Minor tweak to NavMesh

examples/cray_eye.cpp

@@ -27,11 +27,12 @@ int main (int argc, char** argv)
         eyefile = std::string (argv[1]);
     }
 
+    // Compound eyes are tiny. We make them larger in our scene by this factor
+    constexpr float eye_scaleup = 1000.0f;
+
     float psrad = 0.5f;
     if (argc > 2) { psrad = std::atof (argv[2]); }
 
-    auto v = mplot::Visual<>(1024, 768, "mplot::compoundray::EyeVisual");
-
     // We read the information from the eye file into a vector of Ommatidium objects.  Ommatidium is
     // defined in "cameras/CompoundEyeDataTypes.h" in compound ray, mplot::Ommatidium is a
     // mplot/Seb's maths style equivalent. It contains 2 3D float vectors and two scalar floating point
@@ -43,6 +44,18 @@ int main (int argc, char** argv)
     // using it, but for this example we instead make use of mplot::compoundray::readEye
     if (mplot::compoundray::readEye (ommatidia.get(), eyefile) == nullptr) { std::cout << "Failed to read eye\n"; return -1; }
 
+    sm::range<sm::vec<float>> ommspan = sm::range<sm::vec<float>>::search_initialized();
+    // Use the eye spacing to control the size of the coord arrows
+    for (auto omm : *ommatidia.get()) {
+        // omm is an Ommatidium. Want to know the x, y and z spans
+        ommspan.update (omm.relativePosition);
+    }
+    float ca_len = eye_scaleup * ommspan.span().max() / 3.0f;
+    auto v = mplot::Visual<>(1024, 768, "mplot::compoundray::EyeVisual");
+    v.showCoordArrows (true);
+    v.coordArrowsInScene (true);
+    v.updateCoordLengths ({ ca_len, ca_len, ca_len }, 1.0f);
+
     // Make some dummy data to demo the eye
     sm::vvec<float> ommatidiaData;
     ommatidiaData.linspace (0, 1, ommatidia->size());
@@ -70,7 +83,7 @@ int main (int argc, char** argv)
 
     [[maybe_unused]] auto ep = v.addVisualModel (eyevm);
     // ep->reinitColours();
-    ep->scaleViewMatrix (1000.0f);
+    ep->scaleViewMatrix (eye_scaleup);
 
     v.keepOpen();
 }

mplot/NavMesh.h

@@ -794,11 +794,20 @@ namespace mplot
          *
          * \param model_to_scene The model to scene transformation for the parent of the navmesh
          *
+         * \param search_dist_mult a multiplier on the search distance. The length of vdir in this
+         * function should cross the landscape model. By default it's the vector from the camera
+         * location in the model frame of reference to the middle of the bounding box. If the vector
+         * is too long when finding the surface of a convex hull, such as a model of a rock, it is
+         * possible to mis-identify the back side of the model. However, for finding a location on a
+         * large, flat, one-sided landscape, we want to make vdir long. search_dist_mult is applied
+         * to vdir.
+         *
          * \return tuple containing: the hit point in scene coordinates; the triangle normal of the
          * triangle we hit; and the indices of the triangle we hit.
          */
         std::tuple<sm::vec<float>, sm::vec<float>, std::array<uint32_t, 4>>
-        find_triangle_hit (const sm::mat44<float>& camspace, const sm::mat44<float>& model_to_scene)
+        find_triangle_hit (const sm::mat44<float>& camspace, const sm::mat44<float>& model_to_scene,
+                           const float search_dist_mult = 1.0f)
         {
             sm::mat44<float> scene_to_model = model_to_scene.inverse();
             // use camera location in gltf to start from, then find model surface.
@@ -807,15 +816,16 @@ namespace mplot
             this->tn0 = {};
             sm::vec<float> hit = {};
             sm::vec<float> vdir = this->bb.mid() - camloc_mf;
-            std::tie (hit, this->ti0, this->tn0) = this->find_triangle_crossing (camloc_mf , vdir);
+            vdir *= search_dist_mult;
+            std::tie (hit, this->ti0, this->tn0) = this->find_triangle_crossing (camloc_mf, vdir);
 
             if (this->ti0[0] == std::numeric_limits<uint32_t>::max()) { std::cout << __func__ << ": No hit\n"; }
 
             sm::vec<float> hp_scene = (model_to_scene * hit).less_one_dim();
 
-            constexpr bool debug = false;
+            constexpr bool debug = true;
             if constexpr (debug) {
-                std::cout << "found hit at " << hit << " (model); " << hp_scene << " (scene)\n";
+                std::cout << "found hit at " << hit << " (model); " << hp_scene << " (scene) in direction " << vdir << "\n";
                 // Check we'll get a hit when we compute_mesh_movement:
                 sm::vec<sm::vec<float>, 3> tv_mf = this->triangle_vertices (this->ti0);
                 std::cout << "tn0: " << this->tn0 << ", length " << this->tn0.length() << std::endl;