Code archives/3D Graphics - Misc/Alpha Zorder

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

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Alpha Zorder by Beaker
(Posted 23 years ago)
Unlike normal and masked ones, Blitz doesn't sort alpha'd triangles, which leads
to far away objects appearing in front of near ones. 'Alpha Zorder' rectifies this
by sorting triangles, but only when needed. This makes it incredibly fast.

It's great for large numbers of trees and grass that contain some alpha mesh/textures.

Setup is slow at first, but it is possible to save the sorted data (code not included), so it is only calculated once.

There is a demo of the system here:
http://www.blitzbasic.com/codearcs/codearcs.php?code=807

One day I hope that programs like the excellent Gile[s] will calculate the
data when you render lightmaps etc. and save it to the exported file. 
; code by Beaker 2002 - please credit prominently (or arrange otherwise)



Function setup_example(mesh)
	zo.zorder = Zorderize(mesh)
End Function

Function mainloop_example(cam)
	For zo.zorder = Each zorder
		SortAlpha(zo,cam)
	Next
End Function



Type zorder
	Field hiddenmesh
	Field hiddensurf
	Field screenmesh
	Field screensurf
	Field x,y,z		;banks: size = tricnt * 2bytes(short)
	Field tricnt	;counttriangles(surf)-1
	Field incy		;use the y axis
End Type


Function Zorderize.zorder(mesh, incy = False)
	zo.zorder = New zorder
	zo\hiddenmesh = mesh
	zo\incy = incy

	zo\hiddensurf = GetSurface(zo\hiddenmesh,1)

	zo\tricnt = CountTriangles(zo\hiddensurf)-1
	zo\x = CreateBank(zo\tricnt*2+8)
	DebugLog BankSize(zo\x)
	If incy
		zo\y = CreateBank(zo\tricnt*2+8)
	EndIf
	zo\z = CreateBank(zo\tricnt*2+8)

	For f = 0 To zo\tricnt
		PokeShort zo\x, f*2, f
		If incy
			PokeShort zo\y, f*2, f
		EndIf
		PokeShort zo\z, f*2, f
	Next

	zo\screenmesh = CopyMesh(zo\hiddenmesh)
;	zo\screenmesh = CopyMesh(zo\hiddenmesh,getparent(zo\hiddenmesh))
	HideEntity zo\hiddenmesh
;	EntityFX zo\screenmesh,16

	zo\screensurf = GetSurface(zo\screenmesh,1)

	surf = zo\hiddensurf	;GetSurface(fullmesh,1)
	If Not surf Then RuntimeError "No surface found"
	ordered = False
	While ordered = False
		ordered = True
		For f = 1 To zo\tricnt
	;		If f > 0
				v0 = TriangleVertex ( surf,PeekShort(zo\x,f*2),0 )
				v1 = TriangleVertex ( surf,PeekShort(zo\x,f*2),1 )
				v2 = TriangleVertex ( surf,PeekShort(zo\x,f*2),2 )
				medx# = (VertexX(surf,v0)+VertexX(surf,v1)+VertexX(surf,v2)) / 3.0

				v0b = TriangleVertex ( surf,PeekShort(zo\x,(f-1)*2),0 )
				v1b = TriangleVertex ( surf,PeekShort(zo\x,(f-1)*2),1 )
				v2b = TriangleVertex ( surf,PeekShort(zo\x,(f-1)*2),2 )
				medxb# = (VertexX(surf,v0b)+VertexX(surf,v1b)+VertexX(surf,v2b)) / 3.0

				If (medx) > (medxb)
					temp = PeekShort(zo\x,f*2)
					PokeShort zo\x,f*2, PeekShort(zo\x,(f-1)*2)
					PokeShort zo\x, (f-1)*2, temp
					ordered = False
				EndIf


				v0 = TriangleVertex ( surf,PeekShort(zo\z,f*2),0 )
				v1 = TriangleVertex ( surf,PeekShort(zo\z,f*2),1 )
				v2 = TriangleVertex ( surf,PeekShort(zo\z,f*2),2 )

				medz# = (VertexZ(surf,v0)+VertexZ(surf,v1)+VertexZ(surf,v2)) / 3.0

				v0b = TriangleVertex ( surf,PeekShort(zo\z,(f-1)*2),0 )
				v1b = TriangleVertex ( surf,PeekShort(zo\z,(f-1)*2),1 )
				v2b = TriangleVertex ( surf,PeekShort(zo\z,(f-1)*2),2 )
				medzb# = (VertexZ(surf,v0b)+VertexZ(surf,v1b)+VertexZ(surf,v2b)) / 3.0

