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-- Allow user to draw one or more straight lines by clicking end points.
-- Author: Andrew Trevorrow (andrew@trevorrow.com), Apr 2016.
local g = golly()
local gp = require "gplus"
local oldline = {}
local firstcell = {} -- pos and state of the 1st cell clicked
local drawstate = g.getoption("drawingstate")
--------------------------------------------------------------------------------
local function drawline(x1, y1, x2, y2)
-- draw a line of cells from x1,y1 to x2,y2 using Bresenham's algorithm;
-- we also return the old cells in the line so we can erase line later
local oldcells = {}
-- note that x1,y1 has already been drawn
if x1 == x2 and y1 == y2 then
g.update()
return oldcells
end
local dx = x2 - x1
local ax = math.abs(dx) * 2
local sx = 1
if dx < 0 then sx = -1 end
local dy = y2 - y1
local ay = math.abs(dy) * 2
local sy = 1
if dy < 0 then sy = -1 end
if ax > ay then
local d = ay - (ax / 2)
while x1 ~= x2 do
oldcells[#oldcells+1] = {x1, y1, g.getcell(x1, y1)}
g.setcell(x1, y1, drawstate)
if d >= 0 then
y1 = y1 + sy
d = d - ax
end
x1 = x1 + sx
d = d + ay
end
else
local d = ax - (ay / 2)
while y1 ~= y2 do
oldcells[#oldcells+1] = {x1, y1, g.getcell(x1, y1)}
g.setcell(x1, y1, drawstate)
if d >= 0 then
x1 = x1 + sx
d = d - ay
end
y1 = y1 + sy
d = d + ax
end
end
oldcells[#oldcells+1] = {x2, y2, g.getcell(x2, y2)}
g.setcell(x2, y2, drawstate)
g.update()
return oldcells
end
--------------------------------------------------------------------------------
local function eraseline(oldcells)
for _, t in ipairs(oldcells) do
g.setcell( table.unpack(t) )
end
end
--------------------------------------------------------------------------------
function drawlines()
local started = false
local oldmouse = ""
local startx, starty, endx, endy
while true do
local event = g.getevent()
if event:find("click") == 1 then
-- event is a string like "click 10 20 left altctrlshift"
local evt, x, y, butt, mods = gp.split(event)
oldmouse = x .. ' ' .. y
if started then
-- draw permanent line from start pos to end pos
endx = tonumber(x)
endy = tonumber(y)
drawline(startx, starty, endx, endy)
-- this is also the start of another line
startx = endx
starty = endy
oldline = {}
firstcell = {}
else
-- start first line
startx = tonumber(x)
starty = tonumber(y)
firstcell = { startx, starty, g.getcell(startx, starty) }
g.setcell(startx, starty, drawstate)
g.update()
started = true
g.show("Click where to end this line (and start another line)...")
end
else
-- event might be "" or "key m none"
if #event > 0 then g.doevent(event) end
local mousepos = g.getxy()
if started and #mousepos == 0 then
-- erase old line if mouse is not over grid
if #oldline > 0 then
eraseline(oldline)
oldline = {}
g.update()
end
elseif started and #mousepos > 0 and mousepos ~= oldmouse then
-- mouse has moved, so erase old line (if any) and draw new line
if #oldline > 0 then eraseline(oldline) end
local x, y = gp.split(mousepos)
oldline = drawline(startx, starty, tonumber(x), tonumber(y))
oldmouse = mousepos
end
end
end
end
--------------------------------------------------------------------------------
g.show("Click where to start line...")
local oldcursor = g.getcursor()
g.setcursor("Draw")
local status, err = xpcall(drawlines, gp.trace)
if err then g.continue(err) end
-- the following code is executed even if error occurred or user aborted script
g.setcursor(oldcursor)
if #oldline > 0 then eraseline(oldline) end
if #firstcell > 0 then
local x, y, s = table.unpack(firstcell)
g.setcell(x, y, s)
end
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