Splitting of layers for correct intersections

cc/quads/draw_polygon.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/quads/draw_polygon.h"
 
 #include <vector>
 
 #include "cc/output/bsp_compare_result.h"
 #include "cc/quads/draw_quad.h"
 
 namespace {
 // This allows for some imperfection in the normal comparison when checking if
 // two pieces of geometry are coplanar.
 static const float coplanar_dot_epsilon = 0.01f;
 // This threshold controls how "thick" a plane is. If a point's distance is
 // <= |compare_threshold|, then it is considered on the plane. Only when this
 // boundary is crossed do we consider doing splitting.
 static const float compare_threshold = 1.0f;
 // |split_threshold| is lower in this case because we want the points created
 // during splitting to be well within the range of |compare_threshold| for
 // comparison purposes. The splitting operation will produce intersection points
 // that fit within a tighter distance to the splitting plane as a result of this
 // value. By using a value >= |compare_threshold| we run the risk of creating
 // points that SHOULD be intersecting the "thick plane", but actually fail to
 // test positively for it because |split_threshold| allowed them to be outside
 // this range.
-static const float split_threshold = 0.5f;
+static const float split_threshold = compare_threshold / 2.0f;
 }  // namespace
 
 namespace cc {
 
-gfx::Vector3dF DrawPolygon::default_normal = gfx::Vector3dF(0.0f, 0.0f, -1.0f);
+gfx::Vector3dF DrawPolygon::default_normal = gfx::Vector3dF(0.0f, 0.0f, 1.0f);
 
 DrawPolygon::DrawPolygon() {
 }
 
-DrawPolygon::DrawPolygon(DrawQuad* original,
+DrawPolygon::DrawPolygon(const DrawQuad* original,
                          const std::vector<gfx::Point3F>& in_points,
                          const gfx::Vector3dF& normal,
                          int draw_order_index)
-    : order_index_(draw_order_index), original_ref_(original) {
+    : order_index_(draw_order_index), original_ref_(original), is_split_(true) {
   for (size_t i = 0; i < in_points.size(); i++) {
     points_.push_back(in_points[i]);
   }
   normal_ = normal;
 }
 
 // This takes the original DrawQuad that this polygon should be based on,
 // a visible content rect to make the 4 corner points from, and a transformation
 // to move it and its normal into screen space.
-DrawPolygon::DrawPolygon(DrawQuad* original_ref,
+DrawPolygon::DrawPolygon(const DrawQuad* original_ref,
                          const gfx::RectF& visible_content_rect,
                          const gfx::Transform& transform,
                          int draw_order_index)
-    : order_index_(draw_order_index), original_ref_(original_ref) {
-  normal_ = default_normal;
+    : normal_(default_normal),
+      order_index_(draw_order_index),
+      original_ref_(original_ref),
+      is_split_(false) {
   gfx::Point3F points[8];
   int num_vertices_in_clipped_quad;
   gfx::QuadF send_quad(visible_content_rect);
 
   // Doing this mapping here is very important, since we can't just transform
   // the points without clipping and not run into strange geometry issues when
   // crossing w = 0. At this point, in the constructor, we know that we're
   // working with a quad, so we can reuse the MathUtil::MapClippedQuad3d
   // function instead of writing a generic polygon version of it.
   MathUtil::MapClippedQuad3d(
@@ skipping 22 matching lines @@
 float DrawPolygon::SignedPointDistance(const gfx::Point3F& point) const {
   return gfx::DotProduct(point - points_[0], normal_);
 }
 
 // Checks whether or not shape a lies on the front or back side of b, or
 // whether they should be considered coplanar. If on the back side, we
 // say ABeforeB because it should be drawn in that order.
 // Assumes that layers are split and there are no intersecting planes.
 BspCompareResult DrawPolygon::SideCompare(const DrawPolygon& a,
                                           const DrawPolygon& b) {
+  // Let's make sure that both of these are normalized.
+  DCHECK_GE(0.001f, std::abs(a.normal_.LengthSquared() - 1.0f));

[enne (OOO), 2015/02/04 21:24:00]

Make a constant for this too?

[awoloszyn, 2015/02/12 16:48:52]

Done.

