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PROGRAM PGDEM7
C
C Demonstration program for 3D surface plotting routine FREDDY.
C
INTEGER PGBEG
REAL A(51,51), R, SIZE
INTEGER I, J
C
IF (PGBEG(0, '?', 1, 1) .NE. 1) THEN
STOP
END IF
C
C Calculate a sample data array.
C
DO 20 I=1,51
DO 10 J=1,51
R = (I-26)**2 + (J-26)**2
R = 0.5*SQRT(R)
IF (R.GT.0.0) THEN
A(I,J) = SIN(R)/R
ELSE
A(I,J) = 1.0
END IF
10 CONTINUE
20 CONTINUE
C
C FREDDY assumes the window is square of size SIZE.
C
SIZE = 1.0
CALL PGENV(0., SIZE, 0., SIZE, 1, -2)
CALL FREDDY(A,51,51, SIZE, 25.0)
CALL PGEND
END
C-----------------------------------------------------------------------
SUBROUTINE FREDDY(ARRAY,KX,NY,SIZE,ANGLE)
INTEGER KX, NY
REAL ARRAY(KX,NY), SIZE, ANGLE
C
C Draws isometric plot of array
C
REAL FMAX,FMIN,DELTAX,DELTAY,DELTAV,SINE,PEAK,X,DX,HEIGHT
INTEGER I,J,KI,KJ,NX,MX,MY,STEP,LEFT,RIGHT,IT,MN,INCX
LOGICAL VISBLE
COMMON /FREDCM/ DELTAX,X,STEP,LEFT,RIGHT,IT,NX,VISBLE
C
MN = KX*NY
NX = KX
C Check array size:
IF(NX.LT.2 .OR. NY.LT.2) RETURN
FMAX = ARRAY(1,1)
FMIN = FMAX
DO 20 J=1,NY
DO 10 I=1,NX
FMIN = AMIN1(ARRAY(I,J),FMIN)
FMAX = AMAX1(ARRAY(I,J),FMAX)
10 CONTINUE
20 CONTINUE
DELTAX = SIZE/(NX+NY)
SINE = SIN(ANGLE/58.)
DELTAY = DELTAX*SINE
HEIGHT = SIZE*(1.-ABS(SINE))
DELTAV = HEIGHT
FMAX = FMAX-FMIN
IF(FMAX.LT.0.0001) FMAX = DELTAV
DELTAV = DELTAV/FMAX
MX = NX+1
MY = NY+1
STEP = MX
C
C Start PGPLOT buffering.
C
CALL PGBBUF
C
C Work our way down the Y axis, then up the X axis,
C calculating the Y plotter coordinates for each
C column of the plot, doing the hidden-line suppression
C at the same time.
C
DO 50 J=1,NY
KJ = MY-J
KI = 1
C ( KI,KJ are coordinates of bottom of column)
ARRAY(KI,KJ) = DELTAY*(KI+KJ) + DELTAV*(ARRAY(KI,KJ)-FMIN)
30 PEAK = ARRAY(KI,KJ)
40 KI = KI+1
KJ = KJ+1
IF(KI.GT.NX .OR. KJ.GT.NY) GOTO 50
ARRAY(KI,KJ) = DELTAY*(KI+KJ) + DELTAV*(ARRAY(KI,KJ)-FMIN)
IF(ARRAY(KI,KJ).GT.PEAK) GOTO 30
IF(ARRAY(KI,KJ).LE.PEAK) ARRAY(KI,KJ) = -ABS(ARRAY(KI,KJ))
GOTO 40
50 CONTINUE
C
C Now to work our way up the X axis
C
DO 80 I=2,NX
KI = I
KJ = 1
ARRAY(KI,KJ) = DELTAY*(KI+KJ)+DELTAV*(ARRAY(KI,KJ)-FMIN)
60 PEAK = ARRAY(KI,KJ)
70 KI = KI+1
KJ = KJ+1
IF(KI.GT.NX .OR. KJ.GT.NY) GOTO 80
ARRAY(KI,KJ) = DELTAY*(KI+KJ)+DELTAV*(ARRAY(KI,KJ)-FMIN)
IF(ARRAY(KI,KJ).GT.PEAK) GOTO 60
IF(ARRAY(KI,KJ).LE.PEAK) ARRAY(KI,KJ) = -ABS(ARRAY(KI,KJ))
GOTO 70
80 CONTINUE
C
C Draw a line along the bottom of the vertical faces
C
CALL PGMOVE(DELTAX*(NX+NY-2), DELTAY*(MX))
CALL PGDRAW(DELTAX*(NY-1), DELTAY*2)
CALL PGDRAW(0.0, DELTAY*MY)
C
C Array is now ready for plotting. If a point is
C positive, then it is to be plotted at that Y
C coordinate; if it is negative, then it is
C invisible, but at minus that Y coordinate (the point
C where the line heading towards it disappears has to
C be determined by finding the intersection of it and
C the cresting line).
C
C Plot rows:
C
DO 110 J=1,NY,2
KJ = MY-J
DX = DELTAX*(J-2)
X = DX+DELTAX
CALL PGMOVE(X,DELTAY*(KJ+1))
CALL PGDRAW(X,ARRAY(1,KJ))
VISBLE = .TRUE.
