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// Copyright 2018 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 "ui/aura_extra/window_occlusion_impl_win.h"
#include "base/win/scoped_gdi_object.h"
#include "ui/aura/window_tree_host.h"
#include "ui/gfx/geometry/rect.h"
namespace aura_extra {
namespace {
// Determines the occlusion status of each aura::Window in |windows_of_interest|
// passed to the constructor. Evaluates a window by subtracting its bounds from
// every window beneath it in the z-order.
class WindowEvaluatorImpl : public WindowEvaluator {
// |windows_of_interest| are the aura::WindowTreeHost's whose occlusion
// status are being calculated. |bounds_delegate| is used to obtain the bounds
// in pixels of each root aura::Window in |windows_of_interest|.
const std::vector<aura::WindowTreeHost*>& windows_of_interest,
std::unique_ptr<WindowBoundsDelegate> bounds_delegate);
// WindowEvaluator.
bool EvaluateWindow(bool is_relevant,
const gfx::Rect& window_rect_in_pixels,
HWND hwnd) override;
// Returns whether there was at least one visible root aura::Window passed to
// ComputeNativeWindowOcclusionStatus().
bool HasAtLeastOneVisibleWindow() const {
return !unoccluded_regions_.empty();
// Called once the occlusion computation is done. Returns |occlusion_states_|
base::flat_map<aura::WindowTreeHost*, aura::Window::OcclusionState>
using WindowRegionPair = std::pair<aura::WindowTreeHost*, SkRegion>;
// Stores intermediate values for the unoccluded regions of an aura::Window in
// pixels. Once an aura::Window::OcclusionState is determined for a root
// aura::Window, that aura::Window is removed from |unoccluded_regions_| and
// added to |occlusion_states_| with the computed
// aura::Window::OcclusionState.
std::vector<WindowRegionPair> unoccluded_regions_;
// Stores the final aura::Window::OcclusionState for each root
// aura::WindowTreeHost that is passed to
// ComputeNativeWindowOcclusionStatus().
base::flat_map<aura::WindowTreeHost*, aura::Window::OcclusionState>
const std::vector<aura::WindowTreeHost*>& windows_of_interest,
std::unique_ptr<WindowBoundsDelegate> bounds_delegate) {
for (aura::WindowTreeHost* window : windows_of_interest) {
// If the window isn't visible at this time, it is
// aura::Window::OcclusionState::HIDDEN.
if (!window->window()->IsVisible() ||
IsIconic(window->GetAcceleratedWidget())) {
occlusion_states_[window] = aura::Window::OcclusionState::HIDDEN;
gfx::Rect window_rect_in_pixels =
SkRegion window_region(SkIRect::MakeXYWH(
window_rect_in_pixels.x(), window_rect_in_pixels.y(),
window_rect_in_pixels.width(), window_rect_in_pixels.height()));
unoccluded_regions_.emplace_back(window, window_region);
WindowEvaluatorImpl::~WindowEvaluatorImpl() = default;
bool WindowEvaluatorImpl::EvaluateWindow(bool is_relevant,
const gfx::Rect& window_rect_in_pixels,
HWND hwnd) {
// Loop through |unoccluded_regions_| and determine how |hwnd| affects each
// root window with respect to occlusion.
for (WindowRegionPair& root_window_pair : unoccluded_regions_) {
HWND window_hwnd = root_window_pair.first->GetAcceleratedWidget();
// The EnumWindows callbacks have reached this window in the Z-order
// (EnumWindows goes from front to back). This window must be visible
// because we did not discover that it was completely occluded earlier.
if (hwnd == window_hwnd) {
occlusion_states_[root_window_pair.first] =
// Set the unoccluded region for this window to empty as a signal that the
// occlusion computation is complete.
// |hwnd| is not taken into account for occlusion computations, move on.
if (!is_relevant)
// Current occlusion state for this window cannot be determined yet. The
// EnumWindows callbacks are currently above this window in the Z-order.
// Subtract the other windows bounding rectangle from this window's
// unoccluded region if the two regions intersect.
