Draw omnibox shadow with a ninebox layer.

cc/layers/nine_patch_layer.h

 // Copyright 2012 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.
 
 #ifndef CC_LAYERS_NINE_PATCH_LAYER_H_
 #define CC_LAYERS_NINE_PATCH_LAYER_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "cc/base/cc_export.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/ui_resource_layer.h"
 #include "cc/resources/ui_resource_client.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace cc {
 
 class CC_EXPORT NinePatchLayer : public UIResourceLayer {
  public:
   static scoped_refptr<NinePatchLayer> Create();
 
   void PushPropertiesTo(LayerImpl* layer) override;
 
   // |border| is the space around the center rectangular region in layer space
   // (known as aperture in image space).  |border.x()| and |border.y()| are the
   // size of the left and top boundary, respectively.
   // |border.width()-border.x()| and |border.height()-border.y()| are the size
   // of the right and bottom boundary, respectively.
+  // TODO(estade): this really ought to be a gfx::Insets and not a gfx::Rect. To

[Evan Stade, 2016/12/01 02:39:02]

does this make sense? This API was a bit of a head scratcher for me and it's
pretty hard to debug when you can't figure out what the rect is supposed to be.

In fact, I'm not sure why we even need SetBorder. It seems like it's redundant
once you know the occlusion and the aperture.

In fact^2, it seems like aperture and layer bounds should be enough. Why do we
even need occlusion? Seems like we should just assume the outer edges of the
ninebox align to the edges of the layer's bounds.

+  // convert from rect to insets, think of x() as left(), y() as top(), width()
+  // - x() as right(), and height() - y() as bottom().
   void SetBorder(const gfx::Rect& border);
 
   // aperture is in the pixel space of the bitmap resource and refers to
   // the center patch of the ninepatch (which is unused in this
   // implementation). We split off eight rects surrounding it and stick them
   // on the edges of the layer. The corners are unscaled, the top and bottom
   // rects are x-stretched to fit, and the left and right rects are
   // y-stretched to fit.
   void SetAperture(const gfx::Rect& aperture);
   void SetFillCenter(bool fill_center);
@@ skipping 20 matching lines @@
   // The occluded region in layer space set by SetLayerOcclusion. It is
   // usually larger than |image_aperture_|.
   gfx::Rect layer_occlusion_;
 
   DISALLOW_COPY_AND_ASSIGN(NinePatchLayer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_NINE_PATCH_LAYER_H_