TestFrameMetrics.cpp

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/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "gtest/gtest.h"

#include "FrameMetrics.h"

#include "mozilla/ScrollPositionUpdate.h"

using namespace mozilla;

using namespace mozilla::layers;

TEST(FrameMetricsTest, UpdatePendingScrollInfoKeepsVisualAndLayoutInSync)

  // The main thread clamps the scroll position in app units before sending it

  // as a ScrollPositionUpdate: 42576 - 18000 = 24576 app units, which converts

  // to 409.6 CSS pixels == 0x43cccccd. UpdatePendingScrollInfo sets the layout

  // scroll offset to that raw destination, but clamps the visual scroll offset

  // against CalculateScrollRange(), which subtracts *after* converting to CSS

  // pixels: FromAppUnits(42576) - FromAppUnits(18000) lands on 0x43cccccc (one

  // ULP lower, because 709.6 sits on the coarser 2^-14 grid of the [512, 1024)

  // binade). The destination is therefore one ULP above the CSS-space maximum

  // and gets clamped down. For non-root content the visual and layout offsets

  // must remain equal, so UpdatePendingScrollInfo adjusts the layout offset

  // so the invariant that the layout viewport encloses the visual viewport

  // continues to hold.

  FrameMetrics metrics;

  // mIsRootContent defaults to false, so the visual/layout relative offset must

  // remain zero.

  ASSERT_FALSE(metrics.IsRootContent());

  metrics.SetZoom(CSSToParentLayerScale(1.0f));

  metrics.SetScrollableRect(CSSRect(0, 0, 1000, CSSPixel::FromAppUnits(42576)));

  metrics.SetCompositionBounds(

      ParentLayerRect(0, 0, 1000, CSSPixel::FromAppUnits(18000)));

  ScrollPositionUpdate update =

      ScrollPositionUpdate::NewScroll(ScrollOrigin::Other, nsPoint(0, 24576));

  metrics.UpdatePendingScrollInfo(update);

  // The visual and layout offsets must stay equal for non-root content.

  EXPECT_EQ(metrics.GetVisualScrollOffset(), metrics.GetLayoutScrollOffset());

  // A second update reads back the offsets to compute the relative offset; with

  // the offsets kept in sync it stays zero and does not trip the assertion in

  // UpdatePendingScrollInfo.

  metrics.UpdatePendingScrollInfo(update);

  EXPECT_EQ(metrics.GetVisualScrollOffset(), metrics.GetLayoutScrollOffset());