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481 lines
28 KiB
Java
481 lines
28 KiB
Java
/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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package org.mozilla.gecko.gfx;
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import android.graphics.PointF;
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import android.graphics.RectF;
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import android.util.Log;
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import org.mozilla.gecko.FloatUtils;
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import org.mozilla.gecko.GeckoAppShell;
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final class DisplayPortCalculator {
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private static final String LOGTAG = "GeckoDisplayPortCalculator";
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private static final PointF ZERO_VELOCITY = new PointF(0, 0);
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private static DisplayPortStrategy sStrategy = new VelocityBiasStrategy();
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static DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) {
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return sStrategy.calculate(metrics, (velocity == null ? ZERO_VELOCITY : velocity));
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}
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static boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) {
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if (displayPort == null) {
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return true;
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}
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return sStrategy.aboutToCheckerboard(metrics, (velocity == null ? ZERO_VELOCITY : velocity), displayPort);
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}
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/**
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* Set the active strategy to use.
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* See the gfx.displayport.strategy pref in mobile/android/app/mobile.js to see the
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* mapping between ints and strategies.
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*/
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static void setStrategy(int strategy) {
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switch (strategy) {
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case 0:
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default:
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sStrategy = new FixedMarginStrategy();
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break;
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case 1:
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sStrategy = new VelocityBiasStrategy();
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break;
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case 2:
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sStrategy = new DynamicResolutionStrategy();
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break;
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case 3:
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sStrategy = new NoMarginStrategy();
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break;
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}
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Log.i(LOGTAG, "Set strategy " + sStrategy.getClass().getName());
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}
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private interface DisplayPortStrategy {
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/** Calculates a displayport given a viewport and panning velocity. */
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public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity);
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/** Returns true if a checkerboard is about to be visible and we should not throttle drawing. */
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public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort);
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}
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/**
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* Return the dimensions for a rect that has area (width*height) that does not exceed the page size in the
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* given metrics object. The area in the returned FloatSize may be less than width*height if the page is
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* small, but it will never be larger than width*height.
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* Note that this process may change the relative aspect ratio of the given dimensions.
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*/
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private static FloatSize reshapeForPage(float width, float height, ImmutableViewportMetrics metrics) {
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// figure out how much of the desired buffer amount we can actually use on the horizontal axis
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float usableWidth = Math.min(width, metrics.pageSizeWidth);
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// if we reduced the buffer amount on the horizontal axis, we should take that saved memory and
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// use it on the vertical axis
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float extraUsableHeight = (float)Math.floor(((width - usableWidth) * height) / usableWidth);
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float usableHeight = Math.min(height + extraUsableHeight, metrics.pageSizeHeight);
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if (usableHeight < height && usableWidth == width) {
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// and the reverse - if we shrunk the buffer on the vertical axis we can add it to the horizontal
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float extraUsableWidth = (float)Math.floor(((height - usableHeight) * width) / usableHeight);
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usableWidth = Math.min(width + extraUsableWidth, metrics.pageSizeWidth);
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}
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return new FloatSize(usableWidth, usableHeight);
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}
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/**
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* Expand the given rect in all directions by a "danger zone". The size of the danger zone on an axis
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* is the size of the view on that axis multiplied by the given multiplier. The expanded rect is then
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* clamped to page bounds and returned.
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*/
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private static RectF expandByDangerZone(RectF rect, float dangerZoneXMultiplier, float dangerZoneYMultiplier, ImmutableViewportMetrics metrics) {
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// calculate the danger zone amounts in pixels
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float dangerZoneX = metrics.getWidth() * dangerZoneXMultiplier;
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float dangerZoneY = metrics.getHeight() * dangerZoneYMultiplier;
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rect = RectUtils.expand(rect, dangerZoneX, dangerZoneY);
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// clamp to page bounds
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if (rect.top < 0) rect.top = 0;
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if (rect.left < 0) rect.left = 0;
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if (rect.right > metrics.pageSizeWidth) rect.right = metrics.pageSizeWidth;
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if (rect.bottom > metrics.pageSizeHeight) rect.bottom = metrics.pageSizeHeight;
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return rect;
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}
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/**
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* Adjust the given margins so if they are applied on the viewport in the metrics, the resulting rect
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* does not exceed the page bounds. This code will maintain the total margin amount for a given axis;
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* it assumes that margins.left + metrics.getWidth() + margins.right is less than or equal to
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* metrics.pageSizeWidth; and the same for the y axis.