SkRegion window_region(SkIRect::MakeXYWH(
window_rect_in_pixels.x(), window_rect_in_pixels.y(),
window_rect_in_pixels.width(), window_rect_in_pixels.height()));
if (root_window_pair.second.intersects(window_region)) {
root_window_pair.second.op(window_region, SkRegion::kDifference_Op);
if (root_window_pair.second.isEmpty()) {
occlusion_states_[root_window_pair.first] =
// Occlusion computation is done for windows with an empty region in
// |unoccluded_regions_|. If the window is visible, the region is set to empty
// explicitly. If it is occluded, the region is implicitly empty.
base::EraseIf(unoccluded_regions_, [](const WindowRegionPair& element) {
return element.second.isEmpty();
// If |unoccluded_regions_| is empty, the occlusion calculation is complete.
// So, we return false to signal to EnumWindows to stop enumerating.
// Otherwise, we want EnumWindows to continue, and return true.
return !unoccluded_regions_.empty();
base::flat_map<aura::WindowTreeHost*, aura::Window::OcclusionState>
WindowEvaluatorImpl::TakeResult() {
return std::move(occlusion_states_);
} // namespace
WindowsDesktopWindowIterator::WindowsDesktopWindowIterator() = default;
void WindowsDesktopWindowIterator::Iterate(WindowEvaluator* evaluator) {
evaluator_ = evaluator;
EnumWindows(&EnumWindowsOcclusionCallback, reinterpret_cast<LPARAM>(this));
BOOL WindowsDesktopWindowIterator::RunEvaluator(HWND hwnd) {
gfx::Rect window_rect;
bool is_relevant = IsWindowVisibleAndFullyOpaque(hwnd, &window_rect);
return evaluator_->EvaluateWindow(is_relevant, window_rect, hwnd);
// static
WindowsDesktopWindowIterator::EnumWindowsOcclusionCallback(HWND hwnd,
LPARAM lParam) {
WindowsDesktopWindowIterator* iterator =
return iterator->RunEvaluator(hwnd);
base::flat_map<aura::WindowTreeHost*, aura::Window::OcclusionState>
const std::vector<aura::WindowTreeHost*>& windows,
std::unique_ptr<NativeWindowIterator> iterator,
std::unique_ptr<WindowBoundsDelegate> bounds_delegate) {
// Time to execute this method, according to 28 days of Stable data
// ending on June 15, 2020:
// 50th percentile: 156 us
// 75th percentile: 273 us
// 95th percentile: 647 us
// 99th percentile: 1939 us
// 99.5th percentile: 5592 us
WindowEvaluatorImpl window_evaluator(windows, std::move(bounds_delegate));
// Only compute occlusion if there was at least one window that is visible.
if (window_evaluator.HasAtLeastOneVisibleWindow())
return window_evaluator.TakeResult();
bool IsWindowVisibleAndFullyOpaque(HWND hwnd, gfx::Rect* rect_in_pixels) {
// Filter out invalid hwnds.
if (!IsWindow(hwnd))
return false;
// Filter out windows that are not “visible”.
if (!IsWindowVisible(hwnd))
return false;
// Filter out minimized windows.
if (IsIconic(hwnd))
return false;
LONG ex_styles = GetWindowLong(hwnd, GWL_EXSTYLE);
// Filter out “transparent” windows, windows where the mouse clicks fall
// through them.
if (ex_styles & WS_EX_TRANSPARENT)
return false;
// Filter out “tool windows”, which are floating windows that do not appear on
// the taskbar or ALT-TAB. Floating windows can have larger window rectangles
// than what is visible to the user, so by filtering them out we will avoid
// incorrectly marking native windows as occluded.
if (ex_styles & WS_EX_TOOLWINDOW)
return false;
// Filter out layered windows.
if (ex_styles & WS_EX_LAYERED)
return false;
// Filter out windows that do not have a simple rectangular region.
base::win::ScopedRegion region(CreateRectRgn(0, 0, 0, 0));
if (GetWindowRgn(hwnd, region.get()) == COMPLEXREGION)
return false;
RECT window_rect;
// Filter out windows that take up zero area. The call to GetWindowRect is one
// of the most expensive parts of this function, so it is last.
if (!GetWindowRect(hwnd, &window_rect))
return false;
if (IsRectEmpty(&window_rect))
return false;
window_rect.right, window_rect.bottom);
return true;
} // namespace aura_extra