Allow the camera to follow the ball

But when the ground is not textured, this looks just as if the ball was
not moving… :(

main_bounce.cpp

@@ -52,6 +52,7 @@ int main(int argc, char** argv) {
         ground_mesh.get_mesh()->set_color(Color(0.13, 0.82, 0.21));
         render.add_mesh(ground_mesh.get_mesh());
     }
+    //render.follow_implicit_position(ball.get_surface());
 
     render.set_idle_func(periodic_update);
     render.add_kb_handler(periodic_kb_handler);

render/GlutRender.cpp

@@ -12,7 +12,7 @@ GlutRender& GlutRender::get_instance() {
     return instance;
 }
 
-GlutRender::GlutRender() {
+GlutRender::GlutRender() : followed_implicit(nullptr) {
     std::default_random_engine rand_engine(time(NULL));
     std::uniform_real_distribution<double> distribution;
     rand_color = std::bind(distribution, rand_engine);
@@ -97,6 +97,10 @@ void GlutRender::add_kb_handler(GlutRender::kb_handler_t handler) {
     kb_handlers.push_back(handler);
 }
 
+void GlutRender::follow_implicit_position(const ImplicitSurface* surf) {
+    followed_implicit = surf;
+}
+
 void GlutRender::reshape(int wid, int hei) {
     if (hei == 0)
         hei = 1;
@@ -187,10 +191,19 @@ void GlutRender::display() {
 
     // Camera position and orientation
     glLoadIdentity();
-    //glTranslatef(1., 2., -10.);
-    gluLookAt(0, 2.5, -10,
-            0, 2.5, 0,
-            0, 1, 0);
+
+    Point look_from(0, 2.5, -10);
+    if(followed_implicit != nullptr) {
+        const Point& look_at = followed_implicit->getCenter();
+        gluLookAt(look_from.x, look_from.y, look_from.z,
+                look_at.x, look_from.y, look_at.z,
+                0, 1, 0);
+    }
+    else {
+        gluLookAt(look_from.x, look_from.y, look_from.z,
+                0, 2.5, 0,
+                0, 1, 0);
+    }
 
     for(Mesh* mesh: meshes) {
         display_mesh(*mesh);

render/GlutRender.hpp

@@ -30,6 +30,8 @@ class GlutRender {
 
         void add_kb_handler(kb_handler_t handler);
 
+        void follow_implicit_position(const ImplicitSurface* surf);
+
     private:
         struct SurfaceDetails {
             SurfaceDetails(ImplicitSurface* surf, const Cuboid& box,
@@ -68,4 +70,6 @@ class GlutRender {
         std::set<SurfaceDetails> surfaces;
 
         std::vector<kb_handler_t> kb_handlers;
+
+        const ImplicitSurface* followed_implicit;
 };