clipper

MoKaLux · September 2019

I tried to understand the clipper plugin and this is what I have got:

require "clipper"
local subject = Polygon.new()
subject:addPoint(0, 0)
subject:addPoint(16, 16)
subject:addPoint(16, 32)
subject:addPoint(0, 32)
subject:addPoint(-16, 16)
subject:addPoint(0, 0)
 
local clipper = Polygon.new()
clipper:addPoint(0, 0)
clipper:addPoint(32, 32)
clipper:addPoint(32, 64)
clipper:addPoint(0, 64)
clipper:addPoint(-32, 32)
clipper:addPoint(0, 0)
 
local myclipper = Clipper.new()
myclipper:addSubjectPolygon(subject, Polygon.FILL_EVEN_ODD, true)
myclipper:addClipPolygon(clipper, Polygon.FILL_EVEN_ODD, true)
local myc = myclipper:getDifference(subject, clipper)
local myi = myclipper:getIntersection(subject, clipper)
local x, y, w, h = myclipper:getBounds(subject, clipper)
print(x) -- ok
 
--local solution = Polygon.new() -- ???
--stage:addChild(myclipper) -- not ok

And I am stuck, I don't know how to retrieve the getDifference value and draw the solution polygon.

keszegh · September 2019

i've found a different lua binding:
https://luapower.com/clipper
it seems it has a different api from the current gideros clipper.
perhaps this could replace the current one in gideros?

keszegh · September 2019

for the current one this could help: https://github.com/gideros/giderosplugins/blob/master/Clipper/apireference.html

i did not test it, but according to the docs i think something like this would be better:
myclipper:addSubjectPolygon(subject)
myclipper:addClipPolygon(clipper)
local myc = myclipper:getDifference(Polygon.FILL_EVEN_ODD, Polygon.FILL_EVEN_ODD)

and then myc is still just an abstract polygon object, not a sprite, so first from reading its vertices (by using myc:getPoints() ) you need to build a sprite using path2d for example. and then that can be added to the stage.

MoKaLux · September 2019

@keszegh yes that looks very similar to what we have in gideros. I don't think I am going to need it soon but I was just curious about how to use it a simple example would be nice for the wiki.

Thank you for your insights I am going to try what you suggested.

MoKaLux · September 2019

keszegh said:
for the current one this could help: https://github.com/gideros/giderosplugins/blob/master/Clipper/apireference.html
and then myc is still just an abstract polygon object, not a sprite, so first from reading its vertices (by using myc:getPoints() ) you need to build a sprite using path2d for example. and then that can be added to the stage.

(by using myc:getPoints() ) This function does not exist. I think the points are hold in the table:
local myc = myclipper:getDifference(Polygon.FILL_EVEN_ODD, Polygon.FILL_EVEN_ODD)

But I cannot retrieve anything from this table!

keszegh · September 2019

well, that's a problem, according to the reference, it should.
in zerobrane studio you can watch tables with all the subvalues and then it's easier to see what and how is stored in the myc object.

MoKaLux · September 2019

yes I have tried with this function (I don't use zerobrane).

function tprint (tbl, indent)
  if not indent then indent = 0 end
  local toprint = string.rep(" ", indent) .. "{\r\n"
  indent = indent + 2 
  for k, v in pairs(tbl) do
    toprint = toprint .. string.rep(" ", indent)
    if (type(k) == "number") then
      toprint = toprint .. "[" .. k .. "] = "
    elseif (type(k) == "string") then
      toprint = toprint  .. k ..  "= "   
    end
    if (type(v) == "number") then
      toprint = toprint .. v .. ",\r\n"
    elseif (type(v) == "string") then
      toprint = toprint .. "\"" .. v .. "\",\r\n"
    elseif (type(v) == "table") then
      toprint = toprint .. tprint(v, indent + 2) .. ",\r\n"
    else
      toprint = toprint .. "\"" .. tostring(v) .. "\",\r\n"
    end
  end
  toprint = toprint .. string.rep(" ", indent-2) .. "}"
  return toprint
end

But the result is something like that:

print(tprint(myi))

{
  [1] =     {
      __userdata= "userdata: 015DAB18",
    },
}

And that's chinese for me.

MoKaLux · September 2019

no worries though.

