Xiaolin Wu's line algorithm: Difference between revisions

Revision as of 19:55, 29 January 2014

Revision as of 16:51, 21 November 2014

Line 10:

<syntaxhighlight lang="pascal">

function plot(x, y, c) is

plot the pixel at (x, y) with brightness c (where 0 ≤ c ≤ 1)

// integer part of x

function ipart(x) is

return 'integer part of int(x')

function round(x) is

return ipart(x + 0.5)

// fractional part of x

function fpart(x) is

if x < 0

return 'fractional part of x'

return 1 - (x - floor(x))

return x - floor(x)

function rfpart(x) is

return 1 - fpart(x)

function drawLine(x0,y0,x1,y1) is

boolean steep := abs(y1 - y0) > abs(x1 - x0)

if steep then

swap(x0, y0)

swap(x1, y1)

end if

if x0 > x1 then

swap(x0, x1)

swap(y0, y1)

end if

dx := x1 - x0

dy := y1 - y0

gradient := dy / dx

// handle first endpoint

xend := round(x0)

yend := y0 + gradient * (xend - x0)

xgap := rfpart(x0 + 0.5)

xpxl1 := xend //this will be used in the main loop

ypxl1 := ipart(yend)

if steep then

plot(ypxl1, xpxl1, rfpart(yend) * xgap)

plot(ypxl1+1, xpxl1, fpart(yend) * xgap)

else

plot(xpxl1, ypxl1 , rfpart(yend) * xgap)

plot(xpxl1, ypxl1+1, fpart(yend) * xgap)

end if

intery := yend + gradient // first y-intersection for the main loop

// handle second endpoint

xend := round(x1)

yend := y1 + gradient * (xend - x1)

xgap := fpart(x1 + 0.5)

xpxl2 := xend //this will be used in the main loop

ypxl2 := ipart(yend)

if steep then

plot(ypxl2 , xpxl2, rfpart(yend) * xgap)

plot(ypxl2+1, xpxl2, fpart(yend) * xgap)

else

plot(xpxl2, ypxl2, rfpart(yend) * xgap)

plot(xpxl2, ypxl2+1, fpart(yend) * xgap)

end if

// main loop

function drawLine(x0,y0,x1,y1) is

for x from xpxl1 + 1 to xpxl2 - 1 do

boolean steep := abs(y1 - y0) if> abs(x1 steep- thenx0)

plot(ipart(intery) , x, rfpart(intery))

if steep then

plot(ipart(intery)+1, x, fpart(intery))

swap(x0, elsey0)

swap(x1, y1)

end if

if x0 > x1 then

swap(x0, x1)

swap(y0, y1)

end if

dx := x1 - x0

dy := y1 - y0

gradient := dy / dx

// handle first endpoint

xend := round(x0)

yend := y0 + gradient * (xend - x0)

xgap := rfpart(x0 + 0.5)

xpxl1 := xend // this will be used in the main loop

ypxl1 := ipart(yend)

if steep then

plot(ypxl1, xpxl1, rfpart(yend) * xgap)

plot(ypxl1+1, xpxl1, fpart(yend) * xgap)

else

plot(xpxl1, ypxl1 , rfpart(yend) * xgap)

plot(xpxl1, ypxl1+1, fpart(yend) * xgap)

end if

intery := yend + gradient // first y-intersection for the main loop

// handle second endpoint

xend := round(x1)

yend := y1 + gradient * (xend - x1)

xgap := fpart(x1 + 0.5)

xpxl2 := xend //this will be used in the main loop

ypxl2 := ipart(yend)

if steep then

plot(ypxl2 , xpxl2, rfpart(yend) * xgap)

plot(ypxl2+1, xpxl2, fpart(yend) * xgap)

else

plot(xpxl2, ypxl2, rfpart(yend) * xgap)

plot(xpxl2, ypxl2+1, fpart(yend) * xgap)

end if

// main loop

for x from xpxl1 + 1 to xpxl2 - 1 do

if steep then

plot(ipart(intery) , x, rfpart(intery))

plot(ipart(intery)+1, x, fpart(intery))

else

plot(x, ipart (intery), rfpart(intery))

plot(x, ipart (intery)+1, fpart(intery))

end if

intery := intery + gradient

end function

</syntaxhighlight>