Use PrintWindow() to implement snapshots on windows 8.1+

ui/snapshot/snapshot_win.cc

+// Copyright 2017 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/snapshot/snapshot_win.h"
+
+#include "base/callback.h"
+#include "base/task_runner.h"
+#include "base/win/windows_version.h"
+#include "skia/ext/platform_canvas.h"
+#include "skia/ext/skia_utils_win.h"
+#include "ui/aura/window.h"
+#include "ui/aura/window_tree_host.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/geometry/size.h"
+#include "ui/gfx/image/image.h"
+#include "ui/snapshot/snapshot.h"
+#include "ui/snapshot/snapshot_aura.h"
+
+namespace {
+
+// Windows 8.1 is the first version that supports PW_RENDERFULLCONTENT.
+// Without that flag PrintWindow may not correctly capture what's actually
+// onscreen.
+bool UseAuraSnapshot() {
+  return (base::win::GetVersion() < base::win::VERSION_WIN8_1);
+}
+
+}  // namespace
+
+namespace ui {
+
+namespace internal {
+
+bool GrabHwndSnapshot(HWND window_handle,
+                      const gfx::Rect& snapshot_bounds,

[sky, 2017/03/23 23:20:33]

Please name these in pixels.

+                      const gfx::Rect& clip_rect,
+                      gfx::Image* image) {
+  gfx::Rect snapshot_bounds_in_window =
+      snapshot_bounds + clip_rect.OffsetFromOrigin();
+  gfx::Size bitmap_size(snapshot_bounds_in_window.right(),
+                        snapshot_bounds_in_window.bottom());
+
+  std::unique_ptr<SkCanvas> canvas = skia::CreatePlatformCanvas(
+      bitmap_size.width(), bitmap_size.height(), false);
+  HDC mem_hdc = skia::GetNativeDrawingContext(canvas.get());
+
+  // Grab a copy of the window. Use PrintWindow because it works even when the
+  // window's partially occluded. The PW_RENDERFULLCONTENT flag is undocumented,
+  // but works starting in Windows 8.1. It allows for capturing the contents of
+  // the window that are drawn using DirectComposition.
+  UINT flags = PW_CLIENTONLY | PW_RENDERFULLCONTENT;
+
+  BOOL result = PrintWindow(window_handle, mem_hdc, flags);
+  if (!result) {
+    PLOG(ERROR) << "Failed to print window";
+    return false;
+  }
+
+  SkBitmap bitmap;
+  canvas->readPixels(gfx::RectToSkIRect(snapshot_bounds_in_window), &bitmap);
+
+  // Clear the region of the bitmap outside the clip rect to white.
+  SkCanvas image_canvas(bitmap);
+  SkPaint paint;
+  paint.setColor(SK_ColorWHITE);
+
+  SkRegion region;
+  gfx::Rect clip_in_bitmap(clip_rect.size());
+  clip_in_bitmap.Offset(-snapshot_bounds.OffsetFromOrigin());
+  region.setRect(gfx::RectToSkIRect(gfx::Rect(snapshot_bounds.size())));
+  region.op(gfx::RectToSkIRect(clip_in_bitmap), SkRegion::kDifference_Op);
+  image_canvas.drawRegion(region, paint);
+
+  *image = gfx::Image::CreateFrom1xBitmap(bitmap);
+
+  return true;
+}
+
+}  // namespace internal
+
+bool GrabViewSnapshot(gfx::NativeView view_handle,
+                      const gfx::Rect& snapshot_bounds,
+                      gfx::Image* image) {
+  return GrabWindowSnapshot(view_handle, snapshot_bounds, image);
+}
+
+bool GrabWindowSnapshot(gfx::NativeWindow window_handle,
+                        const gfx::Rect& snapshot_bounds,
+                        gfx::Image* image) {
+  if (UseAuraSnapshot()) {
+    // Not supported in Aura.  Callers should fall back to the async version.
+    return false;
+  }
+
+  DCHECK(window_handle);
+  gfx::Rect window_bounds = window_handle->GetBoundsInRootWindow();
+  aura::WindowTreeHost* host = window_handle->GetHost();
+  DCHECK(host);
+  HWND hwnd = host->GetAcceleratedWidget();
+  window_bounds.Intersect(host->window()->bounds());

[sky, 2017/03/23 23:20:33]

Can you get the bounds directly from the hwnd? I'm concerned the way you have it
now that you might end up with a size that is bigger than the size of the hwnd
(because of enclosing rect below).

+
+  gfx::RectF pixel_rect(window_bounds);
+  host->GetRootTransform().TransformRect(&pixel_rect);
+  gfx::RectF pixel_snapshot_bounds(snapshot_bounds);
+  host->GetRootTransform().TransformRect(&pixel_snapshot_bounds);
+
+  return internal::GrabHwndSnapshot(hwnd,
+                                    gfx::ToEnclosingRect(pixel_snapshot_bounds),
+                                    gfx::ToEnclosingRect(pixel_rect), image);
+}
+
+void GrabWindowSnapshotAsync(gfx::NativeWindow window,
+                             const gfx::Rect& source_rect,
+                             const GrabWindowSnapshotAsyncCallback& callback) {
+  if (UseAuraSnapshot()) {
+    GrabWindowSnapshotAsyncAura(window, source_rect, callback);
+    return;
+  }
+  gfx::Image image;
+  GrabWindowSnapshot(window, source_rect, &image);
+  callback.Run(image);
+}
+
+void GrabViewSnapshotAsync(gfx::NativeView view,
+                           const gfx::Rect& source_rect,
+                           const GrabWindowSnapshotAsyncCallback& callback) {
+  if (UseAuraSnapshot()) {
+    GrabWindowSnapshotAsyncAura(view, source_rect, callback);
+    return;
+  }
+  NOTIMPLEMENTED();
+  callback.Run(gfx::Image());
+}
+
+void GrabWindowSnapshotAndScaleAsync(
+    gfx::NativeWindow window,
+    const gfx::Rect& source_rect,
+    const gfx::Size& target_size,
+    scoped_refptr<base::TaskRunner> background_task_runner,
+    const GrabWindowSnapshotAsyncCallback& callback) {
+  if (UseAuraSnapshot()) {
+    GrabWindowSnapshotAndScaleAsyncAura(window, source_rect, target_size,
+                                        background_task_runner, callback);
+    return;
+  }
+  NOTIMPLEMENTED();
+  callback.Run(gfx::Image());
+}
+
+}  // namespace ui