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*/
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private static RectF shiftMarginsForPageBounds(RectF margins, ImmutableViewportMetrics metrics) {
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// check how much we're overflowing in each direction. note that at most one of leftOverflow
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// and rightOverflow can be greater than zero, and at most one of topOverflow and bottomOverflow
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// can be greater than zero, because of the assumption described in the method javadoc.
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float leftOverflow = margins.left - metrics.viewportRectLeft;
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float rightOverflow = margins.right - (metrics.pageSizeWidth - metrics.viewportRectRight);
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float topOverflow = margins.top - metrics.viewportRectTop;
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float bottomOverflow = margins.bottom - (metrics.pageSizeHeight - metrics.viewportRectBottom);
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// if the margins overflow the page bounds, shift them to other side on the same axis
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if (leftOverflow > 0) {
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margins.left -= leftOverflow;
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margins.right += leftOverflow;
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} else if (rightOverflow > 0) {
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margins.right -= rightOverflow;
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margins.left += rightOverflow;
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}
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if (topOverflow > 0) {
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margins.top -= topOverflow;
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margins.bottom += topOverflow;
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} else if (bottomOverflow > 0) {
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margins.bottom -= bottomOverflow;
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margins.top += bottomOverflow;
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}
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return margins;
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}
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/**
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* This class implements the variation where we basically don't bother with a a display port.
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*/
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private static class NoMarginStrategy implements DisplayPortStrategy {
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public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) {
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return new DisplayPortMetrics(metrics.viewportRectLeft,
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metrics.viewportRectTop,
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metrics.viewportRectRight,
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metrics.viewportRectBottom,
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metrics.zoomFactor);
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}
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public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) {
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return true;
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}
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}
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/**
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* This class implements the variation where we use a fixed-size margin on the display port.
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* The margin is always 300 pixels in all directions, except when we are (a) approaching a page
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* boundary, and/or (b) if we are limited by the page size. In these cases we try to maintain
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* the area of the display port by (a) shifting the buffer to the other side on the same axis,
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* and/or (b) increasing the buffer on the other axis to compensate for the reduced buffer on
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* one axis.
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*/
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private static class FixedMarginStrategy implements DisplayPortStrategy {
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// The length of each axis of the display port will be the corresponding view length
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// multiplied by this factor.
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private static final float SIZE_MULTIPLIER = 1.5f;
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// If the visible rect is within the danger zone (measured as a fraction of the view size
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// from the edge of the displayport) we start redrawing to minimize checkerboarding.
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private static final float DANGER_ZONE_X_MULTIPLIER = 0.10f;
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private static final float DANGER_ZONE_Y_MULTIPLIER = 0.20f;
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public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) {
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float displayPortWidth = metrics.getWidth() * SIZE_MULTIPLIER;
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float displayPortHeight = metrics.getHeight() * SIZE_MULTIPLIER;
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// we need to avoid having a display port that is larger than the page, or we will end up
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// painting things outside the page bounds (bug 729169). we simultaneously need to make
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// the display port as large as possible so that we redraw less. reshape the display
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// port dimensions to accomplish this.
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FloatSize usableSize = reshapeForPage(displayPortWidth, displayPortHeight, metrics);
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float horizontalBuffer = usableSize.width - metrics.getWidth();
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float verticalBuffer = usableSize.height - metrics.getHeight();
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// and now calculate the display port margins based on how much buffer we've decided to use and
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// the page bounds, ensuring we use all of the available buffer amounts on one side or the other
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// on any given axis. (i.e. if we're scrolled to the top of the page, the vertical buffer is
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// entirely below the visible viewport, but if we're halfway down the page, the vertical buffer
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// is split).
