Sharing code for a filled polygon

General
1

Hello,

I needed some code for a filled polygon (my actual problem was a triangle)
So I made it and thought I would share.
Use the code in setup() and the returned image in draw(), because the generation is kind of slow.
For non retina screens the x and y loop can be 1 instead of 0.5

function setup()
    myimage = filledpolygon()
end

function draw()
    background(40, 40, 50)
    sprite(myimage,300,400)
end

function filledpolygon()
    px = {} py = {}      -- x and y coordinates polygon corners
    xmax = 0 ymax = 0
    ----------------------------------------- define polygon --
    fill(255, 0, 214, 255) noStroke()      -- color -----------
    n = 4                                  -- no sides --------
    px[1] = 0        py[1] = 0             -- corner ----------
    px[2] = 100      py[2] = 200           -- corner ----------
    px[3] = 300      py[3] = 50            -- corner ----------
    px[4] = 150      py[4] = 80            -- corner ----------
    -----------------------------------------------------------
    for i = 1,n do if px[i] > xmax then xmax = px[i] end end
    for i = 1,n do if py[i] > ymax then ymax = py[i] end end
    img = image(xmax,ymax)
    setContext(img)
    for x = 0,xmax,0.5 do
    for y = 0,ymax,0.5 do
         j = n oddNodes = false
         for i = 1,n do
            test = false
            if py[i] < y and py[j] >= y then test = true end
            if py[j] < y and py[i] >= y then test = true end
            if test == true then 
                if px[i]+(y-py[i])/(py[j]-py[i])*(px[j]-px[i]) < x then
                    if oddNodes == false then oddNodes = true else oddNodes = false end
                end
            end
            j = i
         end
         if oddNodes == true then rect(x,y,1,1) end
    end
    end
    setContext()
    return img
end

Hope it is usable

Re Peter

2

Refined a bit, so that the corner co-ordinates is passed to the function.
The fill was semi transparent before, so I have changed the size of the small rectangles that is drawn to the image.

here is the function

function drawpolygon(px,py,fr,fg,fb,fa)
    n = 0 for i = 1,100 do if px[i] == nil then break else n = n+1 end end
    xmax = 0 for i = 1,n do if px[i] > xmax then xmax = px[i] end end
    ymax = 0 for i = 1,n do if py[i] > ymax then ymax = py[i] end end
    fill(fr,fg,fb,fa) noStroke()
    img = image(xmax,ymax) setContext(img)
        for x = 0,xmax,0.5 do
            for y = 0,ymax,0.5 do
                j = n odd = false
                for i = 1,n do
                    test = false
                    if py[i] < y and py[j] >= y then test = true end
                    if py[j] < y and py[i] >= y then test = true end
                    if test == true then 
                        if px[i]+(y-py[i])/(py[j]-py[i])*(px[j]-px[i]) < x then
                            if odd == false then odd = true else odd = false end
                        end
                end
                j = i
                end
                if odd == true then rect(x,y,2,2) end
            end
        end
    setContext()
    return img
end

and here a call example (remember in setup() only)

px = {0,100,300,150}
py = {0,200,50,80}
myimage = drawpolygon(px,py,255,0,214,255)

Re Peter

3

@macflyerdk - Zoyt has a better solution

--p is a table of vec2 node positions, c is the colour
function DrawPoly(p,c)
    local m=mesh()
    m.vertices=triangulate(p)
    m:setColors(c)
    return m
end