Re: Problems with outline rasterizer

> I noticed that the outline rasterizer fails to draw empty (or
> nearly-empty) rectangles. For example, consider a rectangle with vertices
> ABCD and zero height. The sequence of events goes like this:
>
> 1) Add vertex A to path. Vertex list is now "A".
>
> 2) Add vertex B to path. Vertex list is now "AB".
>
> 3) Add vertex C to path - A and B are coincident so vertex B is removed.
> Vertex list is now "AC".
>
> 4) Add vertex D to path. Vertex list is now "ACD".
>
> 5) Process path_cmd_end_poly:
>  - rasterizer_outline_aa<>::render closes the path
>  - vertex_sequence<>::close sees that C and D are coincident and removes
>  vertex C
>  - Vertex list is now "AD"
>  - rasterizer_outline_aa<>::render no-ops because vertex count < 3
>
> I propose changing the logic in rasterizer_outline_aa<>::render from this:
>
>   if(close_polygon)
>   {
>     if(m_src_vertices.size() >= 3)
>     {
>        // ...
>     }
>   }
>   else
>   // ...
>
> to this:
>
>   if(close_polygon && (m_src_vertices.size() >= 3))
>   {
>     // ...
>   }
>   else
>   // ...
>
> Now the zero-height rectangle will be drawn as a line. Does this seem
> like a reasonable fix, or might it cause other problems?
>
> Also, the outline rasterizer will "optimize" away rectangles with
> single-pixel width/height, because it considers points at a distance of
> 1.5 times the subpixel scale or closer to be coincident. Presumably Maxim
> had a reason for choosing this threshold, but I propose changing
> line_aa_vertex::operator() from this:
>
>   bool operator () (const line_aa_vertex& val)
>   {
>     float_type dx = val.x - x;
>     float_type dy = val.y - y;
>     return (len = uround(sqrt(dx * dx + dy * dy))) >
>       (line_subpixel_scale + line_subpixel_scale / 2);
>   }
>
> to this:
>
>   bool operator () (const line_aa_vertex& val)
>   {
>     float_type dx = val.x - x;
>     float_type dy = val.y - y;
>     return (len = uround(sqrt(dx * dx + dy * dy))) >= line_subpixel_scale;
>   }
>
> Comments?