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RectF margins = new RectF();
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margins.left = horizontalBuffer / 2.0f;
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margins.right = horizontalBuffer - margins.left;
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margins.top = verticalBuffer / 2.0f;
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margins.bottom = verticalBuffer - margins.top;
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margins = shiftMarginsForPageBounds(margins, metrics);
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// note that unless the viewport size changes, or the page dimensions change (either because of
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// content changes or zooming), the size of the display port should remain constant. this
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// is intentional to avoid re-creating textures and all sorts of other reallocations in the
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// draw and composition code.
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return new DisplayPortMetrics(metrics.viewportRectLeft - margins.left,
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metrics.viewportRectTop - margins.top,
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metrics.viewportRectRight + margins.right,
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metrics.viewportRectBottom + margins.bottom,
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metrics.zoomFactor);
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}
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public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) {
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// Increase the size of the viewport based on the danger zone multiplier (and clamp to page
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// boundaries), and intersect it with the current displayport to determine whether we're
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// close to checkerboarding.
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RectF adjustedViewport = expandByDangerZone(metrics.getViewport(), DANGER_ZONE_X_MULTIPLIER, DANGER_ZONE_Y_MULTIPLIER, metrics);
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return !displayPort.contains(adjustedViewport);
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}
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}
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/**
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* This class implements the variation with a small fixed-size margin with velocity bias.
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* In this variation, the default margins are pretty small relative to the view size, but
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* they are affected by the panning velocity. Specifically, if we are panning on one axis,
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* we remove the margins on the other axis because we are likely axis-locked. Also once
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* we are panning in one direction above a certain threshold velocity, we shift the buffer
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* so that it is almost entirely in the direction of the pan, with a little bit in the
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* reverse direction.
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*/
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private static class VelocityBiasStrategy implements DisplayPortStrategy {
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// The length of each axis of the display port will be the corresponding view length
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// multiplied by this factor.
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private static final float SIZE_MULTIPLIER = 1.5f;
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// The velocity above which we apply the velocity bias
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private static final float VELOCITY_THRESHOLD = GeckoAppShell.getDpi() / 32f;
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// How much of the buffer to keep in the reverse direction of the velocity
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private static final float REVERSE_BUFFER = 0.2f;
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public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) {
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float displayPortWidth = metrics.getWidth() * SIZE_MULTIPLIER;
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float displayPortHeight = metrics.getHeight() * SIZE_MULTIPLIER;
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// but if we're panning on one axis, set the margins for the other axis to zero since we are likely
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// axis locked and won't be displaying that extra area.
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if (Math.abs(velocity.x) > VELOCITY_THRESHOLD && FloatUtils.fuzzyEquals(velocity.y, 0)) {
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displayPortHeight = metrics.getHeight();
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} else if (Math.abs(velocity.y) > VELOCITY_THRESHOLD && FloatUtils.fuzzyEquals(velocity.x, 0)) {
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displayPortWidth = metrics.getWidth();
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}
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// we need to avoid having a display port that is larger than the page, or we will end up
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// painting things outside the page bounds (bug 729169).
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displayPortWidth = Math.min(displayPortWidth, metrics.pageSizeWidth);
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displayPortHeight = Math.min(displayPortHeight, metrics.pageSizeHeight);
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float horizontalBuffer = displayPortWidth - metrics.getWidth();
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float verticalBuffer = displayPortHeight - metrics.getHeight();
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// if we're panning above the VELOCITY_THRESHOLD on an axis, apply the margin so that it
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// is entirely in the direction of panning. Otherwise, split the margin evenly on both sides of
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// the display port.
