnusedVertices%(surface%)
	For i% = 0 To CountVertices(surface) - 1
		If Not VertexIsUsed(surface, i) Then
			RemoveVertex surface, i
		End If
	Next
End Function


Function RemoveTriangle(surface%, triangle_index%)
	s0% = surface
	m% = CreateMesh()
	s% = CreateSurface(m)
	
	;copy, excluding triangle:
	For i% = 0 To CountVertices(s0)-1
		vi% = AddVertex(s, VertexX(s0, i),VertexY(s0, i),VertexZ(s0, i),VertexU(s0, i),VertexV(s0, i),VertexW(s0, i))
		VertexNormal s, vi, VertexNX(s0, i), VertexNY(s0, i), VertexNZ(s0, i)
		VertexColor s, vi, VertexRed(s0, i), VertexGreen(s0, i), VertexBlue(s0, i), VertexAlpha(s0, i)
	Next
	For i% = 0 To CountTriangles(s0)-1
		If i <> triangle_index Then
			AddTriangle s, TriangleVertex(s0, i, 0), TriangleVertex(s0, i, 1), TriangleVertex(s0, i, 2)
		End If
	Next
	
	;copy back
	CopySurface s, s0
	FreeEntity m
End Function


Function RemoveVertex(surface%, vertex_index%)
	s0% = surface
	m% = CreateMesh()
	s% = CreateSurface(m)
	
	;copy, excluding vertex:
	For i% = 0 To CountVertices(s0)-1
		If i <> vertex_index Then
			vi% = AddVertex(s, VertexX(s0, i),VertexY(s0, i),VertexZ(s0, i),VertexU(s0, i),VertexV(s0, i),VertexW(s0, i))
			VertexNormal s, vi, VertexNX(s0, i), VertexNY(s0, i), VertexNZ(s0, i)
			VertexColor s, vi, VertexRed(s0, i), VertexGreen(s0, i), VertexBlue(s0, i), VertexAlpha(s0, i)
		End If
	Next
	For i% = 0 To CountTriangles(s0)-1
		v0% = TriangleVertex(s0, i, 0)
		v1% = TriangleVertex(s0, i, 1)
		v2% = TriangleVertex(s0, i, 2)
		
		If v0 > vertex_index Then v0 = v0 - 1
		If v1 > vertex_index Then v1 = v1 - 1
		If v2 > vertex_index Then v2 = v2 - 1
		AddTriangle s, v0, v1, v2
	Next
	
	;copy back
	CopySurface s, s0
	FreeEntity m
End Function



Function CopySurface(source%, dest%, clear_unused_vertices%=False)
	s0% = source
	s% = dest
	ClearSurface s
	
	For i% = 0 To CountVertices(s0)-1
		vi% = AddVertex(s, VertexX(s0, i),VertexY(s0, i),VertexZ(s0, i),VertexU(s0, i),VertexV(s0, i),VertexW(s0, i))
		VertexNormal s, vi, VertexNX(s0, i), VertexNY(s0, i), VertexNZ(s0, i)
		VertexColor s, vi, VertexRed(s0, i), VertexGreen(s0, i), VertexBlue(s0, i), VertexAlpha(s0, i)
	Next
	For i% = 0 To CountTriangles(s0)-1
		AddTriangle s, TriangleVertex(s0, i, 0), TriangleVertex(s0, i, 1), TriangleVertex(s0, i, 2)
	Next
End Function