Cache bounding boxes.

This results in massive performance improvements for hit testing.
Files with very large amounts of entities (e.g. [1]) inflict
a delay of several seconds between moving the pointer and
highlighting an entity in commit HEAD^^^, whereas in this commit
the delay is barely perceptible.

[1]: http://solvespace.com/forum.pl?action=viewthread&parent=872

src/draw.cpp

@@ -318,6 +318,20 @@ void GraphicsWindow::HitTestMakeSelection(Point2d mp) {
     double d, dmin = 1e12;
     Selection s = {};
 
+    // Did the view projection change? If so, invalidate bounding boxes.
+    if(!offset.EqualsExactly(cached.offset) ||
+           !projRight.EqualsExactly(cached.projRight) ||
+           !projUp.EqualsExactly(cached.projUp) ||
+           EXACT(scale != cached.scale)) {
+        cached.offset = offset;
+        cached.projRight = projRight;
+        cached.projUp = projUp;
+        cached.scale = scale;
+        for(Entity *e = SK.entity.First(); e; e = SK.entity.NextAfter(e)) {
+            e->screenBBoxValid = false;
+        }
+    }
+
     // Always do the entities; we might be dragging something that should
     // be auto-constrained, and we need the hover for that.
     for(i = 0; i < SK.entity.n; i++) {

src/drawentity.cpp

@@ -152,35 +152,38 @@ SEdgeList *Entity::GetOrGenerateEdges() {
     return &edges;
 }
 
-BBox Entity::GetScreenBBox(bool *hasBBox) {
+BBox Entity::GetOrGenerateScreenBBox(bool *hasBBox) {
     SBezierList *sbl = GetOrGenerateBezierCurves();
 
     // We don't bother with bounding boxes for normals, workplanes, etc.
     *hasBBox = (IsPoint() || sbl->l.n > 0);
     if(!*hasBBox) return {};
 
-    BBox result = {};
+    if(screenBBoxValid)
+        return screenBBox;
+
     if(IsPoint()) {
         Vector proj = SS.GW.ProjectPoint3(PointGetNum());
-        result = BBox::From(proj, proj);
+        screenBBox = BBox::From(proj, proj);
     } else if(sbl->l.n > 0) {
         Vector first = SS.GW.ProjectPoint3(sbl->l.elem[0].ctrl[0]);
-        result = BBox::From(first, first);
+        screenBBox = BBox::From(first, first);
         for(int i = 0; i < sbl->l.n; i++) {
             SBezier *sb = &sbl->l.elem[i];
             for(int i = 0; i <= sb->deg; i++) {
-                result.Include(SS.GW.ProjectPoint3(sb->ctrl[i]));
+                screenBBox.Include(SS.GW.ProjectPoint3(sb->ctrl[i]));
             }
         }
     } else oops();
 
     // Enlarge the bounding box to consider selection radius.
-    result.minp.x -= SELECTION_RADIUS;
-    result.minp.y -= SELECTION_RADIUS;
-    result.maxp.x += SELECTION_RADIUS;
-    result.maxp.y += SELECTION_RADIUS;
+    screenBBox.minp.x -= SELECTION_RADIUS;
+    screenBBox.minp.y -= SELECTION_RADIUS;
+    screenBBox.maxp.x += SELECTION_RADIUS;
+    screenBBox.maxp.y += SELECTION_RADIUS;
 
-    return result;
+    screenBBoxValid = true;
+    return screenBBox;
 }
 
 double Entity::GetDistance(Point2d mp) {
@@ -508,7 +511,7 @@ void Entity::DrawOrGetDistance(void) {
     // whether the pointer is inside its bounding box first.
     if(!dogd.drawing) {
         bool hasBBox;
-        BBox box = GetScreenBBox(&hasBBox);
+        BBox box = GetOrGenerateScreenBBox(&hasBBox);
         if(hasBBox && !box.Contains(dogd.mp))
             return;
     }

src/sketch.h

@@ -455,7 +455,8 @@ public:
     // POD members with indeterminate value.
     Entity() : EntityBase({}), forceHidden(), actPoint(), actNormal(),
         actDistance(), actVisible(), style(), construction(),
-        dogd(), beziers(), edges(), edgesChordTol() {};
+        dogd(), beziers(), edges(), edgesChordTol(), screenBBox(),
+        screenBBoxValid() {};
 
     // An imported entity that was hidden in the source file ends up hidden
     // here too.
@@ -476,6 +477,8 @@ public:
     SBezierList beziers;
     SEdgeList   edges;
     double      edgesChordTol;
+    BBox        screenBBox;
+    bool        screenBBoxValid;
 
     // Routines to draw and hit-test the representation of the entity
     // on-screen.
@@ -509,7 +512,7 @@ public:
 
     SBezierList *GetOrGenerateBezierCurves();
     SEdgeList *GetOrGenerateEdges();
-    BBox GetScreenBBox(bool *hasBBox);
+    BBox GetOrGenerateScreenBBox(bool *hasBBox);
 
     void Clear() {
         beziers.l.Clear();

src/ui.h

@@ -487,6 +487,14 @@ public:
         Vector  marqueePoint;
         bool    startedMoving;
     }       orig;
+    // We need to detect when the projection is changed to invalidate
+    // caches for drawn items.
+    struct {
+        Vector  offset;
+        Vector  projRight;
+        Vector  projUp;
+        double  scale;
+    }       cached;
 
     // Most recent mouse position, updated every time the mouse moves.
     Point2d currentMousePosition;