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RectF margins = new RectF();
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if (velocity.x > VELOCITY_THRESHOLD) {
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margins.left = horizontalBuffer * REVERSE_BUFFER;
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} else if (velocity.x < -VELOCITY_THRESHOLD) {
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margins.left = horizontalBuffer * (1.0f - REVERSE_BUFFER);
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} else {
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margins.left = horizontalBuffer / 2.0f;
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}
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margins.right = horizontalBuffer - margins.left;
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if (velocity.y > VELOCITY_THRESHOLD) {
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margins.top = verticalBuffer * REVERSE_BUFFER;
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} else if (velocity.y < -VELOCITY_THRESHOLD) {
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margins.top = verticalBuffer * (1.0f - REVERSE_BUFFER);
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} else {
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margins.top = verticalBuffer / 2.0f;
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}
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margins.bottom = verticalBuffer - margins.top;
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// and finally shift the margins to account for page bounds
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margins = shiftMarginsForPageBounds(margins, metrics);
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return new DisplayPortMetrics(metrics.viewportRectLeft - margins.left,
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metrics.viewportRectTop - margins.top,
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metrics.viewportRectRight + margins.right,
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metrics.viewportRectBottom + margins.bottom,
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metrics.zoomFactor);
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}
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public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) {
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// Since we have such a small margin, we want to be drawing more aggressively. At the start of a
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// pan the velocity is going to be large so we're almost certainly going to go into checkerboard
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// on every frame, so drawing all the time seems like the right thing. At the end of the pan we
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// want to re-center the displayport and draw stuff on all sides, so again we don't want to throttle
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// there. When we're not panning we're not drawing anyway so it doesn't make a difference there.
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return true;
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}
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}
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/**
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* This class implements the variation where we draw more of the page at low resolution while panning.
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* In this variation, as we pan faster, we increase the page area we are drawing, but reduce the draw
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* resolution to compensate. This results in the same device-pixel area drawn; the compositor then
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* scales this up to the viewport zoom level. This results in a large area of the page drawn but it
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* looks blurry. The assumption is that drawing extra that we never display is better than checkerboarding,
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* where we draw less but never even show it on the screen.
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*/
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private static class DynamicResolutionStrategy implements DisplayPortStrategy {
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// The length of each axis of the display port will be the corresponding view length
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// multiplied by this factor.
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private static final float SIZE_MULTIPLIER = 1.5f;
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// The velocity above which we start zooming out the display port to keep up
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// with the panning.
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private static final float VELOCITY_EXPANSION_THRESHOLD = GeckoAppShell.getDpi() / 16f;
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// How much we increase the display port based on velocity. Assuming no friction and
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// splitting (see below), this should be be the number of frames (@60fps) between us
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// calculating the display port and the draw of the *next* display port getting composited
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// and displayed on the screen. This is because the timeline looks like this:
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// Java: pan pan pan pan pan pan ! pan pan pan pan pan pan !
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// Gecko: \-> draw -> composite / \-> draw -> composite /
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// The display port calculated on the first "pan" gets composited to the screen at the
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// first exclamation mark, and remains on the screen until the second exclamation mark.
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// In order to avoid checkerboarding, that display port must be able to contain all of
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// the panning until the second exclamation mark, which encompasses two entire draw/composite
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// cycles.
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// If we take into account friction, our velocity multiplier should be reduced as the
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// amount of pan will decrease each time. If we take into account display port splitting,
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// it should be increased as the splitting means some of the display port will be used to
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// draw in the opposite direction of the velocity. For now I'm assuming these two cancel
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// each other out.
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private static final float VELOCITY_MULTIPLIER = 60.0f;
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// The following constants adjust how biased the display port is in the direction of panning.
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// When panning fast (above the FAST_THRESHOLD) we use the fast split factor to split the
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// display port "buffer" area, otherwise we use the slow split factor. This is based on the
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// assumption that if the user is panning fast, they are less likely to reverse directions
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// and go backwards, so we should spend more of our display port buffer in the direction of
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// panning.
