Made the perspective display resort the points with the proper z order

whenever you release the mouse button or add more points.

dlib/gui_widgets/widgets.cpp

@@ -5722,12 +5722,15 @@ namespace dlib
             max_pts.z() = std::max(overlay[i].p2.z(), max_pts.z());
         }
 
+        dot_sorting_is_stale = true;
         tform = camera_transform(max_pts,
             sum_pts/(overlay_lines.size()*2+overlay_dots.size()),
             vector<double>(0,0,1),
             tform.get_camera_field_of_view(),
             std::min(rect.width(),rect.height()));
 
+        sort_dots();
+
         // make the parent window redraw us now that we changed the overlay
         parent.invalidate_rectangle(rect);
     }
@@ -5743,17 +5746,17 @@ namespace dlib
         if (overlay.size() == 0)
             return;
 
-        // push this new overlay into our overlay vector
-        overlay_dots.insert(overlay_dots.end(), overlay.begin(), overlay.end());
-
         for (unsigned long i = 0; i < overlay.size(); ++i)
         {
+            overlay_dots.push_back(std::make_pair(overlay[i], 0));
+
             sum_pts += overlay[i].p;
             max_pts.x() = std::max(overlay[i].p.x(), max_pts.x());
             max_pts.y() = std::max(overlay[i].p.y(), max_pts.y());
             max_pts.z() = std::max(overlay[i].p.z(), max_pts.z());
         }
 
+        dot_sorting_is_stale = true;
         tform = camera_transform(max_pts,
             sum_pts/(overlay_lines.size()*2+overlay_dots.size()),
             vector<double>(0,0,1),
@@ -5811,9 +5814,9 @@ namespace dlib
         }
         for (unsigned long i = 0; i < overlay_dots.size(); ++i)
         {
-            point p = tform(overlay_dots[i].p) + rect.tl_corner();
+            point p = tform(overlay_dots[i].first.p) + rect.tl_corner();
             if (area.contains(p))
-                assign_pixel(c[p.y()-c.top()][p.x()-c.left()], overlay_dots[i].color);
+                assign_pixel(c[p.y()-c.top()][p.x()-c.left()], overlay_dots[i].first.color);
         }
 
     }
@@ -5882,7 +5885,7 @@ namespace dlib
             const dpoint pp(x,y);
             for (unsigned long i = 0; i < overlay_dots.size(); ++i)
             {
-                dpoint p = tform(overlay_dots[i].p) + rect.tl_corner();
+                dpoint p = tform(overlay_dots[i].first.p) + rect.tl_corner();
                 double dist = length_squared(p-pp);
                 if (dist < best_dist)
                 {
@@ -5891,7 +5894,43 @@ namespace dlib
                 }
             }
             if (dot_clicked_event_handler.is_set())
-                dot_clicked_event_handler(overlay_dots[best_idx].p);
+                dot_clicked_event_handler(overlay_dots[best_idx].first.p);
+        }
+    }
+
+// ----------------------------------------------------------------------------------------
+
+    void perspective_display::
+    sort_dots (
+    )
+    {
+        if (dot_sorting_is_stale)
+        {
+            // sort the dots so that the dots farthest from the camera are drawn first.
+            // We begin by updating the distance from each dot to the camera.
+            const vector<double> cam = tform.get_camera_pos();
+            for (unsigned long i = 0; i < overlay_dots.size(); ++i)
+                overlay_dots[i].second = length_squared(overlay_dots[i].first.p-cam);
+            std::sort(overlay_dots.rbegin(), overlay_dots.rend(), compare_second);
+
+            dot_sorting_is_stale = false;
+            parent.invalidate_rectangle(rect);
+        }
+    }
+
+// ----------------------------------------------------------------------------------------
+
+    void perspective_display::
+    on_mouse_up (
+        unsigned long,// btn,
+        unsigned long,// state,
+        long,// x,
+        long// y
+    )
+    {
+        if (!hidden && enabled && overlay_dots.size() != 0)
+        {
+            sort_dots();
         }
     }
 
@@ -5922,6 +5961,7 @@ namespace dlib
             // now make it have the correct radius relative to the looking at point.
             new_pos = (new_pos-tform.get_camera_looking_at()).normalize()*length(radius) + tform.get_camera_looking_at();
 
+            dot_sorting_is_stale = true;
             tform = camera_transform(new_pos,
                 tform.get_camera_looking_at(),
                 tangent_y,
@@ -5944,6 +5984,7 @@ namespace dlib
             vector<double> offset = tangent_x*delta.x() + tangent_y*-delta.y(); 
 
 
+            dot_sorting_is_stale = true;
             tform = camera_transform(
                 tform.get_camera_pos()+offset,
                 tform.get_camera_looking_at()+offset,

dlib/gui_widgets/widgets.h

@@ -3706,20 +3706,35 @@ namespace dlib
             bool is_double_click
         );
 
+        void on_mouse_up (
+            unsigned long btn,
+            unsigned long state,
+            long x,
+            long y
+        );
+
         void on_mouse_move (
             unsigned long state,
             long x,
             long y
         );
 
+        static bool compare_second (
+            const std::pair<overlay_dot,float>& a,
+            const std::pair<overlay_dot,float>& b
+        ) { return a.second < b.second; }
+
+        void sort_dots();
+
         point last;
         std::vector<overlay_line> overlay_lines;
-        std::vector<overlay_dot> overlay_dots;
+        std::vector<std::pair<overlay_dot,float> > overlay_dots;
 
         camera_transform tform;
         vector<double> sum_pts;
         vector<double> max_pts;
         any_function<void(const vector<double>&)> dot_clicked_event_handler;
+        bool dot_sorting_is_stale;
     };
 
 // ----------------------------------------------------------------------------------------