Add a Viewer option to use a specif shader to make more obvious the orientation of the fragments in the shaded programs.

Polyhedron/demo/Polyhedron/MainWindow.cpp

@@ -2275,6 +2275,11 @@ void MainWindow::on_actionPreferences_triggered()
     this->s_defaultPSRM = CGAL::Three::Three::modeFromName(text);
   });
   
+  connect(prefdiag.backFrontColor_pushButton, &QPushButton::clicked,
+          this, [this](){
+    qobject_cast<Viewer*>(CGAL::Three::Three::activeViewer())->setBackFrontColors();
+  });
+
   std::vector<QTreeWidgetItem*> items;
   QBrush successBrush(Qt::green),
       errorBrush(Qt::red),
@@ -2959,6 +2964,9 @@ void MainWindow::setupViewer(Viewer* viewer, SubViewer* subviewer)
     }
     viewer->setTotalPass(nb);
   });
+  action= subviewer->findChild<QAction*>("actionBackFrontShading");
+  connect(action, SIGNAL(toggled(bool)),
+          viewer, SLOT(setBackFrontShading(bool)));
   connect(viewer, SIGNAL(requestContextMenu(QPoint)),
           this, SLOT(contextMenuRequested(QPoint)));
   connect(viewer, SIGNAL(selected(int)),
@@ -3127,6 +3135,11 @@ SubViewer::SubViewer(QWidget *parent, MainWindow* mw, Viewer* mainviewer)
   QAction* actionTotalPass = new QAction("Set Transparency Pass &Number...",this);
   actionTotalPass->setObjectName("actionTotalPass");
   viewMenu->addAction(actionTotalPass);
+  QAction* actionBackFrontShading = new QAction("Activate Back/Front shading.",this);
+  actionBackFrontShading->setObjectName("actionBackFrontShading");
+  actionBackFrontShading->setCheckable(true);
+  actionBackFrontShading->setChecked(false);
+  viewMenu->addAction(actionBackFrontShading);
   if(mainviewer)
     setAttribute(Qt::WA_DeleteOnClose);
   setWindowIcon(QIcon(":/cgal/icons/resources/menu.png"));

Polyhedron/demo/Polyhedron/Preferences.ui

@@ -58,9 +58,9 @@
            <property name="geometry">
             <rect>
              <x>0</x>
-             <y>0</y>
+             <y>-96</y>
-             <width>278</width>
+             <width>275</width>
-             <height>499</height>
+             <height>528</height>
             </rect>
            </property>
            <layout class="QVBoxLayout" name="verticalLayout_3">
@@ -285,6 +285,13 @@
               </property>
              </widget>
             </item>
+            <item>
+             <widget class="QPushButton" name="backFrontColor_pushButton">
+              <property name="text">
+               <string>Change Back/Front Colors...</string>
+              </property>
+             </widget>
+            </item>
             <item>
              <spacer name="verticalSpacer">
               <property name="orientation">

Polyhedron/demo/Polyhedron/Viewer.cpp

@@ -51,6 +51,10 @@ public:
   QVector4D specular;
   float spec_power;
 
+  //Back and Front Colors
+  QColor front_color;
+  QColor back_color;
+  
   // M e s s a g e s
   QString message;
   bool _displayMessage;
@@ -251,11 +255,22 @@ void Viewer::doBindings()
                           specular.split(",").at(2).toFloat(),
                           1.0f);
 
+  QString front_color = viewer_settings.value("front_color", QString("1.0,0.0,0.0")).toString();
+  d->front_color= QColor(255*front_color.split(",").at(0).toFloat(),
+                         255*front_color.split(",").at(1).toFloat(),
+                         255*front_color.split(",").at(2).toFloat(),
+                         1.0f);
+  QString back_color = viewer_settings.value("back_color", QString("0.0,0.0,1.0")).toString();
+  d->back_color= QColor( 255*back_color.split(",").at(0).toFloat(),
+                         255*back_color.split(",").at(1).toFloat(),
+                         255*back_color.split(",").at(2).toFloat(),
+                         1.0f);
   d->spec_power = viewer_settings.value("spec_power", 51.8).toFloat();
   d->scene = 0;
   d->projection_is_ortho = false;
   d->twosides = false;
   this->setProperty("draw_two_sides", false);
+  this->setProperty("back_front_shading", false);
   d->macro_mode = false;
   d->inFastDrawing = true;
   d->inDrawWithNames = false;
@@ -333,6 +348,7 @@ Viewer::Viewer(QWidget* parent,
   is_sharing = true;
   d->antialiasing = antialiasing;
   this->setProperty("draw_two_sides", false);
+  this->setProperty("back_front_shading", false);
   this->setProperty("helpText", QString("This is a sub-viewer. It displays the scene "
                                         "from another point of view. \n "));
   is_ogl_4_3 = sharedWidget->is_ogl_4_3;
@@ -367,6 +383,17 @@ Viewer::~Viewer()
                              .arg(d->specular.z()));
     viewer_settings.setValue("spec_power",
                              d->spec_power);
+    viewer_settings.setValue("front_color",
+                             QString("%1,%2,%3")
+                             .arg(d->front_color.redF())
+                             .arg(d->front_color.greenF())
+                             .arg(d->front_color.blueF()));
+    viewer_settings.setValue("back_color",
+                             QString("%1,%2,%3")
+                             .arg(d->back_color.redF())
+                             .arg(d->back_color.greenF())
+                             .arg(d->back_color.blueF()));
+
     if(d->_recentFunctions)
       delete d->_recentFunctions;
     if(d->painter)
@@ -401,6 +428,13 @@ void Viewer::setTwoSides(bool b)
 }
 
