Revert of Perform BSP polygon splitting and orientation selection in a single step. (patchset Pissandshittium#4 id:60001 of https://codereview.chromium.org/2043283002/ )

Reason for revert:
Broke Windows 7 cc_unittests: DrawPolygonSplitTest.AngledSplit
https://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%281%29/builds/53692

Original issue's description:
> Perform BSP polygon splitting and orientation selection in a single step.
>
> This eliminates redundant testing of vertices for orientation with
> respect to the splitting polygon. Previously, up to 3 sets of tests
> were made (once to determine whether the polygon was split, then once
> during the split, and then finally to determine the orientation of the
> split polygons.
>
> Merging these steps in order to reuse calculated values also eliminates
> the possibility that different calculations in testing and splitting
> could be inconsistent.
>
> BUG=606984
> CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
>
> Committed: https://crrev.com/89c62c8f69d76471e866f21ee4f1ae5e0c5bca48
> Cr-Commit-Position: refs/heads/master@{#399459}

TBR=enne@chromium.org,tobiasjs@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=606984

Review-Url: https://codereview.chromium.org/2060183003
Cr-Commit-Position: refs/heads/master@{#399472}

Author: fsamuel

cc/output/bsp_tree.cc

@@ -44,24 +44,46 @@ void BspTree::BuildTree(
   // find a splitting plane, then classify polygons as either in front of
   // or behind that splitting plane.
   while (!polygon_list->empty()) {
-    std::unique_ptr<DrawPolygon> polygon;
-    std::unique_ptr<DrawPolygon> new_front;
-    std::unique_ptr<DrawPolygon> new_back;
-    // Time to split this geometry, *it needs to be split by node_data.
-    polygon = PopFront(polygon_list);
-    bool is_coplanar;
-    node->node_data->SplitPolygon(std::move(polygon), &new_front, &new_back,
-                                  &is_coplanar);
-    if (is_coplanar) {
-      if (new_front)
-        node->coplanars_front.push_back(std::move(new_front));
-      if (new_back)
-        node->coplanars_back.push_back(std::move(new_back));
-    } else {
-      if (new_front)
+    // Is this particular polygon in front of or behind our splitting polygon.
+    BspCompareResult comparer_result =
+        GetNodePositionRelative(*polygon_list->front(), *(node->node_data));
+
+    // If it's clearly behind or in front of the splitting plane, we use the
+    // heuristic to decide whether or not we should put it at the back
+    // or front of the list.
+    switch (comparer_result) {
+      case BSP_FRONT:
+        front_list.push_back(PopFront(polygon_list));
+        break;
+      case BSP_BACK:
+        back_list.push_back(PopFront(polygon_list));
+        break;
+      case BSP_SPLIT:
+      {
+        std::unique_ptr<DrawPolygon> polygon;
+        std::unique_ptr<DrawPolygon> new_front;
+        std::unique_ptr<DrawPolygon> new_back;
+        // Time to split this geometry, *it needs to be split by node_data.
+        polygon = PopFront(polygon_list);
+        bool split_result =
+            polygon->Split(*(node->node_data), &new_front, &new_back);
+        DCHECK(split_result);
+        if (!split_result) {
+          break;
+        }
         front_list.push_back(std::move(new_front));
-      if (new_back)
         back_list.push_back(std::move(new_back));
+        break;
+      }
+      case BSP_COPLANAR_FRONT:
+        node->coplanars_front.push_back(PopFront(polygon_list));
+        break;
+      case BSP_COPLANAR_BACK:
+        node->coplanars_back.push_back(PopFront(polygon_list));
+        break;
+      default:
+        NOTREACHED();
+        break;
     }
   }
 
