diff --git a/fractional/src/easel.rs b/fractional/src/easel.rs
index f43535d..1a19379 100644
--- a/fractional/src/easel.rs
+++ b/fractional/src/easel.rs
@@ -21,7 +21,7 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 //
 use std::cmp;
-use std::fmt::{Formatter, Display, Result};
+use std::fmt::{Formatter, Debug, Display, Result};
 use std::ops::{Add, Sub, Div};
 use std::sync::mpsc;
 
@@ -46,6 +46,10 @@ pub trait Drawable<T> {
     fn plot(&self) -> Coordinates<T>;
 }
 
+pub trait Fillable<T> {
+    fn fill(&self) -> Coordinates<T>;
+}
+
 #[derive(Debug, Clone, Copy)]
 pub struct Coordinate<T>(pub i32, pub i32, pub T);
 
@@ -82,15 +86,15 @@ where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
 
         let dx      = (bx - ax).abs();
         let sx :i32 = if ax < bx { 1 } else { -1 };
-        let dy      = -(by - ay).abs();
+        let dy      = (by - ay).abs();
         let sy :i32 = if ay < by { 1 } else { -1 };
-        let size    = cmp::max(dx, -dy);
+        let size    = cmp::max(dx, dy);
         let dz      = (bz - az) / size.into();
 
         let mut v :Vec<Self> = vec!( Coordinate(0, 0, 0.into())
                                    ; (size as usize) + 1);
         v[0] = Coordinate(ax, ay, az);
-        inner(&mut v, bx, by, dx, dy, sx, sy, dz, dx + dy);
+        inner(&mut v, bx, by, dx, -dy, sx, sy, dz, dx - dy);
         v
     }
 }
@@ -258,6 +262,129 @@ where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
     }
 }
 
+impl<T> Fillable<T> for Polygon<T>
+where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
+       + Debug + Clone + Copy + From<i32> {
+    fn fill(&self) -> Coordinates<T> {
+
+        /* bresenham kind of thing to get the outer x values for each y of one
+         * edge of the polygon. */
+        fn walk_edge<T>( a :Coordinate<T>
+                       , b :Coordinate<T> ) -> Vec<Coordinate<T>>
+            where T: Add<Output = T> + Sub<Output = T> + Div<Output = T>
+                   + From<i32> + Debug + Copy {
+
+            let Coordinate(mut x, mut y, mut z) = a;
+            let Coordinate(   bx,    by,    bz) = b;
+
+            // next should be called with the negative of this… but dz depends
+            // on the positive this.
+            let     dy  = -(by - y).abs();
+            let     dx  = (bx - x).abs();
+            let     sx  = if x < bx { 1 } else { -1 };
+            let     dz  = (bz - z) / (-dy).into();
+            let mut err = dx + dy;
+
+            let mut v = Vec::<Coordinate<T>>::with_capacity((-dy) as usize);
+
+            while y != by {
+                match (2*err >= dy, 2*err <= dx) {
+                    (true, false) => { x = x + sx
+                                     ; err = err + dy },
+                    (false, true) => { v.push(Coordinate(x, y, z))
+                                     ; y   = y + 1
+                                     ; z   = z + dz
+                                     ; err = err + dx },
+                    _             => { v.push(Coordinate(x, y, z))
+                                     ; x   = x + sx
+                                     ; y   = y + 1
+                                     ; z   = z + dz
+                                     ; err = err + dx + dy },
+                }
+            }
+
+            v
+        }
+
+        fn next_y<T>( cs :&[Coordinate<T>]
+                    ,  c :usize
+                    ,  f :&dyn Fn(usize) -> usize) -> Option<usize> {
+            fn inner<T>( cs :&[Coordinate<T>]
+                        , c :usize
+                        , n :usize
+                        , f :&dyn Fn(usize) -> usize) -> Option<usize> {
+                if c == n {
+                    None
+                } else {
+                    let Coordinate(_, cy, _) = cs[c];
+                    let Coordinate(_, ny, _) = cs[n];
+
+                    match ny.cmp(&cy) {
+                        cmp::Ordering::Less    => None,
+                        cmp::Ordering::Equal   => inner(cs, c, f(n), f),
+                        cmp::Ordering::Greater => Some(n),
+                    }
+                }
+            }
+
+            inner(cs, c, f(c), f)
+        }
+
+        let Polygon(Coordinates(cs)) = self;
+
+        let vert_min = cs.iter().enumerate()
+                     . fold( None
+                           , |acc, x| match acc {
+                               None    => Some(x),
+                               Some(a) => {
+                                   let Coordinate(_, ay, _) = a.1;
+                                   let Coordinate(_, xy, _) = x.1;
+                                   if xy < ay {Some(x)} else {Some(a)} } } )
+                     . unwrap().0;
+
+        println!("== vert_min: [{:?}] - {:?}", vert_min, cs[vert_min]);
+
+        let right = |x :usize| (x + 1) % cs.len();
+        let left  = |x :usize| if x == 0 { cs.len() - 1 } else { x - 1 };
+
+        let mut r = (vert_min, next_y(cs, vert_min, &right));
+        let mut l = (vert_min, next_y(cs, vert_min, &left));
+
+        let mut l_edge :Vec<Coordinate<T>> = Vec::new();
+        let mut r_edge :Vec<Coordinate<T>> = Vec::new();
+
+        while l.1 != None || r.1 != None {
+            match l.1 {
+                None    => {},
+                Some(a) => {
+                    println!("==        l: [{:?}] - {:?}", l, cs[a]);
+                    l_edge.append(&mut walk_edge(cs[l.0], cs[a]));
+                    l = (a, next_y(cs, a, &left));
+                },
+            }
+
+            match r.1 {
+                None    => {},
+                Some(a) => {
+                    println!("==        r: [{:?}] - {:?}", r, cs[a]);
+                    r_edge.append(&mut walk_edge(cs[r.0], cs[a]));
+                    r = (a, next_y(cs, a, &right));
+                }
+            }
+        }
+
+        println!("== [{}] {:?}", l_edge.len(), l_edge);
+        println!("== [{}] {:?}", r_edge.len(), r_edge);
+
+        // TODO we always miss the last scanline…
+        // TODO check what happend with at least 2 vertices with same y and
+        //      different x…
+        // loop though edges…
+
+        Coordinates(Vec::<Coordinate<T>>::new())
+    }
+}
+
 impl<T> Display for Polygon<T> where T: Copy {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result {
         let Polygon(a) = self;
diff --git a/fractional/src/geometry.rs b/fractional/src/geometry.rs
index 51ce90d..47d0bf0 100644
--- a/fractional/src/geometry.rs
+++ b/fractional/src/geometry.rs
@@ -22,7 +22,7 @@ use std::convert::{From, Into};
 use std::ops::{Add,Sub,Neg,Mul,Div};
 use std::fmt::Debug;
 