 
+void Viewer::setBackFrontShading(bool b)
+{
+  this->setProperty("back_front_shading", b);
+  update();
+}
+
+
 void Viewer::setFastDrawing(bool b)
 {
   d->inFastDrawing = b;
@@ -947,7 +981,10 @@ void Viewer::attribBuffers(int program_name) const {
         program->setUniformValue("light_spec", d->specular);
         program->setUniformValue("light_amb", d->ambient);
         program->setUniformValue("spec_power", d->spec_power);
+        program->setUniformValue("front_color", d->front_color);
+        program->setUniformValue("back_color", d->back_color);
         program->setUniformValue("is_two_side", d->twosides);
+        program->setUniformValue("back_front_shading", this->property("back_front_shading").toBool());
         break;
     }
     switch(program_name)
@@ -1805,6 +1842,65 @@ void Viewer::setLighting()
   }
 }
 
+void Viewer::setBackFrontColors()
+{
+
+  //save current settings;
+
+  QColor prev_front_color = d->front_color;
+  QColor prev_back_color = d->back_color;
+  QDialog *dialog = new QDialog(this);
+  QDialogButtonBox* buttonBox = new QDialogButtonBox(QDialogButtonBox::Ok
+                                   | QDialogButtonBox::Cancel, dialog);
+
+  connect(buttonBox, &QDialogButtonBox::accepted, dialog, &QDialog::accept);
+  connect(buttonBox, &QDialogButtonBox::rejected, dialog, &QDialog::reject);
+
+  QGridLayout* layout = new QGridLayout(dialog);
+  layout->addWidget(new QLabel("Front color: ",dialog),0,0);
+  QPalette front_palette;
+  front_palette.setColor(QPalette::Button, d->front_color);
+  QPushButton* frontButton = new QPushButton(dialog);
+  frontButton->setPalette(front_palette);
+  QPalette back_palette;
+  back_palette.setColor(QPalette::Button, d->back_color);
+  QPushButton* backButton = new QPushButton(dialog);
+  backButton->setPalette(back_palette);
+  layout->addWidget(frontButton,0,1);
+  layout->addWidget(new QLabel("Back color: ",dialog),1,0);
+  layout->addWidget(backButton,1,1);
+  layout->addWidget(buttonBox);
+  dialog->setLayout(layout);
+  connect(frontButton, &QPushButton::clicked,
+          [this, dialog, frontButton](){
+    QColorDialog *color_dial = new QColorDialog(dialog);
+    color_dial->exec();
+    QColor front_color = color_dial->selectedColor();
+    QPalette palette;
+    palette.setColor(QPalette::Button, front_color);
+    frontButton->setPalette(palette);
+    d->front_color= front_color;
+  });
+  connect(backButton, &QPushButton::clicked,
+          [this, dialog, backButton](){
+    QColorDialog *color_dial = new QColorDialog(dialog);
+    color_dial->exec();
+    QColor back_color = color_dial->selectedColor();
+    QPalette palette;
+    palette.setColor(QPalette::Button, back_color);
+    backButton->setPalette(palette);
+    d->back_color= back_color;
+
+  });
+  if(!dialog->exec())
+  {
+    //restore previous settings
+    d->front_color= prev_front_color;
+    d->back_color= prev_back_color;
+    return;
+  }
+}
+
 void Viewer::setGlPointSize(const GLfloat &p) { d->gl_point_size = p; }
 
 const GLfloat& Viewer::getGlPointSize() const { return d->gl_point_size; }

Polyhedron/demo/Polyhedron/Viewer.h

@@ -101,6 +101,7 @@ public Q_SLOTS:
   //! If b is true, facets will be ligted from both internal and external sides.
   //! If b is false, only the side that is exposed to the light source will be lighted.
   void setTwoSides(bool b) Q_DECL_OVERRIDE;
+  void setBackFrontShading(bool b) Q_DECL_OVERRIDE;
   void SetOrthoProjection( bool b) Q_DECL_OVERRIDE;
   //! If b is true, some items are displayed in a simplified version when moving the camera.
   //! If b is false, items display is never altered, even when moving.
@@ -127,6 +128,7 @@ public Q_SLOTS:
   }
 
   void setLighting();
+  void setBackFrontColors();
 
   void messageLogged(QOpenGLDebugMessage);
 