My last attempt:

require "clipper"
local subject = Polygon.new(Polygon.FILL_EVEN_ODD)
subject:addPoint(0, 0)
subject:addPoint(16, 16)
subject:addPoint(16, 32)
subject:addPoint(0, 32)
subject:addPoint(-16, 16)
subject:addPoint(-32, 96)
subject:addPoint(0, 0)
 
local clipper = Polygon.new(Polygon.FILL_EVEN_ODD)
clipper:addPoint(0, 0)
clipper:addPoint(32, 32)
clipper:addPoint(32, 64)
clipper:addPoint(0, 64)
clipper:addPoint(-32, 32)
clipper:addPoint(-48, 64)
clipper:addPoint(0, 0)
 
local psubject = subject:getPoints()
local pclipper = clipper:getPoints()
local mypixel
for k, v in ipairs(psubject) do
	mypixel = Pixel.new(0xff0000, 0.25, 8, 8)
	mypixel:setPosition(v[1] + 128, v[2] + 128)
	stage:addChild(mypixel)
end
for k, v in ipairs(pclipper) do
	mypixel = Pixel.new(0x000000, 0.25, 8, 8)
	mypixel:setPosition(v[1] + 128, v[2] + 128)
	stage:addChild(mypixel)
end
 
local myclipper = Clipper.new()
myclipper:addSubjectPolygon(subject)
myclipper:addClipPolygon(clipper)
myclipper:getDifference(Polygon.FILL_EVEN_ODD, Polygon.FILL_EVEN_ODD)
local x, y, w, h = myclipper:getBounds(subject, clipper)
mypixel = Pixel.new(0x0000ff, 0.1, w, h)
mypixel:setPosition(x + 128, y + 128)
stage:addChild(mypixel)
 
local solution = Polygon.new()
 
--stage:addChild(myclipper) -- not ok

I feel I am almost there but the final solution polygon is missing!

MoKaLux · September 2019

I found this example:

Polygon clipping example

local clipper = require 'clipper'
 
local p1 = clipper.Path()
p1:add(100,100)
p1:add(150,100)
p1:add(150,150)
p1:add(100,150)
 
local p2 = clipper.Path()
p2:add(100,120)
p2:add(150,120)
p2:add(150,130)
p2:add(100,130)
 
local cl = clipper.Clipper()
cl:addPath(p1,'subject')
cl:addPath(p2,'clip')
local out = cl:execute('difference')

But I don't see the execute in the gideros clipper implementation! Almost there?!

hgy29 · September 2019

@MoKaLux, reading the c++ code it looks like the result of getDifference/getIntersection and others is a list of Polygon objects, so you should iterate over your ‘myc’ and call getPoints() for each entry.

keszegh · September 2019

so following @hgy29 's remark the following code gives me (in zbs) the following result:

require "clipper"
local subject = Polygon.new()
subject:addPoint(0, 0)
subject:addPoint(16, 16)
subject:addPoint(16, 32)
subject:addPoint(0, 32)
subject:addPoint(-16, 16)
--subject:addPoint(0, 0)
 
local clipper = Polygon.new()
clipper:addPoint(0, 0)
clipper:addPoint(32, 32)
clipper:addPoint(32, 64)
clipper:addPoint(0, 64)
clipper:addPoint(-32, 32)
--clipper:addPoint(0, 0)
 
local myclipper = Clipper.new()
myclipper:addSubjectPolygon(subject)
myclipper:addClipPolygon(clipper)
local myc = myclipper:getUnion(Polygon.FILL_EVEN_ODD, Polygon.FILL_EVEN_ODD)
--iterate over all polygons in the union:
for key,value in pairs(myc) do 	 
    print(key)
    print(value:getPoints())
end

result:
1
{{0, 0}, {32, 32}, {32, 64}, {0, 64}, {-32, 32}}
that is, indeed myc consists of tables storing polygons, which can be read using getPoints.

note that i used getUnion in my example to make sure that the result is not empty!

keszegh · September 2019

also i think in your example the last "subject:addPoint(0, 0)" for each polygon is probably not necessary as it anyway closes the polygon.
and if you want difference then better exchange clipper and subject as otherwise you get an empty difference (as the bigger contains the smaller one). that's why i used union in my example to avoid this.

keszegh · September 2019

e.g. when you exchange clipper and subject and generate difference:

myclipper:addSubjectPolygon(clipper)
myclipper:addClipPolygon(subject)
local myc = myclipper:getDifference(Polygon.FILL_EVEN_ODD, Polygon.FILL_EVEN_ODD)

you correctly get:
1
{{0, 32}, {16, 32}, {16, 16}, {32, 32}, {32, 64}, {0, 64}, {-32, 32}, {-16, 16}}

MoKaLux · September 2019

thank you guys, I am going to follow your example, make some nice code and add it to the wiki. I was so curious about this clipper thing. You are the best! Viva gideros.

