Xiaolin Wu's line algorithm: Difference between revisions
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label .wu.l -image $img
pack .wu.l</lang>
=={{header|Yabasic}}==
{{trans|Phix}}
<lang Yabasic>bresline = false // space toggles, for comparison
rB = 255 : gB = 255 : bB = 224
rL = 0 : gL = 0 : bL = 255
sub round(x)
return int(x + .5)
end sub
sub plot(x, y, c, steep)
// plot the pixel at (x, y) with brightness c (where 0 <= c <= 1)
local t, C
if steep then t = x : x = y : y = t end if
C = 1 - c
color rL * c + rB * C, gL * c + gB * C, bL * c + bB * C
dot x, y
end sub
sub plot2(x, y, f, xgap, steep)
plot(x, y, (1 - f) * xgap, steep)
plot(x, y + 1, f * xgap, steep)
end sub
sub draw_line(x0, y0, x1, y1)
local steep, t, dx, dy, gradient, xend, yend, xgap, xpxl1, ypxl1, xpxl2, ypxl2, intery
if bresline then
line x0, y0, x1, y1
return
end if
steep = abs(y1 - y0) > abs(x1 - x0)
if steep then
t = x0 : x0 = y0 : y0 = t
t = x1 : x1 = y1 : y1 = t
end if
if x0 > x1 then
t = x0 : x0 = x1 : x1 = t
t = y0 : y0 = y1 : y1 = t
end if
dx = x1 - x0
dy = y1 - y0
if dx = 0 then
gradient = 1
else
gradient = dy / dx
end if
// handle first endpoint
xend = round(x0)
yend = y0 + gradient * (xend - x0)
xgap = 1 - frac(x0 + 0.5)
xpxl1 = xend // this will be used in the main loop
ypxl1 = int(yend)
plot2(xpxl1, ypxl1, frac(yend), xgap, steep)
intery = yend + gradient // first y-intersection for the main loop
// handle second endpoint
xend = round(x1)
yend = y1 + gradient * (xend - x1)
xgap = frac(x1 + 0.5)
xpxl2 = xend // this will be used in the main loop
ypxl2 = int(yend)
plot2(xpxl2, ypxl2, frac(yend), xgap, steep)
// main loop
for x = xpxl1 + 1 to xpxl2 - 1
plot2(x, int(intery), frac(intery), 1, steep)
intery = intery + gradient
next x
end sub
w = 640 : h = 480
open window w, h
color 0, 0, 255
draw_line(0, 0, 200, 200)
draw_line(w, 0, 200, 200)
draw_line(0, h, 200, 200)
draw_line(w, h, 200, 200)</lang>
[[Category:Geometry]]
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