Give extra weight to "edge" triangles when splitting

"Edge" triangles are triangles where one of the edges of the triangle
makes up an edge off the mesh. For example, the triangle E below is an
edge triangle due to the top edge.

This helps prevent jagged "edges" on the tops of mountains, etc. It also
helps round out the edges of the globe  when viewed from far away.

  ________________
  \    ______    /
   \  /\ E  /\  /
    \/__\  /__\/
         \/

diff --git a/src/roam.c b/src/roam.c
index 21b1393c6c902b0202d045ffed0821826840934c..0f4995e0b56593d7bf3dc03f4d65015afb847e8e 100644 (file)
--- a/src/roam.c
+++ b/src/roam.c
@@ -319,7 +319,6 @@ static void roam_triangle_sync_neighbors(RoamTriangle *neigh, RoamTriangle *old,
        if      (neigh->t.l == old) neigh->t.l = new;
        else if (neigh->t.b == old) neigh->t.b = new;
        else if (neigh->t.r == old) neigh->t.r = new;
-       else g_assert_not_reached();
 }
 
 static gboolean roam_triangle_visible(RoamTriangle *triangle, RoamSphere *sphere)
@@ -338,6 +337,20 @@ static gboolean roam_triangle_visible(RoamTriangle *triangle, RoamSphere *sphere
                 l->pz < 1 && m->pz < 1 && r->pz < 1;
 }
 
+static gboolean roam_triangle_backface(RoamTriangle *triangle, RoamSphere *sphere)
+{
+       RoamPoint *l = triangle->p.l;
+       RoamPoint *m = triangle->p.m;
+       RoamPoint *r = triangle->p.r;
+       roam_point_update_projection(l, sphere->view);
+       roam_point_update_projection(m, sphere->view);
+       roam_point_update_projection(r, sphere->view);
+       double size = -( l->px * (m->py - r->py) +
+                        m->px * (r->py - l->py) +
+                        r->px * (l->py - m->py) ) / 2.0;
+       return size < 0;
+}
+
 /**
  * roam_triangle_update_errors:
  * @triangle: the triangle
@@ -375,6 +388,12 @@ void roam_triangle_update_errors(RoamTriangle *triangle, RoamSphere *sphere)
 
                /* Size < 0 == backface */
                triangle->error *= size;
+
+               /* Give some preference to "edge" faces */
+               if (roam_triangle_backface(triangle->t.l, sphere) ||
+                   roam_triangle_backface(triangle->t.b, sphere) ||
+                   roam_triangle_backface(triangle->t.r, sphere))
+                       triangle->error *= 500;
        }
 }
 
@@ -554,6 +573,11 @@ void roam_diamond_merge(RoamDiamond *diamond, RoamSphere *sphere)
        b->kids[0] = b->kids[1] = NULL;
 
        /* Add original triangles */
+       roam_triangle_sync_neighbors(s->t.l, sl, s);
+       roam_triangle_sync_neighbors(s->t.r, sr, s);
+       roam_triangle_sync_neighbors(b->t.l, bl, b);
+       roam_triangle_sync_neighbors(b->t.r, br, b);
+
        roam_triangle_add(s, sl->t.b, b, sr->t.b, sphere);
        roam_triangle_add(b, bl->t.b, s, br->t.b, sphere);