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private static final float VELOCITY_FAST_THRESHOLD = VELOCITY_EXPANSION_THRESHOLD * 2.0f;
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private static final float FAST_SPLIT_FACTOR = 0.95f;
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private static final float SLOW_SPLIT_FACTOR = 0.8f;
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// The following constants are used for viewport prediction; we use them to estimate where
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// the viewport will be soon and whether or not we should trigger a draw right now. "soon"
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// in the previous sentence really refers to the amount of time it would take to draw and
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// composite from the point at which we do the calculation, and that is not really a known
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// quantity. The velocity multiplier is how much we multiply the velocity by; it has the
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// same caveats as the VELOCITY_MULTIPLIER above except that it only needs to take into account
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// one draw/composite cycle instead of two. The danger zone multiplier is a multiplier of the
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// viewport size that we use as an extra "danger zone" around the viewport; if this danger
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// zone falls outside the display port then we are approaching the point at which we will
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// checkerboard, and hence should start drawing. Note that if DANGER_ZONE_MULTIPLIER is
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// greater than (SIZE_MULTIPLIER - 1.0f), then at zero velocity we will always be in the
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// danger zone, and thus will be constantly drawing.
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private static final float PREDICTION_VELOCITY_MULTIPLIER = 30.0f;
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private static final float DANGER_ZONE_MULTIPLIER = 0.20f; // must be less than (SIZE_MULTIPLIER - 1.0f)
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public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) {
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float displayPortWidth = metrics.getWidth() * SIZE_MULTIPLIER;
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float displayPortHeight = metrics.getHeight() * SIZE_MULTIPLIER;
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// for resolution calculation purposes, we need to know what the adjusted display port dimensions
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// would be if we had zero velocity, so calculate that here before we increase the display port
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// based on velocity.
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FloatSize reshapedSize = reshapeForPage(displayPortWidth, displayPortHeight, metrics);
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// increase displayPortWidth and displayPortHeight based on the velocity, but maintaining their
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// relative aspect ratio.
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if (velocity.length() > VELOCITY_EXPANSION_THRESHOLD) {
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float velocityFactor = Math.max(Math.abs(velocity.x) / displayPortWidth,
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Math.abs(velocity.y) / displayPortHeight);
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velocityFactor *= VELOCITY_MULTIPLIER;
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displayPortWidth += (displayPortWidth * velocityFactor);
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displayPortHeight += (displayPortHeight * velocityFactor);
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}
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// at this point, displayPortWidth and displayPortHeight are how much of the page (in device pixels)
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// we want to be rendered by Gecko. Note here "device pixels" is equivalent to CSS pixels multiplied
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// by metrics.zoomFactor
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// we need to avoid having a display port that is larger than the page, or we will end up
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// painting things outside the page bounds (bug 729169). we simultaneously need to make
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// the display port as large as possible so that we redraw less. reshape the display
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// port dimensions to accomplish this. this may change the aspect ratio of the display port,
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// but we are assuming that this is desirable because the advantages from pre-drawing will
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// outweigh the disadvantages from any buffer reallocations that might occur.
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FloatSize usableSize = reshapeForPage(displayPortWidth, displayPortHeight, metrics);
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float horizontalBuffer = usableSize.width - metrics.getWidth();
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float verticalBuffer = usableSize.height - metrics.getHeight();
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// at this point, horizontalBuffer and verticalBuffer are the dimensions of the buffer area we have.
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// the buffer area is the off-screen area that is part of the display port and will be pre-drawn in case
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// the user scrolls there. we now need to split the buffer area on each axis so that we know
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// what the exact margins on each side will be. first we split the buffer amount based on the direction
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// we're moving, so that we have a larger buffer in the direction of travel.
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RectF margins = new RectF();
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margins.left = splitBufferByVelocity(horizontalBuffer, velocity.x);
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margins.right = horizontalBuffer - margins.left;
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margins.top = splitBufferByVelocity(verticalBuffer, velocity.y);
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margins.bottom = verticalBuffer - margins.top;
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// then, we account for running into the page bounds - so that if we hit the top of the page, we need
|
|
// to drop the top margin and move that amount to the bottom margin.
|
|
margins = shiftMarginsForPageBounds(margins, metrics);
|
|
|
|
// finally, we calculate the resolution we want to render the display port area at. We do this
|
|
// so that as we expand the display port area (because of velocity), we reduce the resolution of
|
|
// the painted area so as to maintain the size of the buffer Gecko is painting into. we calculate
|
|
// the reduction in resolution by comparing the display port size with and without the velocity
|
|
// changes applied.
