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fix c64 bresenham line inaccuracy

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This commit is contained in:
Irmen de Jong 2021-03-09 20:44:06 +01:00
parent 62ec77e148
commit 6bd205c02a
2 changed files with 30 additions and 38 deletions
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21
compiler/res/prog8lib/c64/graphics.p8
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@ -34,7 +34,6 @@ graphics {
sub line(uword @zp x1, ubyte @zp y1, uword @zp x2, ubyte @zp y2) {
; Bresenham algorithm.
; This code special-cases various quadrant loops to allow simple ++ and -- operations.
; TODO there are some slight errors at the first/last pixels in certain slopes...??
if y1>y2 {
; make sure dy is always positive to have only 4 instead of 8 special cases
swap(x1, x2)
@ -62,8 +61,8 @@ graphics {
dx = -dx
positive_ix = false
}
dx *= 2
dy *= 2
word @zp dx2 = dx*2
word @zp dy2 = dy*2
internal_plotx = x1
if dx >= dy {
@ -73,10 +72,10 @@ graphics {
if internal_plotx==x2
return
internal_plotx++
d += dy
d += dy2
if d > dx {
y1++
d -= dx
d -= dx2
}
}
} else {
@ -85,10 +84,10 @@ graphics {
if internal_plotx==x2
return
internal_plotx--
d += dy
d += dy2
if d > dx {
y1++
d -= dx
d -= dx2
}
}
}
@ -100,10 +99,10 @@ graphics {
if y1 == y2
return
y1++
d += dx
d += dx2
if d > dy {
internal_plotx++
d -= dy
d -= dy2
}
}
} else {
@ -112,10 +111,10 @@ graphics {
if y1 == y2
return
y1++
d += dx
d += dx2
if d > dy {
internal_plotx--
d -= dy
d -= dy2
}
}
}

47
examples/test.p8
View File

@ -1,39 +1,32 @@
%import textio
%import graphics
%import floats
%import test_stack
%zeropage dontuse
main {
sub start() {
graphics.enable_bitmap_mode()
uword xx
float fl
float fltotal=0.0
ubyte ub = 22
ubyte yy
ub = 22
fl = ub as float
floats.print_f(fl)
txt.nl()
ub = 255
fl = ub as float
floats.print_f(fl)
txt.nl()
xx = 123
fl = xx as float
floats.print_f(fl)
txt.nl()
xx = 55555
fl = xx as float
floats.print_f(fl)
txt.nl()
graphics.line(150,50,150,50)
fltotal=0.0
for xx in 1 to 255 {
fl = xx as float
fltotal = fl * fl
for yy in 0 to 199-60 step 16 {
for xx in 0 to 319-50 step 16 {
graphics.line(30+xx, 10+yy, 50+xx, 30+yy)
graphics.line(49+xx, 30+yy, 10+xx, 30+yy)
graphics.line(11+xx, 29+yy, 29+xx, 11+yy)
; triangle 2, counter-clockwise
graphics.line(30+xx, 40+yy, 10+xx, 60+yy)
graphics.line(11+xx, 60+yy, 50+xx, 60+yy)
graphics.line(49+xx, 59+yy, 31+xx,41+yy)
}
}
test_stack.test()
repeat {
}
}
}