@@ -78,6 +100,11 @@ void BspTree::BuildTree(
   }
 }
 
+BspCompareResult BspTree::GetNodePositionRelative(const DrawPolygon& node_a,
+                                                  const DrawPolygon& node_b) {
+  return DrawPolygon::SideCompare(node_a, node_b);
+}
+
 // The base comparer with 0,0,0 as camera position facing forward
 BspCompareResult BspTree::GetCameraPositionRelative(const DrawPolygon& node) {
   if (node.normal().z() > 0.0f) {

cc/output/bsp_tree.h

@@ -101,6 +101,10 @@ class CC_EXPORT BspTree {
     }
   }
 
+  // Returns whether or not nodeA is on one or the other side of nodeB,
+  // coplanar, or whether it crosses nodeB's plane and needs to be split
+  static BspCompareResult GetNodePositionRelative(const DrawPolygon& node_a,
+                                                  const DrawPolygon& node_b);
   // Returns whether or not our viewer is in front of or behind the plane
   // defined by this polygon/node
   static BspCompareResult GetCameraPositionRelative(const DrawPolygon& node);

cc/output/bsp_tree_unittest.cc

@@ -45,50 +45,24 @@ class BspTreeTest {
     EXPECT_TRUE(VerifySidedness(bsp_tree.root()));
   }
 
-  static BspCompareResult SideCompare(const DrawPolygon& a,
-                                      const DrawPolygon& b) {
-    const float split_threshold = 0.05f;
-    bool pos = false;
-    bool neg = false;
-    for (const auto& pt : a.points()) {
-      float dist = b.SignedPointDistance(pt);
-      neg |= dist < -split_threshold;
-      pos |= dist > split_threshold;
-    }
-    if (pos && neg)
-      return BSP_SPLIT;
-    if (neg)
-      return BSP_BACK;
-    if (pos)
-      return BSP_FRONT;
-    double dot = gfx::DotProduct(a.normal(), b.normal());
-    if ((dot >= 0.0f && a.order_index() >= b.order_index()) ||
-        (dot <= 0.0f && a.order_index() <= b.order_index())) {
-      // The sign of the dot product of the normals along with document order
-      // determine which side it goes on, the vertices are ambiguous.
-      return BSP_COPLANAR_BACK;
-    }
-    return BSP_COPLANAR_FRONT;
-  }
-
   static bool VerifySidedness(const std::unique_ptr<BspNode>& node) {
     // We check if both the front and back child nodes have geometry that is
     // completely on the expected side of the current node.
     bool front_ok = true;
     bool back_ok = true;
     if (node->back_child) {
       // Make sure the back child lies entirely behind this node.
-      BspCompareResult result =
-          SideCompare(*(node->back_child->node_data), *(node->node_data));
+      BspCompareResult result = DrawPolygon::SideCompare(
+          *(node->back_child->node_data), *(node->node_data));
       if (result != BSP_BACK) {
         return false;
       }
       back_ok = VerifySidedness(node->back_child);
     }
     // Make sure the front child lies entirely in front of this node.
     if (node->front_child) {
-      BspCompareResult result =
-          SideCompare(*(node->front_child->node_data), *(node->node_data));
+      BspCompareResult result = DrawPolygon::SideCompare(
+          *(node->front_child->node_data), *(node->node_data));
       if (result != BSP_FRONT) {
         return false;
       }
@@ -100,15 +74,15 @@ class BspTreeTest {
 
     // Now we need to make sure our coplanar geometry is all actually coplanar.
     for (size_t i = 0; i < node->coplanars_front.size(); i++) {
-      BspCompareResult result =
-          SideCompare(*(node->coplanars_front[i]), *(node->node_data));
+      BspCompareResult result = DrawPolygon::SideCompare(
+          *(node->coplanars_front[i]), *(node->node_data));
       if (result != BSP_COPLANAR_FRONT) {
         return false;
       }
     }
     for (size_t i = 0; i < node->coplanars_back.size(); i++) {
-      BspCompareResult result =
-          SideCompare(*(node->coplanars_back[i]), *(node->node_data));
+      BspCompareResult result = DrawPolygon::SideCompare(
+          *(node->coplanars_back[i]), *(node->node_data));
       if (result != BSP_COPLANAR_BACK) {
         return false;
       }