				If (medz) > (medzb)
					temp = PeekShort(zo\z,f*2)
					PokeShort zo\z,f*2, PeekShort(zo\z,(f-1)*2)
					PokeShort zo\z,(f-1)*2, temp
					ordered = False
				EndIf
	;		EndIf
		Next

		If incy
			For f = 1 To zo\tricnt
				v0 = TriangleVertex ( surf,PeekShort(zo\y,f*2),0 )
				v1 = TriangleVertex ( surf,PeekShort(zo\y,f*2),1 )
				v2 = TriangleVertex ( surf,PeekShort(zo\y,f*2),2 )
				medy# = (VertexX(surf,v0)+VertexX(surf,v1)+VertexX(surf,v2)) / 3.0

				v0b = TriangleVertex ( surf,PeekShort(zo\y,(f-1)*2),0 )
				v1b = TriangleVertex ( surf,PeekShort(zo\y,(f-1)*2),1 )
				v2b = TriangleVertex ( surf,PeekShort(zo\y,(f-1)*2),2 )
				medyb# = (VertexX(surf,v0b)+VertexX(surf,v1b)+VertexX(surf,v2b)) / 3.0

				If (medy) > (medyb)
					temp = PeekShort(zo\y,f*2)
					PokeShort zo\y,f*2, PeekShort(zo\y,(f-1)*2)
					PokeShort zo\y, (f-1)*2, temp
					ordered = False
				EndIf
			Next
		EndIf

		If KeyDown(1) Then End
	Wend

	Return zo
End Function


Function SortAlpha(zo.zorder,cam)
	Local origsurf = zo\hiddensurf
	Local newsurf = zo\screensurf
	Local xf,yf,zf,f
	TFormVector 0,0,1, cam,0
	If (Abs(TFormedX()) > Abs(TFormedZ())) And (Abs(TFormedX()) > Abs(TFormedY()))
		If prev <> 1
			prev = 1
			ClearSurface newsurf,0,1
			If TFormedX() > 0
				For f = 0 To zo\tricnt
					xf = PeekShort(zo\x,f*2)
					AddTriangle ( newsurf,TriangleVertex ( origsurf,xf,0 ),TriangleVertex ( origsurf,xf,1 ),TriangleVertex ( origsurf,xf,2 ) )
				Next
			Else
				For f = zo\tricnt To 0 Step -1
					xf = PeekShort(zo\x,f*2)
					AddTriangle ( newsurf,TriangleVertex ( origsurf,xf,0 ),TriangleVertex ( origsurf,xf,1 ),TriangleVertex ( origsurf,xf,2 ) )
				Next
			EndIf
		EndIf
	Else
		If (Abs(TFormedY()) > Abs(TFormedZ()))
			If (prev <> 2) And zo\incy
				prev = 2
				ClearSurface newsurf,0,1
				If TFormedY() > 0
					For f = 0 To zo\tricnt
						yf = PeekShort(zo\y,f*2)
						AddTriangle ( newsurf,TriangleVertex ( origsurf,yf,0 ),TriangleVertex ( origsurf,yf,1 ),TriangleVertex ( origsurf,yf,2 ) )
					Next
				Else
					For f = zo\tricnt To 0 Step -1
						yf = PeekShort(zo\y,f*2)
						AddTriangle ( newsurf,TriangleVertex ( origsurf,yf,0 ),TriangleVertex ( origsurf,yf,1 ),TriangleVertex ( origsurf,yf,2 ) )
					Next
				EndIf
			EndIf
		Else
			If prev <> 3
				prev = 3
				ClearSurface newsurf,0,1
				If TFormedZ() > 0
					For f = 0 To zo\tricnt
						zf = PeekShort(zo\z,f*2)
						AddTriangle ( newsurf,TriangleVertex ( origsurf,zf,0 ),TriangleVertex ( origsurf,zf,1 ),TriangleVertex ( origsurf,zf,2 ) )
					Next
				Else
					For f = zo\tricnt To 0 Step - 1
						zf = PeekShort(zo\z,f*2)
						AddTriangle ( newsurf,TriangleVertex ( origsurf,zf,0 ),TriangleVertex ( origsurf,zf,1 ),TriangleVertex ( origsurf,zf,2 ) )
					Next
				EndIf
			EndIf
		EndIf
	EndIf
End Function

Function FreeZorder()
	For zo.zorder = Each zorder
		FreeEntity zo\screenmesh 
		FreeBank zo\x 
		FreeBank zo\y 
		FreeBank zo\z 
	Next
	Delete Each zorder
End Function