--- t/example.cc~	2020-02-24 14:44:49.787613251 +0200
+++ t/example.cc	2020-06-29 01:28:50.315006837 +0300
@@ -8,14 +8,14 @@
     float begin, step;
 public:
     Slope() {}
-    Slope(float from, float to, int num_steps)
+    Slope(float from, float to, float num_steps)
     {
         float inv_step = 1.f / num_steps;
         begin = from;                   // Begin here
         step  = (to - from) * inv_step; // Stepsize = (end-begin) / num_steps
     }
-    float get() const { return begin; }
-    void advance()    { begin += step; }
+    float get() const       { return begin; }
+    void advance(float n=1) { begin += step*n; }
 };
 
 template<typename PlotFunc, typename T, std::size_t Size = std::tuple_size_v<T>>
@@ -49,16 +49,18 @@
         // Scanline function
         [&](int y, SlopeData& left, SlopeData& right)
         {
-            int x = left[0].get(), endx = right[0].get();
+            float leftx = left[0].get(), endx = right[0].get();
+            auto intleftx = std::floor(leftx+.5f), rounding_error = intleftx - leftx + .5f;
 
             // Number of steps = number of pixels on this scanline = endx-x
             std::array<Slope, Size-2> props;
             for(unsigned p=0; p<Size-2; ++p)
             {
-                props[p] = Slope( left[p+1].get(), right[p+1].get(), endx-x );
+                props[p] = Slope( left[p+1].get(), right[p+1].get(), endx-leftx );
+                props[p].advance(rounding_error);
             }
 
-            for(; x < endx; ++x) // Render each pixel
+            for(int x = intleftx, e = endx+.5f; x < e; ++x) // Render each pixel
             {
                 std::apply([&](auto... args) { Plot(x,y, args.get()...); }, props);