MoKaLux · September 2019

ok I had it working but what a mess!

require "clipper"
function createPolygon(xpoints, xcolor)
	local myshape = Shape.new()
	myshape:setFillStyle(Shape.SOLID, xcolor or 0xff0000, 1)
	myshape:beginPath()
	myshape:moveTo(xpoints:getPoints()[1][1], xpoints:getPoints()[1][2])
	--print(#xpoints:getPoints())
	for p = 2, #xpoints:getPoints() do
		myshape:lineTo(xpoints:getPoints()[p][1], xpoints:getPoints()[p][2])
	end
	myshape:endPath()
	myshape:setPosition(128, 128)
	stage:addChild(myshape)
end
 
local subject = Polygon.new()
subject:addPoint(-32, -32)
subject:addPoint(32, -32)
subject:addPoint(32, 32)
subject:addPoint(-32, 32)
 
local clip = Polygon.new()
clip:addPoint(-16, -16)
clip:addPoint(0, 0)
clip:addPoint(16, -16)
clip:addPoint(16, 16)
clip:addPoint(-16, 16)
 
--print(clip:getPoints()[3][2])
createPolygon(subject)
createPolygon(clip, 0x00ff00)
 
function createShape(xtable)
	local myshape = Shape.new()
	myshape:setFillStyle(Shape.SOLID, 0x0000ff, 1)
	myshape:beginPath()
	myshape:moveTo(xtable.x[1], xtable.y[1])
	for c = 2, #xtable.x do
		myshape:lineTo(xtable.x[c], xtable.y[c])
	end
	myshape:endPath()
	myshape:setPosition(128, 128)
	stage:addChild(myshape)
end
 
local myclipper = Clipper.new()
local mysolution = {}
mysolution.x = {}
mysolution.y = {}
 
myclipper:addSubjectPolygon(subject)
myclipper:addClipPolygon(clip)
--local myc = myclipper:getUnion(Polygon.FILL_EVEN_ODD, Polygon.FILL_EVEN_ODD)
--local myc = myclipper:getDifference(Polygon.FILL_EVEN_ODD, Polygon.FILL_EVEN_ODD)
--local myc = myclipper:getIntersection(Polygon.FILL_EVEN_ODD, Polygon.FILL_EVEN_ODD)
--local myc = myclipper:getIntersection(Polygon.FILL_NON_ZERO, Polygon.FILL_NON_ZERO)
local myc = myclipper:getIntersection(Polygon.FILL_POSITIVE, Polygon.FILL_POSITIVE)
--local myc = myclipper:getIntersection(Polygon.FILL_NEGATIVE, Polygon.FILL_NEGATIVE)
--local myc = myclipper:getIntersection(Polygon.FILL_POSITIVE, Polygon.FILL_NEGATIVE)
--local myc = myclipper:getExclusion(Polygon.FILL_EVEN_ODD, Polygon.FILL_EVEN_ODD)
for k, v in ipairs(myc) do
	for k1, v1 in ipairs(v:getPoints()) do
		for i = 1, #v1 do
			if i % 2 == 1 then -- x position
				mysolution.x[#mysolution.x + 1] = v1[i]
			else -- y position
				mysolution.y[#mysolution.y + 1] = v1[i]
			end
		end
	end
	createShape(mysolution)
end

You can copy paste the code and it should work (you need to add the clipper plugin).
You can uncomment the local myc lines to see different effects.

But what a mess. I saw somewhere in this forum a clipping example that was quite good. I don't see the point of this clipper plugin and I won't add it to the wiki. I suggest to remove it completely from gideros! We could gain back a few kb

Next 3D in gideros

MoKaLux · September 2019

some clipper image: the blue part is the clipper result. It does not work well with every type of clipping though.

keszegh · September 2019

there are clipping situations for which you need this plugin. e.g. to compute the exact shadows of multiple light sources with obstacles, which was my original motivation when i asked @ar2rsawseen to add this plugin. at the end i did not pursue this project at the time.

MoKaLux · September 2019

oh so you are the one

Will anybody ever use it? that is the question. I still think we should remove it completely from gideros because people will want to know how this work and try to use it.

Apollo14 · September 2019

let it be

keszegh · September 2019

@MoKaLux , this is useful stuff just it maybe should have a name different from clipping to avoid confusement, in 3d software they call it boolean operations.

oleg · September 2019

keszegh said:
@MoKaLux , this is useful stuff just it maybe should have a name different from clipping to avoid confusement, in 3d software they call it boolean operations.

In the illustrator this is also called boolean operations ..

Howdy, Stranger!

Categories

In this Discussion

Top Posters

clipper

Comments

Howdy, Stranger!

Quick Links

Categories

In this Discussion

Top Posters

clipper

Comments