Manual Reference Pages - lookat (3)
NAME
lookat(3f) - [M_draw:VIEWPORT] Specify the viewer’s position (LICENSE:PD)
CONTENTS
Synopsis
Description
Example
SYNOPSIS
subroutine lookat(vx, vy, vz, px, py, pz, twist) real vx, vy, vz, px, py, pz, twist
DESCRIPTION
Specify the viewer’s position by giving a viewpoint and a reference point in world coordinates. A twist about the line of sight may also be given.
EXAMPLE
Sample program:
program demo_lookat ! Demonstrate a rotating translating tetrahedron, and doublebuffering use M_draw use M_time, only : system_sleep ! integer TETRAHEDRON parameter (TETRAHEDRON = 1) ! real R, tx, tz, rotval, drotval, zeye integer i logical back, backdir, fill character(len=50) :: device integer :: ios ! call prefsize(300, 300) ! print*,’Enter output device:’ read(*,’(a)’,iostat=ios)device if(ios.ne.0)device=’ ’ ! back = .true. backdir = .true. fill = .true. ! call vinit(device) ! ! Make the tetrahedral object ! call maketheobject() ! rotval = 0.0 drotval = 5.0 zeye = 5.0 ! R = 1.6 ! tx = 0.0 tz = R ! !all polyfill(fill) call backface(back) call backfacedir(backdir) call clipping(.false.) ! ! set up a perspective projection with a field of view of ! 40.0 degrees, aspect ratio of 1.0, near clipping plane 0.1, ! and the far clipping plane at 1000.0. ! call perspective(40.0, 1.0, 0.001, 15.0) call lookat(0.0, 0.0, zeye, 0.0, 0.0, 0.0, 0.0) ! ! Setup drawing into the backbuffer.... ! if (backbuffer().lt.0) then call vexit() write(*,*)’Device can’’t support doublebuffering’ stop endif ! ! we loop back here ad-naseum until someone hits a non-interpreted key ! INFINITE: do ! rotval = 0.0 ! do i = 0, int(359.0 / drotval) ! call color(D_BLACK) call clear() ! ! Rotate the whole scene...(this accumulates - hence ! drotval) ! call rotate(drotval * 0.1, ’x’) call rotate(drotval * 0.1, ’z’) ! call color(D_RED) call pushmatrix() call polyfill(.false.) call rotate(90.0, ’x’) call circle(0.0, 0.0, R) call polyfill(fill) call popmatrix() ! call color(D_BLUE) call move(0.0, 0.0, 0.0) call draw(tx, 0.0, tz) ! ! Remember! The order of the transformations is ! the reverse of what is specified here in between ! the pushmatrix and the popmatrix. These ones don’t ! accumulate because of the push and pop. ! call pushmatrix() call translate(tx, 0.0, tz) call rotate(rotval, ’x’) call rotate(rotval, ’y’) call rotate(rotval, ’z’) call scale(0.4, 0.4, 0.4) call callobj(TETRAHEDRON) call popmatrix() ! tz = R * cos(rotval * 3.1415926535 / 180) tx = R * sin(rotval * 3.1415926535 / 180) ! call swapbuffers() ! select case(char(checkkey())) case(’f’) fill = .not. fill call polyfill(fill) case(’b’) back = .not. back call backface(back) case(’d’) backdir = .not. backdir call backfacedir(backdir) case(char(0)) case default call vexit() stop end select ! rotval = rotval + drotval ! call system_sleep(0.05) ! enddo ! enddo INFINITE ! contains ! ! maketheobject ! ! generate a tetrahedron object as a series of move draws ! subroutine maketheobject()integer TETRAHEDRON, NSIDES, NFACES, NPNTS parameter (TETRAHEDRON = 1, NSIDES = 3, NFACES = 4, NPNTS = 4) integer colface(NFACES) real pnts(3, NPNTS) integer faces(NSIDES, NFACES) integer i, j real x, y, z
data pnts/ & & -0.5, 0.866, -0.667, & & -0.5, -0.866, -0.667, & & 1.0, 0.0, -0.667, & & 0.0, 0.0, 1.334/
data colface/D_GREEN, D_YELLOW, D_CYAN, D_MAGENTA/
data faces/ & & 3, 2, 1, & & 1, 2, 4, & & 2, 3, 4, & & 3, 1, 4/
call makeobj(TETRAHEDRON)
do i = 1, NFACES call makepoly() call color(colface(i)) x = pnts(1, faces(1, i)) y = pnts(2, faces(1, i)) z = pnts(3, faces(1, i)) call move(x, y, z) do j = 2, NSIDES x = pnts(1, faces(j,i)) y = pnts(2, faces(j,i)) z = pnts(3, faces(j,i)) call draw(x, y, z) enddo call closepoly() enddo
call closeobj()
end subroutine maketheobject
end program demo_lookat
| lookat (3) | March 11, 2021 |
