/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*- * 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/. */ package org.mozilla.gecko.gfx; import org.mozilla.gecko.GeckoAppShell; import org.mozilla.gecko.PrefsHelper; import org.mozilla.gecko.util.FloatUtils; import org.json.JSONArray; import android.graphics.PointF; import android.graphics.RectF; import android.util.FloatMath; import android.util.Log; import java.util.HashMap; import java.util.Map; final class DisplayPortCalculator { private static final String LOGTAG = "GeckoDisplayPort"; private static final PointF ZERO_VELOCITY = new PointF(0, 0); // Keep this in sync with the TILEDLAYERBUFFER_TILE_SIZE defined in gfx/layers/TiledLayerBuffer.h private static final int TILE_SIZE = 256; private static final String PREF_DISPLAYPORT_STRATEGY = "gfx.displayport.strategy"; private static final String PREF_DISPLAYPORT_FM_MULTIPLIER = "gfx.displayport.strategy_fm.multiplier"; private static final String PREF_DISPLAYPORT_FM_DANGER_X = "gfx.displayport.strategy_fm.danger_x"; private static final String PREF_DISPLAYPORT_FM_DANGER_Y = "gfx.displayport.strategy_fm.danger_y"; private static final String PREF_DISPLAYPORT_VB_MULTIPLIER = "gfx.displayport.strategy_vb.multiplier"; private static final String PREF_DISPLAYPORT_VB_VELOCITY_THRESHOLD = "gfx.displayport.strategy_vb.threshold"; private static final String PREF_DISPLAYPORT_VB_REVERSE_BUFFER = "gfx.displayport.strategy_vb.reverse_buffer"; private static final String PREF_DISPLAYPORT_VB_DANGER_X_BASE = "gfx.displayport.strategy_vb.danger_x_base"; private static final String PREF_DISPLAYPORT_VB_DANGER_Y_BASE = "gfx.displayport.strategy_vb.danger_y_base"; private static final String PREF_DISPLAYPORT_VB_DANGER_X_INCR = "gfx.displayport.strategy_vb.danger_x_incr"; private static final String PREF_DISPLAYPORT_VB_DANGER_Y_INCR = "gfx.displayport.strategy_vb.danger_y_incr"; private static final String PREF_DISPLAYPORT_PB_VELOCITY_THRESHOLD = "gfx.displayport.strategy_pb.threshold"; private static DisplayPortStrategy sStrategy = new VelocityBiasStrategy(null); static DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) { return sStrategy.calculate(metrics, (velocity == null ? ZERO_VELOCITY : velocity)); } static boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) { if (displayPort == null) { return true; } return sStrategy.aboutToCheckerboard(metrics, (velocity == null ? ZERO_VELOCITY : velocity), displayPort); } static boolean drawTimeUpdate(long millis, int pixels) { return sStrategy.drawTimeUpdate(millis, pixels); } static void resetPageState() { sStrategy.resetPageState(); } static void initPrefs() { JSONArray prefs = new JSONArray(); prefs.put(PREF_DISPLAYPORT_STRATEGY); prefs.put(PREF_DISPLAYPORT_FM_MULTIPLIER); prefs.put(PREF_DISPLAYPORT_FM_DANGER_X); prefs.put(PREF_DISPLAYPORT_FM_DANGER_Y); prefs.put(PREF_DISPLAYPORT_VB_MULTIPLIER); prefs.put(PREF_DISPLAYPORT_VB_VELOCITY_THRESHOLD); prefs.put(PREF_DISPLAYPORT_VB_REVERSE_BUFFER); prefs.put(PREF_DISPLAYPORT_VB_DANGER_X_BASE); prefs.put(PREF_DISPLAYPORT_VB_DANGER_Y_BASE); prefs.put(PREF_DISPLAYPORT_VB_DANGER_X_INCR); prefs.put(PREF_DISPLAYPORT_VB_DANGER_Y_INCR); prefs.put(PREF_DISPLAYPORT_PB_VELOCITY_THRESHOLD); PrefsHelper.getPrefs(prefs, new PrefsHelper.PrefHandlerBase() { private Map mValues = new HashMap(); @Override public void prefValue(String pref, int value) { mValues.put(pref, value); } @Override public void finish() { setStrategy(mValues); } }); } /** * Set the active strategy to use. * See the gfx.displayport.strategy pref in mobile/android/app/mobile.js to see the * mapping between ints and strategies. */ static boolean setStrategy(Map prefs) { Integer strategy = prefs.get(PREF_DISPLAYPORT_STRATEGY); if (strategy == null) { return false; } switch (strategy) { case 0: sStrategy = new FixedMarginStrategy(prefs); break; case 1: sStrategy = new VelocityBiasStrategy(prefs); break; case 2: sStrategy = new DynamicResolutionStrategy(prefs); break; case 3: sStrategy = new NoMarginStrategy(prefs); break; case 4: sStrategy = new PredictionBiasStrategy(prefs); break; default: Log.e(LOGTAG, "Invalid strategy index specified"); return false; } Log.i(LOGTAG, "Set strategy " + sStrategy.toString()); return true; } private static float getFloatPref(Map prefs, String prefName, int defaultValue) { Integer value = (prefs == null ? null : prefs.get(prefName)); return (float)(value == null || value < 0 ? defaultValue : value) / 1000f; } private static abstract class DisplayPortStrategy { /** Calculates a displayport given a viewport and panning velocity. */ public abstract DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity); /** Returns true if a checkerboard is about to be visible and we should not throttle drawing. */ public abstract boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort); /** Notify the strategy of a new recorded draw time. Return false to turn off draw time recording. */ public boolean drawTimeUpdate(long millis, int pixels) { return false; } /** Reset any page-specific state stored, as the page being displayed has changed. */ public void resetPageState() {} } /** * Return the dimensions for a rect that has area (width*height) that does not exceed the page size in the * given metrics object. The area in the returned FloatSize may be less than width*height if the page is * small, but it will never be larger than width*height. * Note that this process may change the relative aspect ratio