C Library Functions - backface (3)
NAME
backface(3f) - [M_draw:POLYGONS] Turns on culling of backfacing polygons. (LICENSE:PD)
CONTENTS
Synopsis
Description
Examples
SYNOPSIS
subroutine backface(onoff)
logical onoff
DESCRIPTION
Turns on culling of backfacing polygons. A polygon is backfacing if its orientation in *screen* coords is clockwise, unless a call to backfacedir is made.
EXAMPLES
Sample program:
program demo_backface ! demonstrate double buffering and what happens ! when you hit clipping plane ! ! Specifying an extra argument turns on the polygon filling. ! use M_draw implicit none character(len=30) :: device character(len=1) :: c real r, t, dr, dt integer nplanes logical fill, back, backdir integer :: ios integer :: ipaws!print*,’Enter output device:’ read(*,’(a)’,iostat=ios)device if(ios.ne.0)device=’ ’
dr = 0.3 dt = 0.2 print*,’Enter delta in degrees (0.333 is typical):’ read(*,*,iostat=ios) dr if(ios.ne.0)dr=0.333 write(*,*)’DR=’,dr
call prefsize(300, 300)
call vinit(device)
nplanes = getdepth()
fill = .true. back = .true. backdir = .true.
call polyfill(fill) call backface(back) call backfacedir(backdir)
call color(D_BLACK) call clear()
call window(-1.5, 1.5, -1.5, 1.5, 9.0, -5.0) call lookat(0.0, 0.0, 12.0, 0.0, 0.0, 0.0, 0.0)
t = 0.0 r = 30.0 ! ! Setup drawing into the backbuffer.... ! if (backbuffer().lt.0) then write(*,*)’Device can’’t support doublebuffering’ ! draw a single view so at least the cube is displayed call frontbuffer() call color(D_BLACK) call clear() call translate(0.0, 0.0, t) call rotate(r, ’y’) call rotate(r, ’z’) call rotate(r, ’x’) call color(D_WHITE) call polyfill(.true.) call drawcube(nplanes) call color(D_BLACK) call polyfill(.false.) call drawcube(nplanes) ipaws=getkey() call vexit() stop
endif
do if(r.ge.360) r = 0.0 call color(D_BLACK) call clear()
call pushmatrix()
call translate(0.0, 0.0, t) call rotate(r, ’y’) call rotate(r, ’z’) call rotate(r, ’x’) call color(D_WHITE)
call drawcube(nplanes)
if (nplanes .eq. 1 .and. fill) then call polyfill(.false.) call color(D_BLACK) call drawcube(nplanes) call polyfill(fill) endif
call popmatrix()
t = t + dt if (t.gt.3.0 .or. t.lt.-18.0) dt = -dt
call swapbuffers()
c = char(checkkey()) if (c .eq. ’f’) then fill = .not. fill call polyfill(fill) elseif (c .eq. ’b’) then back = .not. back call backface(back) elseif (c .eq. ’d’) then backdir = .not. backdir call backfacedir(backdir) elseif (c .ne. char(0)) then call vexit() stop endif
r = r + dr enddo
contains ! this routine draws the cube, using colours if available ! subroutine drawcube(nplanes) integer nplanes
real carray(3, 8) data carray/ & & -1.0, -1.0, 1.0, & & 1.0, -1.0, 1.0, & & 1.0, 1.0, 1.0, & & -1.0, 1.0, 1.0, & & -1.0, -1.0, -1.0, & & 1.0, -1.0, -1.0, & & 1.0, 1.0, -1.0, & & -1.0, 1.0, -1.0/ save carray
if (nplanes.gt.1) call color(D_RED)
call makepoly() call move(carray(1,1), carray(2,1), carray(3,1)) call draw(carray(1,2), carray(2,2), carray(3,2)) call draw(carray(1,3), carray(2,3), carray(3,3)) call draw(carray(1,4), carray(2,4), carray(3,4)) call draw(carray(1,1), carray(2,1), carray(3,1)) call closepoly()
if (nplanes.gt.1) call color(D_GREEN)
call makepoly() call move(carray(1,6), carray(2,6), carray(3,6)) call draw(carray(1,5), carray(2,5), carray(3,5)) call draw(carray(1,8), carray(2,8), carray(3,8)) call draw(carray(1,7), carray(2,7), carray(3,7)) call draw(carray(1,6), carray(2,6), carray(3,6)) call closepoly()
if (nplanes.gt.1) call color(D_YELLOW)
call makepoly() call move(carray(1,2), carray(2,2), carray(3,2)) call draw(carray(1,6), carray(2,6), carray(3,6)) call draw(carray(1,7), carray(2,7), carray(3,7)) call draw(carray(1,3), carray(2,3), carray(3,3)) call draw(carray(1,2), carray(2,2), carray(3,2)) call closepoly()
if (nplanes.gt.1) call color(D_BLUE)
call makepoly() call move(carray(1,1), carray(2,1), carray(3,1)) call draw(carray(1,4), carray(2,4), carray(3,4)) call draw(carray(1,8), carray(2,8), carray(3,8)) call draw(carray(1,5), carray(2,5), carray(3,5)) call draw(carray(1,1), carray(2,1), carray(3,1)) call closepoly()
if (nplanes.gt.1) call color(D_MAGENTA)
call makepoly() call move(carray(1,3), carray(2,3), carray(3,3)) call draw(carray(1,7), carray(2,7), carray(3,7)) call draw(carray(1,8), carray(2,8), carray(3,8)) call draw(carray(1,4), carray(2,4), carray(3,4)) call draw(carray(1,3), carray(2,3), carray(3,3)) call closepoly()
if (nplanes.gt.1) call color(D_CYAN)
call makepoly() call move(carray(1,1), carray(2,1), carray(3,1)) call draw(carray(1,5), carray(2,5), carray(3,5)) call draw(carray(1,6), carray(2,6), carray(3,6)) call draw(carray(1,2), carray(2,2), carray(3,2)) call draw(carray(1,1), carray(2,1), carray(3,1)) call closepoly()
end subroutine drawcube
end program demo_backface
| Nemo Release 3.1 | backface (3) | February 23, 2025 |
