Disable Normal DCHECK

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 <stddef.h>
 
 #include <vector>
 
@@ skipping 25 matching lines @@
 }
 
 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), is_split_(true) {
   for (size_t i = 0; i < in_points.size(); i++) {
     points_.push_back(in_points[i]);
   }
-#if DCHECK_IS_ON()
   normal_ = normal;

[danakj, 2017/03/17 14:14:44]

can this be initialized in the constructor init list (like "normal_(normal)")
above then?

[Peter Mayo, 2017/03/17 16:04:07]

Yes, that makes sense now.  Done.

-  ConstructNormal();
-  DCHECK_LE((normal_ - normal).Length(), normalized_threshold);
-#endif
-  normal_ = normal;
+  // If life was fair, we could recalculate the normal from the given points
+  // and assert it was roughly the same.  This causes unhelpful breaks on
+  // trivial slices of split polygons.  Similarly, when splitting, it is
+  // better to keep the normal that was constructed from the original.
 }
 
 // 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(const DrawQuad* original_ref,
                          const gfx::RectF& visible_layer_rect,
                          const gfx::Transform& transform,
                          int draw_order_index)
     : normal_(0.0f, 0.0f, 1.0f),
@@ skipping 280 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