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FDISTRT.FOR
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2000-02-11
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c
c Demonstrate how to use non-square viewports, the associated
c distortion caused and how to fix it.
c
program fdistrt
integer BLACK, RED, GREEN, YELLOW, BLUE, MAGENTA, CYAN, WHITE
parameter(BLACK = 0)
parameter(RED = 1)
parameter(GREEN = 2)
parameter(YELLOW = 3)
parameter(BLUE = 4)
parameter(MAGENTA = 5)
parameter(CYAN = 6)
parameter(WHITE = 7)
character device*50, buf*120
real xfact, yfact
print*,'Enter output device:'
read(*,'(a)') device
call vinit(device)
call color(BLACK)
call clear
c
c Make the viewport the same size as the screen/window.
c
call getfactors(xfact, yfact)
call viewport(-1.0, xfact, -1.0, yfact)
c
c Draw a square. (Looks like a rectangle, if the viewport
c wasn't "accidentally" square)
c
call color(1)
call rect(-0.5, -0.5, 0.5, 0.5)
c
c Tell them what it is.
c
call move2(-1.0, 0.9)
write(buf,'(''Distorted square (viewport(-1, '',
+ F7.3, '', -1, '', F7.3, ''))'')') xfact, yfact
call drawstr(buf)
call getkey
c
c Fix up the distortion (The actual formula to fix
c the distortion is (viewport.xmax * (1 + xfact) / 2.0),
c and similar for the y axis.
c
call ortho2(-1.0, xfact, -1.0, yfact)
c
c Draw another square (Really is square this time)
c
call color(3)
call rect(-0.5, -0.5, 0.5, 0.5)
c
c Tell them what it is.
c
call move2(-1.0, -0.9)
write(buf,'(''Fixed up square with ortho2(-1, '',
+ F7.3, '', -1, '', F7.3, '')'')') xfact, yfact
call drawstr(buf)
call getkey
c
c Do it with world coords going from 0 - 5, 0 - 5.
c Reset square viewport.
c
call color(0)
call clear
call viewport(-1.0, 1.0, -1.0, 1.0)
call ortho2(0.0, 5.0, 0.0, 5.0)
call textsize(0.1, 0.1)
c
c Square from 1 to 3. (Really is square)
c
call color(2)
call rect(1.0, 1.0, 3.0, 3.0)
call move2(0.0, 4.5)
call drawstr('Square from 0 - 3, 0 - 3')
call getkey
c
c Distort it with a non-square viewport.
c
call viewport(-1.0, xfact, -1.0, yfact)
call color(4)
call rect(1.0, 1.0, 3.0, 3.0)
call move2(0.0, 0.5)
call drawstr('Distorted square from 0 - 3, 0 - 3')
call getkey
c
c Fix the distortion.
c
call ortho2(0.0, 5.0 * (1.0 + xfact) / 2.0, 0.0,
+ 5.0 * (1.0 + yfact) / 2.0)
call color(5)
call rect(1.0, 1.0, 3.0, 3.0)
call move2(0.0, 2.5)
call drawstr('Fixed up square from 0 - 3, 0 - 3')
call getkey
call vexit
end