DO 90 I=2,NX
RIGHT = I+NX*(KJ-1)
LEFT = RIGHT-1
IT = RIGHT
X = DX+DELTAX*I
CALL FREDGO(ARRAY,MN)
90 CONTINUE
C
C Now at far end of row so come back
C
KJ = KJ-1
IF(KJ.LE.0) GOTO 170
VISBLE = ARRAY(NX,KJ).GE.0.0
DX = DELTAX*(NX+J)
IF(VISBLE) CALL PGMOVE(DX-DELTAX,ARRAY(NX,KJ))
DELTAX = -DELTAX
DO 100 I=2,NX
KI = MX-I
LEFT = KI+NX*(KJ-1)
RIGHT = LEFT+1
IT = LEFT
X = DX+DELTAX*I
CALL FREDGO(ARRAY,MN)
100 CONTINUE
C
X = DX+DELTAX*NX
IF(.NOT.VISBLE) CALL PGMOVE(X,ARRAY(1,KJ))
CALL PGDRAW(X,DELTAY*(KJ+1))
C (set DELTAX positive for return trip)
DELTAX = -DELTAX
110 CONTINUE
C
C Now do the columns:
C as we fell out of the last DO-loop we do the
C columns in ascending-X order
C
INCX = 1
KI = 1
C (set DELTAX -ve since scanning R to L)
120 DX = DELTAX*(KI+NY-1)
DELTAX = -DELTAX
X = DX+DELTAX
CALL PGMOVE(X,ARRAY(1,1))
130 VISBLE = .TRUE.
DO 140 J=2,NY
LEFT = KI+NX*(J-1)
RIGHT = LEFT-NX
IT = LEFT
X = DX+DELTAX*J
CALL FREDGO(ARRAY,MN)
140 CONTINUE
C
C At far end, increment X and check still inside array
C
KI = KI+INCX
IF(KI.LE.0 .OR. KI.GT.NX) GOTO 180
VISBLE = ARRAY(KI,NY).GE.0.0
DELTAX = -DELTAX
DX = DELTAX*(KI-2)
X = DX+DELTAX
IF(VISBLE) CALL PGMOVE(X,ARRAY(KI,NY))
DO 150 J=2,NY
KJ = MY-J
RIGHT = KI+NX*(KJ-1)
LEFT = RIGHT+NX
IT = RIGHT
X = DX+DELTAX*J
CALL FREDGO(ARRAY,MN)
150 CONTINUE
C
X = DX+DELTAX*NY
IF(.NOT.VISBLE) CALL PGMOVE(X,ARRAY(KI,1))
IF(KI.EQ.1) GOTO 180
CALL PGDRAW(X,DELTAY*(KI+1))
KI = KI+INCX
IF(KI.GT.NX) GOTO 180
IF(KI.EQ.1) GOTO 120
160 DELTAX = -DELTAX
DX = DELTAX*(1-KI-NY)
X = DX+DELTAX
CALL PGMOVE(X,DELTAY*(KI+1))
CALL PGDRAW(X,ARRAY(KI,1))
GOTO 130
C
C Do columns backwards because ended rows at far end of X
C
170 KI = NX
INCX = -1
DX = DELTAX*(KI+NY)
GOTO 160
C
C
180 CALL PGEBUF
END
C-----------------------------------------------------------------------
SUBROUTINE FREDGO(ARRAY,MN)
INTEGER MN
REAL ARRAY(MN)
C
INTEGER STEP,LEFT,RIGHT,IT,NX
LOGICAL VISBLE
REAL AL,AR,BL,EM,XX,X,Y,DELTAX
COMMON /FREDCM/ DELTAX,X,STEP,LEFT,RIGHT,IT,NX,VISBLE
C
C Test visibility
C
IF(ARRAY(IT).LT.0.0) GOTO 80
C
C This point is visible - was last?
C
IF(VISBLE) GOTO 50
C
C No: calculate point where this line vanishes
C
10 IF(LEFT.LE.NX .OR. MOD(LEFT-1,NX).EQ.0 .OR.
1 RIGHT.LE.NX .OR. MOD(RIGHT-1,NX).EQ.0) GOTO 100
AL = ABS(ARRAY(LEFT))
AR = ABS(ARRAY(RIGHT))
IF(ARRAY(LEFT).LT.0.0) GOTO 70
C Right-hand point is crested
20 RIGHT = RIGHT-STEP
IF(ARRAY(RIGHT).LT.0.0) GOTO 20
C Left-hand end of cresting line is either
C RIGHT+NX or RIGHT-1
LEFT = RIGHT+NX
IF(ARRAY(LEFT).LT.0.0) LEFT = RIGHT-1
C
C RIGHT and LEFT index into the endpoints of the
C cresting line
30 BL = ABS(ARRAY(LEFT))
EM = ABS(ARRAY(RIGHT))-BL
XX = EM-AR+AL
IF(ABS(XX).LT.0.0001) GOTO 60
XX = (AL-BL)/XX
40 Y = EM*XX+BL
IF(DELTAX.GT.0.0) XX = 1.0-XX
XX = X-XX*DELTAX
IF(VISBLE) GOTO 90
C Drawing a line from an invisible point
C to a visible one
CALL PGMOVE(XX,Y)
VISBLE = .TRUE.
50 CALL PGDRAW(X,ARRAY(IT))
RETURN
C
60 XX = 0.5
GOTO 40
C
C Left-hand point crested
C
70 LEFT = LEFT-STEP
IF(ARRAY(LEFT).LT.0.0) GOTO 70
C
C Right-hand end of cresting line is either LEFT+1 or LEFT-NX
C
RIGHT = LEFT+1
IF(ARRAY(RIGHT).LT.0.0) RIGHT = LEFT-NX
GOTO 30
C
C This point is invisible; if last one was too, then forget it;
C else draw a line towards it
C
80 IF(.NOT.VISBLE) RETURN
GOTO 10
C
90 CALL PGDRAW(XX,Y)
100 VISBLE = .FALSE.
RETURN
END
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