Shading='flat / nearest / gouraud / phong(?)'

AldoP · March 23, 2022, 6:28pm

Hi there everyone. My name is Aldo and I am an undergrad college student. I am doing a presentation involving some python plot, and different kinds of available shadings.

Since I am fairly new to phython and absolutely new to the matplotlib library, I was wondering if someone could point out where to find the “flat / nearest / gouraud shading” implementation algorithm within the library.

I mean what changes code-side when I declare “shading = flat” in my plot.

Also, if there is any way to implement / simulate “Phong shading”.

I thank you guys in advance for your answers and wish you to keep up with the great work.

QuLogic · January 7, 2023, 6:00am

Flat shading is implemented here

github.com

matplotlib/matplotlib/blob/64fc13a3886c0a7311f915e247deccd8cc84a716/src/_backend_agg.h#L1137


      
                  return (size_t) m_meshWidth * m_meshHeight;
              }
          
          
    inline path_iterator operator()(size_t i) const
              {
                  return QuadMeshPathIterator(i % m_meshWidth, i / m_meshWidth, &m_coordinates);
              }
          };
          
          
template <class CoordinateArray, class OffsetArray, class ColorArray>
          inline void RendererAgg::draw_quad_mesh(GCAgg &gc,
                                                  agg::trans_affine &master_transform,
                                                  unsigned int mesh_width,
                                                  unsigned int mesh_height,
                                                  CoordinateArray &coordinates,
                                                  OffsetArray &offsets,
                                                  agg::trans_affine &offset_trans,
                                                  ColorArray &facecolors,
                                                  bool antialiased,
                                                  ColorArray &edgecolors)
          {

and Gouraud shading here:

github.com

matplotlib/matplotlib/blob/64fc13a3886c0a7311f915e247deccd8cc84a716/src/_backend_agg.h#L1174


      
                                            facecolors,
                                            edgecolors,
                                            linewidths,
                                            linestyles,
                                            antialiaseds,
                                            true, // check_snap
                                            false);
          }
          
          
template <class PointArray, class ColorArray>
          inline void RendererAgg::_draw_gouraud_triangle(PointArray &points,
                                                          ColorArray &colors,
                                                          agg::trans_affine trans,
                                                          bool has_clippath)
          {
              typedef agg::rgba8 color_t;
              typedef agg::span_gouraud_rgba<color_t> span_gen_t;
              typedef agg::span_allocator<color_t> span_alloc_t;
          
          
    trans *= agg::trans_affine_scaling(1.0, -1.0);
              trans *= agg::trans_affine_translation(0.0, (double)height);

I don’t think there’s any implementation of Phong shading.