Basic_viewer: color faces by value (distance, cell size, and a drawer value)

BGL/include/CGAL/draw_face_graph.h

@@ -60,6 +60,9 @@ void compute_elements(const FG &fg,
 
   if (gs_options.are_faces_enabled())
   {
+    // Color by value: name the value once, for the legend.
+    if (!gs_options.face_value_name.empty())
+    { graphics_scene.set_value_name(gs_options.face_value_name); }
     for (auto fh : faces(fg))
     {
       if (fh != boost::graph_traits<FG>::null_face() && // face exists
@@ -78,6 +81,9 @@ void compute_elements(const FG &fg,
           hd = next(hd, fg);
         }
         while (hd != first_hd);
+        // Color by value: attach the face's scalar value before committing it.
+        if (gs_options.is_face_valued(fg, fh))
+        { graphics_scene.set_face_value(gs_options.face_value(fg, fh)); }
         graphics_scene.face_end();
       }
     }

Basic_viewer/doc/Basic_viewer/Concepts/GraphicsSceneOptions.h

@@ -75,6 +75,17 @@ class GraphicsSceneOptions
   /// `nullptr` by default.
   std::function<CGAL::IO::Color(const DS &, face_descriptor)> face_color;
 
+  /// `std::function` that returns `true` when call for faces having an associated a scalar value, and `false` otherwise. `false` by default.
+  std::function<bool(const DS &, face_descriptor)> is_face_valued;
+
+  /// `std::function` that returns the associated scalar value of a face. Called only if
+  /// `is_face_valued()` returns `true`. The viewer normalizes the values over their range
+  /// and maps them to a color palette.
+  std::function<float(const DS &, face_descriptor)> face_value;
+
+  /// name of the value, shown in the viewer's color legend (for example "aspect ratio").
+  std::string face_value_name;
+
   /// ignores all vertices when `b` is `true`; otherwise ignores only vertices for which `ignore_vertex()` returns `true`.
   void ignore_all_vertices(bool b);
 

Basic_viewer/include/CGAL/Basic_shaders.h

@@ -75,6 +75,38 @@ uniform highp   vec4  u_PointPlane;
 uniform mediump float u_RenderingMode;
 uniform mediump float u_RenderingTransparency;
 
+// Color by value: 0 keeps the vertex color, otherwise a palette index. The
+// value shown is the signed distance from the fragment to the clipping plane,
+// normalised to [u_ValueMin, u_ValueMax].
+uniform mediump float u_ColorMapMode;
+uniform mediump float u_ValueMin;
+uniform mediump float u_ValueMax;
+// Per cell: the viewer gives one value for the whole cell (its centre distance or
+// its size), so a whole cell takes one flat color and neighbouring cells do not melt.
+uniform int           u_ColorPerCell;
+uniform highp   float u_CellValue;
+
+vec3 color_palette(float t, float mode)
+{
+  if (mode < 1.5)
+  { return clamp(vec3(t*3.0, t*3.0-1.0, t*3.0-2.0), 0.0, 1.0); } // heat
+  if (mode < 2.5)
+  { return clamp(vec3(1.5-abs(4.0*t-3.0), 1.5-abs(4.0*t-2.0), 1.5-abs(4.0*t-1.0)),
+                 0.0, 1.0); } // jet
+  if (mode < 3.5)
+  { return vec3(t); } // grey ramp
+  // viridis, a perceptually uniform map (polynomial fit by Matt Zucker). The same
+  // coefficients are mirrored in the viewer's legend so the bar matches the faces.
+  const vec3 c0=vec3(0.2777273272234177, 0.005407344544966578, 0.3340998053353061);
+  const vec3 c1=vec3(0.1050930431085774, 1.404613529898575, 1.384590162594685);
+  const vec3 c2=vec3(-0.3308618287255563, 0.214847559468213, 0.09509516302823659);
+  const vec3 c3=vec3(-4.634230498983486, -5.799100973351585, -19.33244095627987);
+  const vec3 c4=vec3(6.228269936347081, 14.17993336680509, 56.69055260068105);
+  const vec3 c5=vec3(4.776384997670288, -13.74514537774601, -65.35303263337234);
+  const vec3 c6=vec3(-5.435455855934631, 4.645852612178535, 26.3124352495832);
+  return clamp(c0+t*(c1+t*(c2+t*(c3+t*(c4+t*(c5+t*c6))))), 0.0, 1.0);
+}
+
 void main(void)
 {
   highp vec3 L = u_LightPos.xyz - vs_fP.xyz;
@@ -84,9 +116,19 @@ void main(void)
   L = normalize(L);
   V = normalize(V);
 
+  // Base color is the vertex color, or a palette applied to the value.
+  vec3 base = fColor.rgb;
+  if (u_ColorMapMode > 0.5)
+  {
+    float value = (u_ColorPerCell != 0) ? u_CellValue
+                : dot(ls_fP.xyz-u_PointPlane.xyz, normalize(u_ClipPlane.xyz));
+    float t = clamp((value-u_ValueMin)/max(u_ValueMax-u_ValueMin, 1e-6), 0.0, 1.0);
+    base = color_palette(t, u_ColorMapMode);
+  }
+
   highp vec3 R = reflect(-L, a_Normal);
-  highp vec4 diffuse = vec4(max(dot(a_Normal,L), 0.0) * u_LightDiff.rgb * fColor.rgb, 1.0);
-  highp vec4 ambient = vec4(u_LightAmb.rgb * fColor.rgb, 1.0);
+  highp vec4 diffuse = vec4(max(dot(a_Normal,L), 0.0) * u_LightDiff.rgb * base, 1.0);
+  highp vec4 ambient = vec4(u_LightAmb.rgb * base, 1.0);
   highp vec4 specular = pow(max(dot(R,V), 0.0), u_SpecPower) * u_LightSpec;
 
