Some help for you-find face normal function

GLGraphics 640,480
glEnable GL_DEPTH_TEST								'Enables Depth Testing
glEnable GL_LIGHTING
glEnable GL_LIGHT0
glMatrixMode GL_PROJECTION							'Select The Projection Matrix
glLoadIdentity										'Reset The Projection Matrix

glFrustum -0.1, 0.1,-0.1, 0.1, 0.1, 100.0				'Setup The Projection Matrix Frustum

glMatrixMode GL_MODELVIEW							'Select The ModelView Matrix
glLoadIdentity										'Reset The ModelView Matrix
Local rquad:Float

Type surface_normal
Field x:Float, y:Float, z:Float
 
EndType ' something to hold data for surface normal
Function create_surface_normal:surface_normal(p1x:Float, p1y:Float, p1z:Float, p2x:Float, p2y:Float, p2z:Float, p3x:Float, p3y:Float, p3z:Float, bool_side = 0) 
		Local nx:Float = ((p3y - p2y) * (p2z - p1z)) - ((p3z - p2z) * (p2y - p1y)) 
		Local ny:Float = ((p3z - p2z) * (p2x - p1x)) - ((p3x - p2x) * (p2z - p1z)) 
		Local nz:Float = ((p3x - p2x) * (p2y - p1y)) - ((p3y - p2y) * (p2x - p1x)) 
		Local N:Float = Sqr((nx * nx) + (ny * ny) + (nz * nz)) 
			
			If bool_side = 1
				N = n * -1.0
			EndIf
			
		Local a:Float = (1.0 / N) * nx
		Local b:Float = (1.0 / N) * ny
		Local c:Float = (1.0 / N) * nz
		Local v:surface_normal = New surface_normal
		
		v.x = a
		v.y = b
		v.z = c
		Return v
endfunction 
									

While Not KeyHit( KEY_ESCAPE )

	glClear GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT		'Clear The Screen And The Depth Buffer
					'Rotate The Triangle On The Y axis ( New )

	
	glLoadIdentity()								'Reset The Current Modelview Matrix
	glTranslatef 0.0, 0.0, - 1.0						'Move Right 1.5 Units and Into The Screen 7.0
	glRotatef rquad, 1.0, 1.0, 0.0						'Rotate The Quad On The X, Y and Z axis ( New )
	
	
	' note: lights disable glcolor3f() so we must use glmaterial instead
	Local mcolor:Float[]=[0.0, 0.3, 1.0, 1.0] ' set an array for a nice blue color
	glMaterialfv(GL_FRONT, GL_AMBIENT, mcolor)     ' Set the material from the array as the Current material
	Local diffuse:Float[]=[1.0, 0.0, 1.0, 1.0]
	glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuse) 
	Local specular:Float[]=[0.0, 0.3, 1.0, 1.0]
	glMaterialfv(GL_FRONT, GL_SPECULAR, specular) 
	glMateriali(GL_FRONT, GL_SHININESS, 128) 
	
	

	glBegin(GL_TRIANGLES) 
	
		Local v:surface_normal = New surface_normal ' just Save a vertex To compute Values
		Local topy:Float = -.5 ' the y coordinate of the top point
		Local bottomy:Float =.5 ' the y coordinate of the bottom point
		Local centery:Float = 0.0 ' this is the coordinate For the y of the origen
		Local centerx:Float = 0.0 'this is the coordinate For x at the origen or 0
		Local centerz:Float = 0.0 ' this is the coordinate For z at the origen
		
		For Local i = 0 To 35
			Local currentx:Float = Cos(i * 10.0) *.5 ' current value of x at i
			Local currentz:Float = Sin(i * 10.0) *.5 ' current value of z at i
			Local oldx:Float = Cos((i - 1) * 10.0) *.5 ' previous value of x at i
			Local oldz:Float = Sin((i - 1) * 10.0) *.5 ' previous value of z at i
			' this is the top trianle belt "winding" the vertices in this direction
			' means that we must set the last parameter of "create_surface_normal" to 0
			v = create_surface_normal(centerx, topy, centerz, currentx, centery, currentz, oldx, centery, oldz, 0) 
			glNormal3f(v.x, v.y, v.z) 
			glColor3f(1.0, 0.0, 0.0) 
			glVertex3f(centerx, topy, centerz) 
			glVertex3f(currentx, centery, currentz) 
			glVertex3f(oldx, centery, oldz) 
			
			' this is the bottom belt this time we wind the triangle verticies in the opposite direction
			' so "bool_side" must be 1 instead of 0
			v = create_surface_normal(currentx, centery, currentz, oldx, centery, oldz, centerx, bottomy, centerz, 1) 
			glNormal3f(v.x, v.y, v.z) 
			glColor3f(0.0, 0.0, 1.0) 
			glVertex3f(currentx, centery, currentz) 
			glVertex3f(oldx, centery, oldz) 
			glVertex3f(centerx, bottomy, centerz) 
		Next
	glEnd										'Finished Drawing The Box										'Increase The Rotation Variable For The Triangle ( New )
	rquad:-0.85									'Decrease The Rotation Variable For The Quad     ( New )

	Flip

Wend