SUBROUTINE CWTV
C
C     NAME: CWTV
C
C    LANGUAGE:  FORTRAN
C
C    OPERATING SYSTEM:  UNIVERSAL
C
C    ORDER NUMBER:  5428-SE
C
C    PART NUMBER:  000-026366  NOVEMBER 1985
C
C    PRODUCT:  UNIVERSAL VERSAPLOT COLOR RANDOM 2.0
C
C    VERSATEC, INC., SANTA CLARA, CALIFORNIA 95051
C    A XEROX COMPANY
C
C    Copyright (C) 1985 by Xerox Corporation.  All rights reserved.
C
C    "NOTICE. THIS PROGRAM IS THE EXCLUSIVE PROPERTY OF VERSATEC,
C    INC. AND IS ISSUED IN STRICT CONFIDENCE UNDER A PREARRANGED
C    LICENSE AGREEMENT AND IS NOT TO BE DISCLOSED IN ANY MANNER TO
C    PERSONS OUTSIDE THE LICENSED ORGANIZATION AND SHALL NOT BE
C    REPRODUCED OR DISSEMINATED, IN WHOLE OR PART, TO ANYONE OUTSIDE
C    THE LICENSED ORGANIZATION WITHOUT THE PRIOR WRITTEN APPROVAL OF
C    VERSATEC, INC. UNLESS OTHERWISE PROVIDED FOR BY SUCH LICENSE
C    AGREEMENT.  THIS WORK IS PROTECTED AS AN UNPUBLISHED WORK UNDER
C    THE COPYRIGHT ACT OF 1976."
C
C     CWTV - CALCULATE WINDOW TRANSFORMATION VARIABLES
C
C     CWTV IS CALLED BY VPORT, WINDOW, AND FACTOR TO RECALCULATE THE
C     WINDOW TRANFORMATION WHENEVER THE WINDOW OR VIEWPORT IS CHANGED.
C     CWTV ALSO UPDATES COMMON VARIABLES XDOTS AND YDOTS.
C
C
C     THE WINDOW TO VIEWPORT TRANSFORMATION USED IS DESCRIBED IN
C     SECTION 5-6 OF "PRINCIPALS OF INTERACTIVE COMPUTER GRAPHICS",
C     MCGRAW HILL, 1979, BY NEWMAN AND SPROULL.
C
C     GIVEN A VIRTUAL PLOTTING WINDOW DESCRIBED BY WXMIN,WYMIN,WXMAX,
C     WYMAX, AND A VIEWPORT DESCRIBED BY VXMIN,VYMIN,VXMAX,VYMAX,
C     WHICH SPECIFIES IN DEVICE COORDINATES THE AREA ON THE PLOTTER
C     TO WHICH THE WINDOW WILL BE MAPPED, POINT (X,Y) IN THE WINDOW
C     COORDINATE SYSTEM MAPS TO POINT (IX',IY') IN THE DEVICE
C     COORDINATE SYSTEM ACCORDING TO THE FOLLOWING EQUATION:
C
C       IX'=((VXMAX-VXMIN)/(WXMAX-WXMIN)*(X-WXMIN)+VXMIN)*XDEN + 0.5
C       IY'=((VYMAX-VYMIN)/(WYMAX-WYMIN)*(Y-WYMIN)+VYMIN)*YDEN + 0.5
C
C       THESE EQUATIONS CAN BE SIMPLIFIED TO THE FORM:
C
C         IX' = A*X + B
C         IY' = C*Y + D
C
C       THE VARIABLES A,B,C,D CORRESPOND TO WTV(1),WTV(2),WTV(3),
C       WTV(4) AND ARE USED IN SUBROUTINES PLOT AND TONE.
C
C     ENTRY:  CALL CWTV
C
C     EXIT:  COMMON VARIABLES WTV(),XDOTS, AND YDOTS HAVE
C            BEEN RECALCULATED
C
C     CALLS: NONE
C
C     CALLED BY: VPORT,WINDOW
C
C     COMMON USED:
C     /DVCOM/
C            I ANC     - HOLD PREVIOUS SYMBOL CALL ANGLE VALUE
C            I HTC     - HOLD PREVIOUS SYMBOL CALL HEIGHT VALUE
C            I ICWTV   - SUBROUTINE CWTV FIRST CALL FLAG
C            R WTV()   - WINDOW TRANSFORMATION VARIABLES. USED TO
C                        TRANSFORM COORDINATES FROM THE VIEW WINDOW
C                        SYSTEM TO THE  VIEWPORT SYSTEM
C            R XDEN    - NUMBER OF NIBS PER VIEWPORT UNIT IN THE X
C                        DIRECTION
C            R YDEN    - THE NUMBER OF NIBS PER VIEWPORT UNIT IN
C                        THE Y DIRECTION.
C
C     LOCAL:  NONE
C
C
C
      LOGICAL ROT90,PMOVE,IPDEF,DASHPN,XMAJOR,VSFLAG
      INTEGER PWIDTH,XNIPS,YNIPS,PENPAT,VSMAX,PFONT
C...  COMMON /DVCOM/  PHASE I COMMON VARIABLES
C
      COMMON /DVCOM/
     *         ANC,    DASHPN, FACT,   HTC,    ICUT,   ICWTV,  ICXPTS,
     *         IEOJ,   ILWM,   ILWP,   IOPEN,  ISORT,  ITFLAG, IX1,
     *         IX2,    IY1,    IY2,    JFONT,  JPEN,   KPAT,   KWIDTH,
     *         LASTX,  LASTY,  MAXPAT, MSB,    MSKALL, NCH,    NCLIP,
     *         NIBSX,  NLPAT,  NPLOT,  PFONT,  PMOVE,  PXMIN,  PXMAX,
     *         PYMIN,  PYMAX,  RADN,   ROT90,  SXC,    SYC,    TSINA,
     *         TCOSA,  XDEN,   XFAC,   XNIPS,  XOFF,   YDEN,   YFAC,
     *         YOFF,   YNIPS,  VSFLAG, VSMAX,  XMAJOR,
     *         IPAT(16,256), IEOP(4),  IHBUF(2), IPDEF(64),
     *         NPAT(255),    PENPAT(4,64), PWIDTH(64),
     *         RORG(2), VCP(2), VP(4), WIN(4), WTV(4), WX(4),  WY(4),
     *         IAUTXT(15)
C
C
C
C...  RETURN ON FIRST CALL TO AVOID A DIVIDE BY 0.
      IF (ICWTV .NE. 0) GO TO 10
         ICWTV = -1
         GO TO 999
C
C...  COMPUTE WINDOW TRANSFORMATION VARIABLES
   10 WTV(1)=XDEN*((VP(3)-VP(1))/(WIN(3)-WIN(1)))
      WTV(2)=XDEN*VP(1) - WTV(1)*WIN(1) + .5
      WTV(3)=YDEN*((VP(4)-VP(2))/(WIN(4)-WIN(2)))
      WTV(4)=YDEN*VP(2) - WTV(3)*WIN(2) + .5
C
C...  RESET PREVIOUS ANGLE/HEIGHT
      ANC = 0.0
      HTC = 0.0
C
C
  999 RETURN
      END