Code archives/3D Graphics - Mesh/TriSteepness

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TriSteepness by ringwraith
(Posted 19 years ago)
This is a method of calculating the steepness (gradient) of a triangle by finding the slope of the edges of the triangle and returning the steepest one. It is substantially faster than a more complex method which I was using for a while that was posted in these archives. This takes about 0 - 1 milliseconds compared to 30 - 35 milliseconds using the more complex function. Of course, for the speed, some accuracy is sacrificed, but it is usually very accurate and the most I have seen it vary from the results of the more complex version is by about 0.07.
Note: If the triangle is vertical this function will not work. 
Function TriSteepness#(surface,index)

	vert0 = TriangleVertex(surface,index,0)
	vert1 = TriangleVertex(surface,index,1)
	vert2 = TriangleVertex(surface,index,2)
	vert0to1# = VertSteepness#(surface,TriangleVertex(surface,index,0),surface,TriangleVertex(surface,index,1))
	vert0to2# = VertSteepness(surface,TriangleVertex(surface,index,0),surface,TriangleVertex(surface,index,2))
	vert1to2# = VertSteepness#(surface,TriangleVertex(surface,index,1),surface,TriangleVertex(surface,index,2))
	If vert0to1# => vert0to2# And vert0to1# => vert1to2# Then Return vert0to1#
	If vert0to2# => vert0to1# And vert0to2# => vert1to2# Then Return vert0to2#
	If vert1to2# => vert0to2# And vert1to2# => vert0to1# Then Return vert1to2#
	
End Function 

Function VertDist#(surface,index,x#,Z#)

	xdist# = VertexX(surface,index) - x
	Zdist# = VertexZ(surface,index) - Z
	
	Dist# = Sqr(Xdist^2 + Zdist^2)
	
	Return Dist#
	
End Function

Function VertSteepness#(surface,index,surface2,index2)

	vertgroundist# = VertDist#(surface,index,VertexX(surface2,index2),VertexZ(surface2,index2))
	vertupdist# = Abs(VertexY(surface2,index2) - VertexY(surface,index))
	slope# = vertupdist#/vertgroundist#
 
	Return slope#
	
End Function

Comments

Stevie G
(Posted 19 years ago)
Better and quicker just to calculate the triangle Y normal component, rather than the steepest edge, like so ...

Where >0 = Flat up , <0 = flat down, 0 = steepest / vertical

Function TriangleNY#( s , t )

	v0 = TriangleVertex( s, t, 0 )
	v1 = TriangleVertex( s, t, 1 )
	v2 = TriangleVertex( s, t, 2 )
	ax# = VertexX( s, v1 ) - VertexX( s, v0 )
	ay# = VertexY( s, v1 ) - VertexY( s, v0 )	
	az# = VertexZ( s, v1 ) - VertexZ( s, v0 )	
	bx# = VertexX( s, v2 ) - VertexX( s, v1 )
	by# = VertexY( s, v2 ) - VertexY( s, v1 )	
	bz# = VertexZ( s, v2 ) - VertexZ( s, v1 )	
	Nx# = ( ay * bz ) - ( az * by )
	Ny# = ( az * bx ) - ( ax * bz )
	Nz# = ( ax * by ) - ( ay * bx )
	Ns# = Sqr( Nx * Nx + Ny * Ny + Nz * Nz )
       
        if Ns > 0
   
	   Return Ny / Ns

        else

           return 0

        endif

End Function


Stevie

ringwraith
(Posted 19 years ago)
Oh cool, you learn something new everyday!

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