-use crate::easel::{Canvas,Coordinate,Coordinates,Polygon};
+use crate::easel::{Canvas,Coordinate,Coordinates,Polygon,Fillable};
 use crate::transform::{TMatrix, Transformable};
 use crate::trigonometry::Trig;
 use crate::vector::Vector;
@@ -347,7 +347,7 @@ where T: Add<Output = T> + Sub<Output = T> + Neg<Output = T>
         // matrix we do not need to do it here.
         let to_coord = |p :&usize| {
             let Point(v, _) = camera.project(self.points[*p]);
-            println!("== {:?} / {:?}", self.points[*p], (v.z() - 1.into()).recip());
+            // println!("== {:?} / {:?}", self.points[*p], (v.z() - 1.into()).recip());
             Coordinate(T::round(&v.x()), T::round(&v.y()), v.z() - 1.into())
         };
         let to_poly  = |f :&Face<T>| {
@@ -361,6 +361,8 @@ where T: Add<Output = T> + Sub<Output = T> + Neg<Output = T>
                                     / (n.mag() * light.dir().mag()),
                        };
 
+                       // this if represents a first simple backface culling
+                       // approach. We only return face that face towards us.
                        if lf < 0.into() {
                            r = r * -lf;
                            g = g * -lf;
@@ -370,14 +372,18 @@ where T: Add<Output = T> + Sub<Output = T> + Neg<Output = T>
                                       | (g.round() as u32) << 8
                                       | (b.round() as u32);
 
+                           (&pg).fill();
+
                            Some((pg, c))
                        } else {
                            None
                        }};
 
-        let mut ps :Vec<(Polygon<T>, u32)> = self.faces.iter()
-                                        . filter_map(to_poly).collect();
-        ps.sort_by(|a, b| a.1.cmp(&b.1));
+        let ps :Vec<(Polygon<T>, u32)> = self.faces.iter()
+                                       . filter_map(to_poly).collect();
+        // this sorts by the color value which is no longer neccessary as soon
+        // as the z-buffer is complete.
+        // ps.sort_by(|a, b| a.1.cmp(&b.1));
         ps
     }
 }