+  DCHECK_GE(0.001f, std::abs(b.normal_.LengthSquared() - 1.0f));
   // Right away let's check if they're coplanar
   double dot = gfx::DotProduct(a.normal_, b.normal_);
   float sign = 0.0f;
   bool normal_match = false;
   // This check assumes that the normals are normalized.
   if (std::abs(dot) >= 1.0f - coplanar_dot_epsilon) {
     normal_match = true;
     // The normals are matching enough that we only have to test one point.
-    sign = gfx::DotProduct(a.points_[0] - b.points_[0], b.normal_);
+    sign = b.SignedPointDistance(a.points_[0]);
     // Is it on either side of the splitter?
     if (sign < -compare_threshold) {
       return BSP_BACK;
     }
 
     if (sign > compare_threshold) {
       return BSP_FRONT;
     }
 
     // No it wasn't, so the sign of the dot product of the normals
@@ skipping 42 matching lines @@
                                gfx::Point3F* intersection,
                                float distance_threshold) {
   gfx::Vector3dF start_to_origin_vector = plane_origin - line_start;
   gfx::Vector3dF end_to_origin_vector = plane_origin - line_end;
 
   double start_distance = gfx::DotProduct(start_to_origin_vector, plane_normal);
   double end_distance = gfx::DotProduct(end_to_origin_vector, plane_normal);
 
   // The case where one vertex lies on the thick-plane and the other
   // is outside of it.
-  if (std::abs(start_distance) < distance_threshold &&
+  if (std::abs(start_distance) <= distance_threshold &&
       std::abs(end_distance) > distance_threshold) {
     intersection->SetPoint(line_start.x(), line_start.y(), line_start.z());
     return true;
   }
 
   // This is the case where we clearly cross the thick-plane.
   if ((start_distance > distance_threshold &&
        end_distance < -distance_threshold) ||
       (start_distance < -distance_threshold &&
        end_distance > distance_threshold)) {
@@ skipping 81 matching lines @@
                            splitter.normal_,
                            &intersections[current_intersection],
                            split_threshold)) {
       vertex_before[current_intersection] = current_vertex % points_size;
       current_intersection++;
       // We found both intersection points so we're done already.
       if (current_intersection == 2) {
         break;
       }
     }
-    if (current_vertex++ > points_size) {
+    if (current_vertex++ > (points_size + 1)) {

[enne (OOO), 2015/02/04 21:24:00]

Can you explain this? Maybe also put the increment on a separate line?

[awoloszyn, 2015/02/12 16:48:52]

I think this is actually un-needed. I had some really good reason for it a few
months ago, I will remove and make sure it is actually not needed, because I
cannot see any reason at the moment.

       break;
     }
   }
   DCHECK_EQ(current_intersection, static_cast<size_t>(2));
 
   // Since we found both the intersection points, we can begin building the
   // vertex set for both our new polygons.
   size_t start1 = (vertex_before[0] + 1) % points_size;
   size_t start2 = (vertex_before[1] + 1) % points_size;
   size_t points_remaining = points_size;
 
   // First polygon.
   out_points[0].push_back(intersections[0]);
+  DCHECK_GE(vertex_before[1], start1);
   for (size_t i = start1; i <= vertex_before[1]; i++) {
     out_points[0].push_back(points_[i]);
     --points_remaining;
   }
   out_points[0].push_back(intersections[1]);
 
   // Second polygon.
   out_points[1].push_back(intersections[1]);
   size_t index = start2;
   for (size_t i = 0; i < points_remaining; i++) {
     out_points[1].push_back(points_[index % points_size]);
     ++index;
   }
   out_points[1].push_back(intersections[0]);
 
   // Give both polygons the original splitting polygon's ID, so that they'll
   // still be sorted properly in co-planar instances.
   scoped_ptr<DrawPolygon> poly1(
       new DrawPolygon(original_ref_, out_points[0], normal_, order_index_));
   scoped_ptr<DrawPolygon> poly2(
       new DrawPolygon(original_ref_, out_points[1], normal_, order_index_));
 
+  DCHECK_GE(poly1->points().size(), 3u);
+  DCHECK_GE(poly2->points().size(), 3u);
+
   if (SideCompare(*poly1, splitter) == BSP_FRONT) {
     *front = poly1.Pass();
     *back = poly2.Pass();
   } else {
     *front = poly2.Pass();
     *back = poly1.Pass();
   }
   return true;
 }
 
@@ skipping 24 matching lines @@
     quads->push_back(
         gfx::QuadF(first,
                    gfx::PointF(points_[offset].x(), points_[offset].y()),
                    gfx::PointF(points_[op1].x(), points_[op1].y()),
                    gfx::PointF(points_[op2].x(), points_[op2].y())));
     offset = op2;
   }
 }
 
 }  // namespace cc