'===========================================================================
' Subject: 3D SURFACE PLOT                   Date: 12-14-98 (14:35)       
' Author:  Dave Navarro, Jr.                 Code: PB                     
' Origin:  dave@powerbasic.com             Packet: GRAPHICS.ABC
'===========================================================================
'3D Surface plot
'From "Microcomputer Graphics Techniques and Applications" by Donald Hearn
'Ported to PB by Dave Navarro (dave@powerbasic.com)

$LIB GRAPH ON

SCREEN 12

WINDOW (-4, -3) - (4, 3)

RHO = 50 '30
D = 10

THETA = 1
S1 = SIN(THETA)
C1 = COS(THETA)

PHI = 1
S2 = SIN(PHI)
C2 = COS(PHI)

FOR x = 15 TO -15 STEP -.5
 FL = 0
 FOR Y = -10 TO 10
   Z = F(x,y)
   XE = -X*S1 + Y*C1
   YE = -X*C1*C2 - Y*S1*C2 + Z*S2
   ZE = -X*S2*C1 - Y*S1*S2 - Z*C2 + RHO
   SX = D*XE/ZE
   SY = D*YE/ZE
   IF FL = 0 THEN
     FL = 1
     PSET (SX, SY), 2
   END IF
   LINE - (SX, SY), 2
 NEXT Y
NEXT x

SLEEP
SCREEN 0, 0, 0

FUNCTION F(x, y)
  FUNCTION = 3*COS(.05*(X*X + Y*Y))
END FUNCTION