Polyhedron/demo/Polyhedron/resources/compatibility_shaders/shader_with_light.frag

@@ -3,6 +3,8 @@ varying highp vec4 color;
 varying highp vec4 fP;
 varying highp vec3 fN;
 varying highp float dist[6];
+uniform highp vec4 front_color;
+uniform highp vec4 back_color;
 uniform highp vec4 light_pos;
 uniform highp vec4 light_diff;
 uniform highp vec4 light_spec;
@@ -17,6 +19,7 @@ uniform highp float width;
 uniform highp float height;
 uniform bool comparing;
 uniform bool writing;
+uniform bool back_front_shading;
 uniform sampler2D sampler;
 uniform highp float alpha;
 
@@ -44,7 +47,6 @@ void main(void) {
     gl_FragColor = vec4(d,d,d,1.0);
   else
   {
-    highp vec4 my_color = vec4(color.xyz, 1.0);
     highp vec3 L = light_pos.xyz - fP.xyz;
     highp vec3 V = -fP.xyz;
     highp vec3 N;
@@ -56,6 +58,19 @@ void main(void) {
     V = normalize(V);
     highp vec3 R = reflect(-L, N);
     highp vec4 diffuse;
+    float dot_prod = dot(N,L);
+    highp vec4 my_color;
+    if(back_front_shading)
+    {
+      if (dot_prod > 0)
+        my_color = front_color;
+      else
+        my_color = back_color;
+    }
+    else
+    {
+      my_color = highp vec4(color.xyz, 1.0);
+    }
     if(is_two_side == 1)
       diffuse = abs(dot(N,L)) * light_diff * color;
     else

Polyhedron/demo/Polyhedron/resources/shader_with_light.frag

@@ -3,6 +3,8 @@ in vec4 color;
 in vec4 fP;
 in vec3 fN;
 in float dist[6];
+uniform vec4 front_color;
+uniform vec4 back_color;
 uniform vec4 light_pos;
 uniform vec4 light_diff;
 uniform vec4 light_spec;
@@ -17,6 +19,7 @@ uniform float width;
 uniform float height;
 uniform bool comparing;
 uniform bool writing;
+uniform bool back_front_shading;
 uniform sampler2D sampler;
 uniform float alpha;
 out vec4 out_color;
@@ -45,7 +48,6 @@ void main(void) {
     out_color = vec4(d,d,d,1.0);
   else
   {
-    vec4 my_color = vec4(color.xyz, 1.0);
     vec3 L = light_pos.xyz - fP.xyz;
     vec3 V = -fP.xyz;
     vec3 N;
@@ -57,10 +59,24 @@ void main(void) {
     V = normalize(V);
     vec3 R = reflect(-L, N);
     vec4 diffuse;
-    if(is_two_side == 1)
+    float dot_prod = dot(N,L);
-      diffuse = abs(dot(N,L)) * light_diff * color;
+    vec4 my_color;
+    if(back_front_shading)
+    {
+      if (dot_prod > 0)
+        my_color = front_color;
+      else
+        my_color = back_color;
+    }
     else
-      diffuse = max(dot(N,L), 0.0) * light_diff * my_color;
+    {
+      my_color = vec4(color.xyz, 1.0);
+    }
+    if(is_two_side == 1)
+      diffuse = abs(dot_prod) * light_diff * color;
+    else
+      diffuse = max(dot_prod, 0.0) * light_diff * my_color;
+
     vec4 specular = pow(max(dot(R,V), 0.0), spec_power) * light_spec;
     vec4 ret_color = vec4((my_color*light_amb).xyz + diffuse.xyz + specular.xyz,1);
     if(is_selected)

Three/include/CGAL/Three/Viewer_interface.h

@@ -238,6 +238,9 @@ public Q_SLOTS:
   //! If b is true, faces will be ligted from both internal and external side.
   //! If b is false, only the side that is exposed to the light source will be lighted.
   virtual void setTwoSides(bool b) = 0;
+  //! If b is true, then a special color mask is applied to points and meshes to differenciate
+  //! front-faced and back-faced elements.
+  virtual void setBackFrontShading(bool b) =0;
   //! \brief Sets the fast drawing mode
   //! @see inFastDrawing()
   virtual void setFastDrawing(bool b) = 0;