Optimize bounding box bisection with more early culling

[libs/math.git] / source / geometry / shape.h

diff --git a/source/geometry/shape.h b/source/geometry/shape.h
index 074c11b7289665fa88786aa43b5a4343c06e0741..920e4560454799d7828a50a9601e3ad4ba2295b7 100644 (file)
--- a/source/geometry/shape.h
+++ b/source/geometry/shape.h
@@ -14,6 +14,7 @@ namespace Geometry {
 enum Coverage
 {
        NO_COVERAGE,
+       UNCERTAIN_COVERAGE,
        PARTIAL_COVERAGE,
        FULL_COVERAGE
 };
@@ -40,15 +41,27 @@ public:
 
        virtual Shape *clone() const = 0;
 
+       /** Returns the bounding box of the shape.  The detail parameter controls
+       the tightness of the box.  Higher detail will take more time to compute. */
        virtual BoundingBox<T, D> get_axis_aligned_bounding_box(unsigned detail = 0) const = 0;
 protected:
        BoundingBox<T, D> bisect_axis_aligned_bounding_box(unsigned) const;
+
 public:
+       /** Checks if a point is contained within the shape. */
        virtual bool contains(const LinAl::Vector<T, D> &) const = 0;
+
        bool check_intersection(const Ray<T, D> &) const;
        virtual unsigned get_max_ray_intersections() const = 0;
+
+       /** Determines intersection points between the shape and a ray. */
        virtual unsigned get_intersections(const Ray<T, D> &, SurfacePoint<T, D> *, unsigned) const = 0;
+
+       /** Returns a vector with all of the intersections between the shape and a
+       ray. */
        std::vector<SurfacePoint<T, D> > get_intersections(const Ray<T, D> &) const;
+
+       /** Determines whether the shape covers a bounding box. */
        virtual Coverage get_coverage(const BoundingBox<T, D> &) const = 0;
 };
 
@@ -58,18 +71,23 @@ inline BoundingBox<T, D> Shape<T, D>::bisect_axis_aligned_bounding_box(unsigned
        if(!detail)
                throw std::invalid_argument("Shape::bisect_axis_aligned_bounding_box");
 
+       // Form the root cell from the loosest approximation of a bounding box.
        std::list<CoverageCell> queue;
        queue.push_back(CoverageCell());
        CoverageCell &root = queue.front();
        root.level = 0;
        root.bounding_box = get_axis_aligned_bounding_box();
+       // There's no point bisecting if the bounding box fills the entire space.
        if(root.bounding_box.is_space())
                return root.bounding_box;
 
        root.coverage = get_coverage(root.bounding_box);
+       // If the bounding box is fully covered it's already tight.
        if(root.coverage==FULL_COVERAGE)
                return root.bounding_box;
 
+       /* Initialize bounds to the opposite edges because we don't yet know which
+       part of the bounding box the shape occupies. */
        LinAl::Vector<T, D> tight_min_pt = root.bounding_box.get_maximum_point();
        LinAl::Vector<T, D> tight_max_pt = root.bounding_box.get_minimum_point();
 
@@ -79,8 +97,20 @@ inline BoundingBox<T, D> Shape<T, D>::bisect_axis_aligned_bounding_box(unsigned
 
                const LinAl::Vector<T, D> &min_pt = cell.bounding_box.get_minimum_point();
                const LinAl::Vector<T, D> &max_pt = cell.bounding_box.get_maximum_point();
+
+               // Skip cells that are already fully inside the established bounds.
+               bool internal = true;
+               for(unsigned i=0; (i<D && internal); ++i)
+                       internal = (min_pt[i]>=tight_min_pt[i] && max_pt[i]<=tight_max_pt[i]);
+               if(internal)
+               {
+                       queue.pop_front();
+                       continue;
+               }
+
                LinAl::Vector<T, D> center = (min_pt+max_pt)/T(2);
 
+               // Bisect each dimension.
                for(unsigned i=0; i<(1<<D); ++i)
                {
                        CoverageCell child;
@@ -100,6 +130,8 @@ inline BoundingBox<T, D> Shape<T, D>::bisect_axis_aligned_bounding_box(unsigned
                        child.coverage = get_coverage(child.bounding_box);
                        if(child.coverage==FULL_COVERAGE || (child.level==detail && child.coverage!=NO_COVERAGE))
                        {
+                               /* Immediately merge cells with full coverage.  Also merge cells
+                               at the last level. */
                                for(unsigned j=0; j<D; ++j)
                                {
                                        tight_min_pt[j] = std::min(tight_min_pt[j], child_min_pt[j]);
@@ -107,6 +139,17 @@ inline BoundingBox<T, D> Shape<T, D>::bisect_axis_aligned_bounding_box(unsigned
                                }
                        }
                        else if(child.coverage==PARTIAL_COVERAGE)
+                       {
+                               /* Merge cells with confirmed partial coverage so the cell is
+                               left just outside the bounding box. */
+                               for(unsigned j=0; j<D; ++j)
+                               {
+                                       tight_min_pt[j] = std::min(tight_min_pt[j], child_max_pt[j]);
+                                       tight_max_pt[j] = std::max(tight_max_pt[j], child_min_pt[j]);
+                               }
+                       }
+
+                       if(child.level<detail && child.coverage!=NO_COVERAGE && child.coverage!=FULL_COVERAGE)
                                queue.push_back(child);
                }