Sample program:
program demo_perspective
!
! Shows various combinations of viewing and projection transformations
use M_draw
!
character(len=50) :: device
integer :: ios
!
print*,’Enter output device:’
read(*,’(a)’,iostat=ios)device
if(ios.ne.0)device=’ ’
!
call vinit(device)
!
call color(D_BLACK)
call clear()
!
! we want to draw just within the boundaries of the screen
!
call viewport(-0.9, 0.9, -0.9, 0.9)
!
! set the world size
!
call ortho2(-5.0, 5.0, -5.0, 5.0)
!
! draw a boundary frame
!
call color(D_RED)
call rect(-5.0, -5.0, 5.0, 5.0)
!
! 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, 0.1, 1000.0)
!
! we want the drawing to be done with our eye point at (5.0, 8.0, 5.0)
! looking towards (0.0, 0.0, 0.0). The last parameter gives a twist
! in degrees around the line of sight, in this case zero.
!
call lookat(5.0, 8.0, 5.0, 0.0, 0.0, 0.0, 0.0)
!
call drawtetra()
!
! set the text size
!
call textsize(0.6, 0.9)
!
call move2(-4.5, -4.5)
call drawstr(’perspective/lookat’)
!
idum=getkey()
!
! window can also be used to give a perspective projection. Its
! arguments are 6 clipping planes, left, right, bottom, top, near,
! and far.
!
call window(-5.0, 5.0, -5.0, 5.0, -5.0, 5.0)
!
! as window replaces the current transformation matrix we must
! specify our viewpoint again.
!
call lookat(5.0, 8.0, 5.0, 0.0, 0.0, 0.0, 0.0)
!
call color(D_BLACK)
call clear()
!
call color(D_GREEN)
call rect(-5.0, -5.0, 5.0, 5.0)
!
call drawtetra()
!
call textsize(0.6, 0.9)
call move2(-4.5,-4.5)
call drawstr(’window/lookat’)
!
idum=getkey()
!
! set up our original perspective projection again.
!
call perspective(40.0, 1.0, 0.1, 1000.0)
!
! polarview also specifies our viewpoint, but, unlike lookat, in polar
! coordinates. Its arguments are the distance from the world origin, an
! azimuthal angle in the x-y plane measured from the y axis, an
! incidence angle in the y-z plane measured from the z axis, and a
! twist around the line of sight.
!
call polarview(15.0, 30.0, 30.0, 30.0)
!
call color(D_BLACK)
call clear()
!
call color(D_MAGENTA)
call rect(-5.0, -5.0, 5.0, 5.0)
!
call drawtetra()
!
call move2(-4.5,-4.5)
call textsize(0.6, 0.9)
call drawstr(’perspective/polarview’)
!
idum=getkey()
!
! once more with window for comparison
!
call window(-4.0, 4.0, -4.0, 4.0, -4.0, 4.0)
call polarview(6.0, 20.0, -30.0, 70.0)
!
call color(D_BLACK)
call clear()
!
call color(D_YELLOW)
call rect(-5.0, -5.0, 5.0, 5.0)
!
call drawtetra()
!
call move2(-4.5,-4.5)
call textsize(0.6, 0.9)
call drawstr(’window/polarview’)
!
idum=getkey()
!
call vexit()
!
contains
!
subroutine drawtetra()
!
! generate a tetrahedron as a series of move draws
!
call move(-0.5, 0.866, -0.5)
call draw(-0.5, -0.866, -0.5)
call draw( 1.0, 0.0, -0.5)
call draw(-0.5, 0.866, -0.5)
call draw( 0.0, 0.0, 1.5)
call draw(-0.5, -0.866, -0.5)
call move( 1.0, 0.0, -0.5)
call draw( 0.0, 0.0, 1.5)
!
! Label the vertices.
!
call color(D_WHITE)
call textsize(0.3, 0.5)
call move(-0.5, 0.866, -0.5)
call drawchar(’a’)
call move(-0.5, -0.866, -0.5)
call drawchar(’b’)
call move( 1.0, 0.0, -0.5)
call drawchar(’c’)
call move( 0.0, 0.0, 1.5)
call drawchar(’d’)
!
end subroutine drawtetra
!
end program demo_perspective
