How can you code a filled polygon that isn't a circle or rectangle?

EatMoreCheese • 2016-12-26*2016-12-26 17:01* •

Hey I'm looking for a simple way to draw a filled shape that isn't one of the standard shapes. For example, a pizza slice or a large triangle.

Any suggestions? I can draw the outline okay but I want it filled.

solar • 2016-12-26*2016-12-26 18:43*

You're gonna want a "trifill" function, there isn't one included with Pico8. There have been a few floating around the forums here, the first one that comes to mind is part of electric gryphon's 3D engine library.

There's a function in there called solid_trifill(). It shouldn't be too hard to extract that from the code if you just want to use that by itself...

https://www.lexaloffle.com/bbs/?tid=28077

That function in itself can only draw a triangle, to construct anything more complex you'd have to call it multiple times, piecing the shape together from triangles.

EDIT: Or there's the post below!!

scgrn • 2016-12-26*2016-12-26 18:56*

Here's my polyfill code:

-- draws a filled convex polygon
-- v is an array of vertices
-- {x1, y1, x2, y2} etc
function render_poly(v,col)
 col=col or 5

 -- initialize scan extents
 -- with ludicrous values
 local x1,x2={},{}
 for y=0,127 do
  x1[y],x2[y]=128,-1
 end
 local y1,y2=128,-1

 -- scan convert each pair
 -- of vertices
 for i=1, #v/2 do
  local next=i+1
  if (next>#v/2) next=1

  -- alias verts from array
  local vx1=flr(v[i*2-1])
  local vy1=flr(v[i*2])
  local vx2=flr(v[next*2-1])
  local vy2=flr(v[next*2])

  if vy1>vy2 then
   -- swap verts
   local tempx,tempy=vx1,vy1
   vx1,vy1=vx2,vy2
   vx2,vy2=tempx,tempy
  end 

  -- skip horizontal edges and
  -- offscreen polys
  if vy1~=vy2 and vy1<128 and
   vy2>=0 then

   -- clip edge to screen bounds
   if vy1<0 then
    vx1=(0-vy1)*(vx2-vx1)/(vy2-vy1)+vx1
    vy1=0
   end
   if vy2>127 then
    vx2=(127-vy1)*(vx2-vx1)/(vy2-vy1)+vx1
    vy2=127
   end

   -- iterate horizontal scans
   for y=vy1,vy2 do
    if (y<y1) y1=y
    if (y>y2) y2=y

    -- calculate the x coord for
    -- this y coord using math!
    x=(y-vy1)*(vx2-vx1)/(vy2-vy1)+vx1

    if (x<x1[y]) x1[y]=x
    if (x>x2[y]) x2[y]=x
   end 
  end
 end

 -- render scans
 for y=y1,y2 do
  local sx1=flr(max(0,x1[y]))
  local sx2=flr(min(127,x2[y]))

  local c=col*16+col
  local ofs1=flr((sx1+1)/2)
  local ofs2=flr((sx2+1)/2)
  memset(0x6000+(y*64)+ofs1,c,ofs2-ofs1)
  pset(sx1,y,c)
  pset(sx2,y,c)
 end 
end