desks: Add shadow to mini views.

Test: manual
Bug: 988521

Change-Id: Iee9cc88044ecdef9b42645cadce9dd2037918dec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1771672
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692105}

ash/wm/desks/desk_preview_view.cc

@@ -12,7 +12,10 @@
 #include "base/containers/flat_map.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_tree_owner.h"
+#include "ui/compositor/paint_recorder.h"
+#include "ui/gfx/canvas.h"
 #include "ui/gfx/geometry/rounded_corners_f.h"
+#include "ui/gfx/skia_paint_util.h"
 
 namespace ash {
 
@@ -26,7 +29,10 @@ constexpr int kDeskPreviewHeight = 64;
 constexpr int kBorderSize = 2;
 
 // The rounded corner radii, also in dips.
-constexpr gfx::RoundedCornersF kCornerRadii(4);
+constexpr int kCornerRadius = 4;
+constexpr gfx::RoundedCornersF kCornerRadii(kCornerRadius);
+
+constexpr int kShadowElevation = 4;
 
 // Holds data about the original desk's layers to determine what we should do
 // when we attempt to mirror those layers.
@@ -136,6 +142,56 @@ void GetLayersData(aura::Window* window,
 
 }  // namespace
 
+// -----------------------------------------------------------------------------
+// DeskPreviewView::ShadowRenderer
+
+// Layer delegate which handles drawing a shadow around DeskPreviewView.
+class DeskPreviewView::ShadowRenderer : public ui::LayerDelegate {
+ public:
+  ShadowRenderer()
+      : shadow_values_(gfx::ShadowValue::MakeMdShadowValues(kShadowElevation)) {
+  }
+
+  ~ShadowRenderer() override = default;
+
+  gfx::Rect GetPaintedBounds() const {
+    gfx::Rect total_rect(bounds_);
+    total_rect.Inset(gfx::ShadowValue::GetMargin(shadow_values_));
+    return total_rect;
+  }
+
+  void set_bounds(const gfx::Rect& bounds) { bounds_ = bounds; }
+
+ private:
+  // ui::LayerDelegate:
+  void OnPaintLayer(const ui::PaintContext& context) override {
+    ui::PaintRecorder recorder(context, bounds_.size());
+
+    cc::PaintFlags shadow_flags;
+    shadow_flags.setAntiAlias(true);
+    shadow_flags.setLooper(gfx::CreateShadowDrawLooper(shadow_values_));
+
+    const gfx::Rect rrect_bounds =
+        bounds_ - GetPaintedBounds().OffsetFromOrigin();
+    const auto r_rect = SkRRect::MakeRectXY(gfx::RectToSkRect(rrect_bounds),
+                                            kCornerRadius, kCornerRadius);
+    recorder.canvas()->sk_canvas()->clipRRect(r_rect, SkClipOp::kDifference,
+                                              /*do_anti_alias=*/true);
+    recorder.canvas()->sk_canvas()->drawRRect(r_rect, shadow_flags);
+  }
+
+  void OnDeviceScaleFactorChanged(float old_device_scale_factor,
+                                  float new_device_scale_factor) override {}
+
+  gfx::Rect bounds_;
+  const gfx::ShadowValues shadow_values_;
+
+  DISALLOW_COPY_AND_ASSIGN(ShadowRenderer);
+};
+
+// -----------------------------------------------------------------------------
+// DeskPreviewView
+
 DeskPreviewView::DeskPreviewView(DeskMiniView* mini_view)
     : mini_view_(mini_view),
       background_view_(new views::View),
@@ -143,11 +199,16 @@ DeskPreviewView::DeskPreviewView(DeskMiniView* mini_view)
       desk_mirrored_contents_view_(new views::View),
       force_occlusion_tracker_visible_(
           std::make_unique<aura::WindowOcclusionTracker::ScopedForceVisible>(
-              mini_view->GetDeskContainer())) {
+              mini_view->GetDeskContainer())),
+      shadow_delegate_(std::make_unique<ShadowRenderer>()) {
   DCHECK(mini_view_);
 
   SetPaintToLayer(ui::LAYER_NOT_DRAWN);
-  layer()->SetMasksToBounds(true);
+  layer()->SetMasksToBounds(false);
+
+  shadow_layer_.SetFillsBoundsOpaquely(false);
+  layer()->Add(&shadow_layer_);
+  shadow_layer_.set_delegate(shadow_delegate_.get());
 
   background_view_->SetPaintToLayer(ui::LAYER_SOLID_COLOR);
   auto* background_layer = background_view_->layer();
@@ -218,6 +279,8 @@ const char* DeskPreviewView::GetClassName() const {
 
 void DeskPreviewView::Layout() {
   gfx::Rect bounds = GetLocalBounds();
+  shadow_delegate_->set_bounds(bounds);
+  shadow_layer_.SetBounds(shadow_delegate_->GetPaintedBounds());
   background_view_->SetBoundsRect(bounds);
   bounds.Inset(kBorderSize, kBorderSize);
   wallpaper_preview_->SetBoundsRect(bounds);

ash/wm/desks/desk_preview_view.h

@@ -79,6 +79,8 @@ class DeskPreviewView : public views::View {
   void Layout() override;
 
  private:
+  class ShadowRenderer;
+
   DeskMiniView* const mini_view_;
 
   // A view to paint a background color behind the |wallpaper_preview_| to
@@ -107,6 +109,9 @@ class DeskPreviewView : public views::View {
   std::unique_ptr<aura::WindowOcclusionTracker::ScopedForceVisible>
       force_occlusion_tracker_visible_;
 
+  ui::Layer shadow_layer_;
+  std::unique_ptr<ShadowRenderer> shadow_delegate_;
+
   DISALLOW_COPY_AND_ASSIGN(DeskPreviewView);
 };