|
|
// this effectively means that as we pan faster and faster, the display port grows, but we paint
|
|
// at lower resolutions. this paints more area to reduce checkerboard at the cost of increasing
|
|
// compositor-scaling and blurriness. Once we stop panning, the blurriness must be entirely gone.
|
|
// Note that usable* could be less than base* if we are pinch-zoomed out into overscroll, so we
|
|
// clamp it to make sure this doesn't increase our display resolution past metrics.zoomFactor.
|
|
float scaleFactor = Math.min(reshapedSize.width / usableSize.width, reshapedSize.height / usableSize.height);
|
|
float displayResolution = metrics.zoomFactor * Math.min(1.0f, scaleFactor);
|
|
|
|
DisplayPortMetrics dpMetrics = new DisplayPortMetrics(
|
|
metrics.viewportRectLeft - margins.left,
|
|
metrics.viewportRectTop - margins.top,
|
|
metrics.viewportRectRight + margins.right,
|
|
metrics.viewportRectBottom + margins.bottom,
|
|
displayResolution);
|
|
return dpMetrics;
|
|
}
|
|
|
|
/**
|
|
* Split the given buffer amount into two based on the velocity.
|
|
* Given an amount of total usable buffer on an axis, this will
|
|
* return the amount that should be used on the left/top side of
|
|
* the axis (the side which a negative velocity vector corresponds
|
|
* to).
|
|
*/
|
|
private float splitBufferByVelocity(float amount, float velocity) {
|
|
// if no velocity, so split evenly
|
|
if (FloatUtils.fuzzyEquals(velocity, 0)) {
|
|
return amount / 2.0f;
|
|
}
|
|
// if we're moving quickly, assign more of the amount in that direction
|
|
// since is is less likely that we will reverse direction immediately
|
|
if (velocity < -VELOCITY_FAST_THRESHOLD) {
|
|
return amount * FAST_SPLIT_FACTOR;
|
|
}
|
|
if (velocity > VELOCITY_FAST_THRESHOLD) {
|
|
return amount * (1.0f - FAST_SPLIT_FACTOR);
|
|
}
|
|
// if we're moving slowly, then assign less of the amount in that direction
|
|
if (velocity < 0) {
|
|
return amount * SLOW_SPLIT_FACTOR;
|
|
} else {
|
|
return amount * (1.0f - SLOW_SPLIT_FACTOR);
|
|
}
|
|
}
|
|
|
|
public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) {
|
|
// Expand the viewport based on our velocity (and clamp it to page boundaries).
|
|
// Then intersect it with the last-requested displayport to determine whether we're
|
|
// close to checkerboarding.
|
|
|
|
RectF predictedViewport = metrics.getViewport();
|
|
|
|
// first we expand the viewport in the direction we're moving based on some
|
|
// multiple of the current velocity.
|
|
if (velocity.length() > 0) {
|
|
if (velocity.x < 0) {
|
|
predictedViewport.left += velocity.x * PREDICTION_VELOCITY_MULTIPLIER;
|
|
} else if (velocity.x > 0) {
|
|
predictedViewport.right += velocity.x * PREDICTION_VELOCITY_MULTIPLIER;
|
|
}
|
|
|
|
if (velocity.y < 0) {
|
|
predictedViewport.top += velocity.y * PREDICTION_VELOCITY_MULTIPLIER;
|
|
} else if (velocity.y > 0) {
|
|
predictedViewport.bottom += velocity.y * PREDICTION_VELOCITY_MULTIPLIER;
|
|
}
|
|
}
|
|
|
|
// then we expand the viewport evenly in all directions just to have an extra
|
|
// safety zone. this also clamps it to page bounds.
|
|
predictedViewport = expandByDangerZone(predictedViewport, DANGER_ZONE_MULTIPLIER, DANGER_ZONE_MULTIPLIER, metrics);
|
|
return !displayPort.contains(predictedViewport);
|
|
}
|
|
}
|
|
}
|