   // onPlane == 1: inside clipping plane, should be solid;

Basic_viewer/include/CGAL/Graphics_scene.h

@@ -252,6 +252,13 @@ class Graphics_scene
     return m_buffer_for_faces.is_a_face_started();
   }
 
+  /// sets the scalar value of the face currently being built. The viewer can color
+  /// the faces by these values, normalised over their range and mapped to a palette.
+  void set_face_value(float v) { m_current_face_value=v; m_has_face_values=true; }
+
+  /// sets the name of the value, shown in the viewer's color legend.
+  void set_value_name(const std::string &n) { m_value_name=n; }
+
   void face_begin()
   {
     if (a_face_started())
@@ -314,6 +321,7 @@ class Graphics_scene
         const unsigned int idx=static_cast<unsigned int>(m_faces.size());
         m_faces.emplace_back(m_current_face_start,
                              number_of_elements(POS_FACES)-m_current_face_start);
+        record_current_face_value();
         m_face_dedup.emplace(std::move(key), idx);
         m_volume_faces.back().push_back(idx);
         return;
@@ -324,6 +332,22 @@ class Graphics_scene
     // Record this face's vertex range in POS_FACES, for the clip-plane cap.
     m_faces.emplace_back(m_current_face_start,
                          number_of_elements(POS_FACES) - m_current_face_start);
+    record_current_face_value();
+  }
+
+  // Color by value: store the value of the face just committed, parallel to
+  // m_faces, and keep the min and max for the palette range.
+  void record_current_face_value()
+  {
+    if (m_has_face_values)
+    {
+      if (m_face_values.empty())
+      { m_face_value_min=m_face_value_max=m_current_face_value; }
+      else
+      { if (m_current_face_value<m_face_value_min) { m_face_value_min=m_current_face_value; }
+        if (m_current_face_value>m_face_value_max) { m_face_value_max=m_current_face_value; } }
+    }
+    m_face_values.push_back(m_current_face_value);
   }
 
   // Clip-plane cap: a volume groups the faces added until volume_end, de-duplicated
@@ -366,6 +390,14 @@ class Graphics_scene
   const std::vector<CGAL::Bbox_3> &get_volume_bboxes() const
   { return m_volume_bboxes; }
 
+  // Color by value: the per-face values set by the drawer, whether any were set,
+  // the legend name, and the value range.
+  const std::vector<float> &get_face_values() const { return m_face_values; }
+  bool has_face_values() const { return m_has_face_values; }
+  const std::string &value_name() const { return m_value_name; }
+  float face_value_min() const { return m_face_value_min; }
+  float face_value_max() const { return m_face_value_max; }
+
   template <typename KPoint>
   void add_text(const KPoint &kp, const std::string &txt)
   {
@@ -509,6 +541,16 @@ class Graphics_scene
   std::vector<CGAL::Bbox_3> m_volume_bboxes;
   unsigned int m_current_face_start = 0;
 
+  // Color by value: an optional scalar per face, set by the drawer, that the viewer
+  // maps to a palette (like the color, but any float). Each value is parallel to
+  // m_faces; m_value_name labels the legend.
+  std::vector<float> m_face_values;
+  float m_current_face_value = 0.f;
+  bool m_has_face_values = false;
+  std::string m_value_name;
+  float m_face_value_min = 0.f;
+  float m_face_value_max = 1.f;
+
   // Clip-plane cap: geometric face de-duplication during volume building. The key
   // is the sorted face vertex positions, so both sides of a shared wall match.
   // Hashed so the build stays linear on meshes with many faces.

Basic_viewer/include/CGAL/Graphics_scene_options.h

@@ -52,6 +52,8 @@ struct Graphics_scene_options<DS, VertexDescriptor, EdgeDescriptor, FaceDescript
     colored_face=[](const DS &, face_descriptor)->bool { return false; };
 
     face_wireframe=[](const DS &, face_descriptor)->bool { return false; };
+
+    is_face_valued=[](const DS &, face_descriptor)->bool { return false; };
   }
 
   // The seven following functions should not be null
@@ -65,6 +67,19 @@ struct Graphics_scene_options<DS, VertexDescriptor, EdgeDescriptor, FaceDescript
 
   std::function<bool(const DS &, face_descriptor)> face_wireframe;
 
+  /// `std::function` that returns `true` if the given face carries a scalar value to
+  /// color it by, `false` otherwise. `false` by default.
+  std::function<bool(const DS &, face_descriptor)>  is_face_valued;
+
+  /// `std::function` that returns the scalar value of the given face. Called only
+  /// when `is_face_valued()` returns `true`. The viewer normalises the values over their
+  /// range and maps them to a color palette.
+  std::function<float(const DS &, face_descriptor)> face_value;
+
+  /// The name of the value, shown in the viewer's color legend (for example
+  /// "aspect ratio"). Empty by default.
+  std::string face_value_name;
+
   // These functions must be non null if the corresponding colored_XXX function
   // returns true.
   std::function<CGAL::IO::Color(const DS &, vertex_descriptor)> vertex_color;