desks: Add edge padding for continuous gesture swipe.

Increase the animation layer on each side by a ratio of the root window
width. When swiping, users can see this padding if they swipe towards a
direction with no more desks (i.e. swipe right at desk 0). Clamps the
translation such that the entire animation layer is always visible.

Tested that the edge padding does not affect non continuous gestures.
Though not seen, the edge padding is there for simplification. Can be
easily modified if desired in the future.

Test: manual
Bug: 1111445
Change-Id: I3b204d8ef1e1648b421310e1aa714346a94959aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417491
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809423}

ash/wm/desks/root_window_desk_switch_animator.cc

@@ -11,6 +11,7 @@
 #include "ash/wm/desks/desks_util.h"
 #include "base/auto_reset.h"
 #include "base/logging.h"
+#include "base/numerics/ranges.h"
 #include "base/strings/string_number_conversions.h"
 #include "components/viz/common/frame_sinks/copy_output_request.h"
 #include "components/viz/common/frame_sinks/copy_output_result.h"
@@ -47,7 +48,13 @@ constexpr base::TimeDelta kAnimationDuration =
 
 // In touchpad units, a touchpad swipe of this length will correspond to a full
 // desk change.
-constexpr int kTouchpadSwipeLengthForDeskChange = 300;
+constexpr int kTouchpadSwipeLengthForDeskChange = 100;
+
+// The animation layer has extra padding at its two edges. The width in dips is
+// a ratio of the root window width. This padding is to notify users there are
+// no more desks on that side by showing a black region as we swipe
+// continuously.
+constexpr float kEdgePaddingRatio = 0.15f;
 
 // The amount, by which the detached old layers of the removed desk's windows,
 // is translated vertically during the for-remove desk switch animation.
@@ -134,6 +141,8 @@ RootWindowDeskSwitchAnimator::RootWindowDeskSwitchAnimator(
       delegate_(delegate),
       animation_layer_owner_(CreateAnimationLayerOwner(root)),
       x_translation_offset_(root->layer()->size().width() + kDesksSpacing),
+      edge_padding_width_dp_(
+          std::round(root_window_->bounds().width() * kEdgePaddingRatio)),
       for_remove_(for_remove) {
   DCHECK(root_window_);
   DCHECK_NE(starting_desk_index_, ending_desk_index_);
@@ -248,12 +257,24 @@ bool RootWindowDeskSwitchAnimator::UpdateSwipeAnimation(float scroll_delta_x) {
     return false;
 
   const float translation_delta_x =
-      TouchpadToXTranslation(scroll_delta_x, x_translation_offset_) * 5.f;
+      TouchpadToXTranslation(scroll_delta_x, x_translation_offset_);
+
+  // The visible bounds to the user are the root window bounds which always have
+  // origin of 0,0. Therefore the rightmost edge of the visible bounds will be
+  // the width.
+  const int visible_bounds_width =
+      root_window_->GetBoundsInRootWindow().width();
 
-  // Append the new offset to the current transform.
+  // Append the new offset to the current transform. Clamp the new transform so
+  // that we do not swipe past the edges.
   auto* animation_layer = animation_layer_owner_->root();
-  gfx::Transform transform = animation_layer->transform();
-  transform.Translate(translation_delta_x, 0.f);
+  float translation_x =
+      animation_layer->transform().To2dTranslation().x() + translation_delta_x;
+  translation_x = base::ClampToRange(
+      translation_x,
+      float{-animation_layer->bounds().width() + visible_bounds_width}, 0.f);
+  gfx::Transform transform;
+  transform.Translate(translation_x, 0.f);
   base::AutoReset<bool> auto_reset(&setting_new_transform_, true);
   animation_layer->SetTransform(transform);
 
@@ -278,11 +299,6 @@ bool RootWindowDeskSwitchAnimator::UpdateSwipeAnimation(float scroll_delta_x) {
   gfx::RectF transformed_animation_layer_bounds(animation_layer->bounds());
   transform.TransformRect(&transformed_animation_layer_bounds);
 
-  // The visible bounds to the user are the root window bounds which always have
-  // origin of 0,0. Therefore the rightmost edge of the visible bounds will be
-  // the width.
-  const int visible_bounds_width =
-      root_window_->GetBoundsInRootWindow().width();
   const bool moving_left = scroll_delta_x < 0.f;
   const bool going_out_of_bounds =
       moving_left
@@ -431,15 +447,18 @@ void RootWindowDeskSwitchAnimator::OnScreenshotLayerCreated() {
     if (!layer)
       continue;
 
-    const int x = num_screenshots * x_translation_offset_;
+    const int x =
+        num_screenshots * x_translation_offset_ + edge_padding_width_dp_;
     layer->SetBounds(gfx::Rect(gfx::Point(x, 0), root_window_size));
     ++num_screenshots;
   }
 
-  // The animation layer is sized to contain all the screenshot layers plus
-  // |kDesksSpacing| between any two adjacent screenshot layers.
+  // The animation layer is sized to contain all the screenshot layers,
+  // |kDesksSpacing| between any two adjacent screenshot layers, and
+  // |edge_padding_width_dp_| on each side.
   const gfx::Rect animation_layer_bounds(
-      num_screenshots * x_translation_offset_ - kDesksSpacing,
+      num_screenshots * x_translation_offset_ - kDesksSpacing +
+          2 * edge_padding_width_dp_,
       root_window_size.height());
   auto* animation_layer = animation_layer_owner_->root();
   animation_layer->SetBounds(animation_layer_bounds);

ash/wm/desks/root_window_desk_switch_animator.h

@@ -299,6 +299,9 @@ class RootWindowDeskSwitchAnimator : public ui::ImplicitAnimationObserver {
   // of the desk indices.
   const int x_translation_offset_;
 
+  // The amount of padding in dips on the edges of the animation layer.
+  const int edge_padding_width_dp_;
+
   // Number of retires for taking the starting and ending screenshots, if we
   // get an empty result.
   int starting_desk_screenshot_retries_ = 0;