g/frustum: simplify aabb intersection test

geom/frustum.hpp

@@ -47,20 +47,17 @@ namespace util::geom {
     intersects (const frustum<T> &f, const aabb<S,T> &b)
     {
         for (const auto &p: f.planes) {
-            const auto n = normal (p);
-            const auto positive = n > 0;
+            // find the distance to the point, if it's positive it's inside
+            // the frustum.
+            const auto d = max (
+                p.coefficients * b.lo.template redim<S+1> (1),
+                p.coefficients * b.hi.template redim<S+1> (1)
+            );
 
-            const auto lo = select (positive, b.lo, b.hi);
-            const auto hi = select (positive, b.hi, b.lo);
-
-            if (dot (n, lo) + p.coefficients[S] > 0)
-                return false; // OUTSIDE
-
-            if (dot (n, hi) + p.coefficients[S] >= 0)
-                return true; //INTERSECT
+            if (sum (d) < 0)
+                return false;
         }
 
-        // INSIDE
         return true;
     }
 };

test/geom/frustum.cpp

@@ -25,6 +25,7 @@ main ()
         { { { -1, -1, -1 }, {  1,  1,  1 } }, true,  "covers origin with unit radius" },
         { { { -9, -9, -9 }, { -8, -8, -8 } }, false, "out of view negative" },
         { { { -1, -1,  2 }, {  1,  1,  3 } }, false, "past far plane" },
+        { { {  0,  0,  0 }, {  0,  0,  0 } }, false, "before near plane" },
     };
 
     for (const auto &t: TESTS) {