Implement 2D bresenham line drawing for #35

We need it to be 3D though.
We essentially just ported f51f153459/src/index.js to Lua, as https://medium.com/geekculture/bresenhams-line-drawing-algorithm-2e0e953901b3 was WRONG as it didn't handle all edge cases and this one is much more optimised.
This commit is contained in:
Starbeamrainbowlabs 2022-09-17 23:27:57 +01:00
parent 382194321b
commit 763ae3db8d
Signed by: sbrl
GPG Key ID: 1BE5172E637709C2
1 changed files with 157 additions and 0 deletions

157
bresenham.lua Normal file
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local Vector3 = dofile("worldeditadditions/utils/vector3.lua")
local function make_grid(size)
local grid = {}
for y=1,size.y do
for x=1,size.x do
grid[(size.x * y) + x] = 0
end
end
return {
size = size,
data = grid
}
end
local function index(grid, pos)
return (grid.size.x * pos.y) + pos.x
end
local function grid_to_string(grid)
local result = {}
for y=1,grid.size.y do
for x=1,grid.size.x do
local i = index(grid, Vector3.new(x, y))
if grid.data[i] == 0 then
table.insert(result, "#")
elseif grid.data[i] == 1 then
table.insert(result, " ")
elseif grid.data[i] < 10 then
table.insert(result, tostring(grid.data[i]))
else
table.insert(result, "?")
end
end
table.insert(result, "\n")
end
return table.concat(result, "")
end
--- Draws a line using Bresenham's algorithm in 2d.
-- Implemented ported from https://github.com/anushaihalapathirana/Bresenham-line-drawing-algorithm/blob/f51f153459a1656bfb1f433edc75e6644a052bb2/src/index.js
-- @param grid Grid The grid to draw on.
-- @param pos1 Vector3 The starting point of the line.
-- @param pos2 Vector3 The ending point of the line.
-- @param value number The number to fill in grid cells we draw in.
-- @returns void
local function draw_line_2d(grid, pos1, pos2, value)
if not value then value = 1 end
if pos1 == pos2 then
grid.data[index(grid, pos1)] = value
return
end
grid.data[index(grid, pos1)] = value -- plot pos1
local delta = pos2 - pos1
local absdelta = delta:abs()
local delta_error = (2 * absdelta.y) - absdelta.x -- d
if absdelta.x <= absdelta.y then delta_error = (2 * absdelta.x) - absdelta.y end
local pos_current = pos1:clone()
local steps = 0
local limit = absdelta.y
if absdelta.x > absdelta.y then limit = absdelta.x end
for _=1,limit do
local do_x = false
local do_y = false
if absdelta.x > absdelta.y then
do_x = true
if delta_error < 0 then
delta_error = delta_error + 2*absdelta.y
else
do_y = true
delta_error = delta_error + (2*absdelta.y - 2*absdelta.x)
end
else
do_y = true
if delta_error < 0 then
delta_error = delta_error + 2*absdelta.x
else
do_x = true
delta_error = delta_error + (2*absdelta.x) - (2*absdelta.y)
end
end
if do_x then
local acc = 1
if delta.x < 0 then acc = -1 end
pos_current.x = pos_current.x + acc
end
if do_y then
local acc = 1
if delta.y < 0 then acc = -1 end
pos_current.y = pos_current.y + acc
end
local i = index(grid, pos_current)
grid.data[i] = value
steps = steps + 1
end
end
local size = Vector3.new(120, 40)
local grid = make_grid(size)
-- draw_line_2d(grid, Vector3.new(10, 10), Vector3.new(40, 10))
-- draw_line_2d(grid, Vector3.new(70, 10), Vector3.new(70, 10))
draw_line_2d(grid, Vector3.new(75, 10), Vector3.new(75, 40))
draw_line_2d(grid, Vector3.new(80, 40), Vector3.new(80, 10))
-- local centre = Vector3.new(25, 25)
-- draw_line_2d(grid, centre, Vector3.new(0, 0))
-- draw_line_2d(grid, centre, Vector3.new(5, 0))
-- draw_line_2d(grid, centre, Vector3.new(10, 0))
-- draw_line_2d(grid, centre, Vector3.new(15, 0))
-- draw_line_2d(grid, centre, Vector3.new(20, 0))
-- draw_line_2d(grid, centre, Vector3.new(25, 0))
-- draw_line_2d(grid, centre, Vector3.new(30, 0), 3)
for i=1,9 do
print("LINE", i)
local pos1 = Vector3.new(
math.random(0, size.x),
math.random(0, size.y)
)
local pos2 = Vector3.new(
math.random(0, size.x),
math.random(0, size.y)
)
draw_line_2d(grid, pos1, pos2)
end
-- draw_line_2d(grid,
-- Vector3.new(3, 4),
-- Vector3.new(8, 9)
-- )
-- draw_line_2d(grid,
-- Vector3.new(10, 9),
-- Vector3.new(15, 4)
-- )
-- draw_line_2d(grid,
-- Vector3.new(20, 10),
-- Vector3.new(40, 20)
-- )
-- draw_line_2d(grid,
-- Vector3.new(10, 9),
-- Vector3.new(55, 4)
-- )
print(grid_to_string(grid))