of the given dimensions. */ private static FloatSize reshapeForPage(float width, float height, ImmutableViewportMetrics metrics) { // figure out how much of the desired buffer amount we can actually use on the horizontal axis float usableWidth = Math.min(width, metrics.getPageWidth()); // if we reduced the buffer amount on the horizontal axis, we should take that saved memory and // use it on the vertical axis float extraUsableHeight = (float)Math.floor(((width - usableWidth) * height) / usableWidth); float usableHeight = Math.min(height + extraUsableHeight, metrics.getPageHeight()); if (usableHeight < height && usableWidth == width) { // and the reverse - if we shrunk the buffer on the vertical axis we can add it to the horizontal float extraUsableWidth = (float)Math.floor(((height - usableHeight) * width) / usableHeight); usableWidth = Math.min(width + extraUsableWidth, metrics.getPageWidth()); } return new FloatSize(usableWidth, usableHeight); } /** * Expand the given rect in all directions by a "danger zone". The size of the danger zone on an axis * is the size of the view on that axis multiplied by the given multiplier. The expanded rect is then * clamped to page bounds and returned. */ private static RectF expandByDangerZone(RectF rect, float dangerZoneXMultiplier, float dangerZoneYMultiplier, ImmutableViewportMetrics metrics) { // calculate the danger zone amounts in pixels float dangerZoneX = metrics.getWidth() * dangerZoneXMultiplier; float dangerZoneY = metrics.getHeight() * dangerZoneYMultiplier; rect = RectUtils.expand(rect, dangerZoneX, dangerZoneY); // clamp to page bounds return clampToPageBounds(rect, metrics); } /** * Expand the given margins such that when they are applied on the viewport, the resulting rect * does not have any partial tiles, except when it is clipped by the page bounds. This assumes * the tiles are TILE_SIZE by TILE_SIZE and start at the origin, such that there will always be * a tile at (0,0)-(TILE_SIZE,TILE_SIZE)). */ private static DisplayPortMetrics getTileAlignedDisplayPortMetrics(RectF margins, float zoom, ImmutableViewportMetrics metrics) { float left = metrics.viewportRectLeft - margins.left; float top = metrics.viewportRectTop - margins.top; float right = metrics.viewportRectRight + margins.right; float bottom = metrics.viewportRectBottom + margins.bottom; left = Math.max(metrics.pageRectLeft, TILE_SIZE * FloatMath.floor(left / TILE_SIZE)); top = Math.max(metrics.pageRectTop, TILE_SIZE * FloatMath.floor(top / TILE_SIZE)); right = Math.min(metrics.pageRectRight, TILE_SIZE * FloatMath.ceil(right / TILE_SIZE)); bottom = Math.min(metrics.pageRectBottom, TILE_SIZE * FloatMath.ceil(bottom / TILE_SIZE)); return new DisplayPortMetrics(left, top, right, bottom, zoom); } /** * Adjust the given margins so if they are applied on the viewport in the metrics, the resulting rect * does not exceed the page bounds. This code will maintain the total margin amount for a given axis; * it assumes that margins.left + metrics.getWidth() + margins.right is less than or equal to * metrics.getPageWidth(); and the same for the y axis. */ private static RectF shiftMarginsForPageBounds(RectF margins, ImmutableViewportMetrics metrics) { // check how much we're overflowing in each direction. note that at most one of leftOverflow // and rightOverflow can be greater than zero, and at most one of topOverflow and bottomOverflow // can be greater than zero, because of the assumption described in the method javadoc. float leftOverflow = metrics.pageRectLeft - (metrics.viewportRectLeft - margins.left); float rightOverflow = (metrics.viewportRectRight + margins.right) - metrics.pageRectRight; float topOverflow = metrics.pageRectTop - (metrics.viewportRectTop - margins.top); float bottomOverflow = (metrics.viewportRectBottom + margins.bottom) - metrics.pageRectBottom; // if the margins overflow the page bounds, shift them to other side on the same axis if (leftOverflow > 0) { margins.left -= leftOverflow; margins.right += leftOverflow; } else if (rightOverflow > 0) { margins.right -= rightOverflow; margins.left += rightOverflow; } if (topOverflow > 0) { margins.top -= topOverflow; margins.bottom += topOverflow; } else if (bottomOverflow > 0) { margins.bottom -= bottomOverflow; margins.top += bottomOverflow; } return margins; } /** * Clamp the given rect to the page bounds and return it. */ private static RectF clampToPageBounds(RectF rect, ImmutableViewportMetrics metrics) { if (rect.top < metrics.pageRectTop) rect.top = metrics.pageRectTop; if (rect.left < metrics.pageRectLeft) rect.left = metrics.pageRectLeft; if (rect.right > metrics.pageRectRight) rect.right = metrics.pageRectRight; if (rect.bottom > metrics.pageRectBottom) rect.bottom = metrics.pageRectBottom; return rect; } /** * This class implements the variation where we basically don't bother with a a display port. */ private static class NoMarginStrategy extends DisplayPortStrategy { NoMarginStrategy(Map prefs) { // no prefs in this strategy } @Override public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) { return new DisplayPortMetrics(metrics.viewportRectLeft, metrics.viewportRectTop, metrics.viewportRectRight, metrics.viewportRectBottom, metrics.zoomFactor); } @Override public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) { return true; } @Override public String toString() { return "NoMarginStrategy"; } } /** * This class implements the variation where we use a fixed-size margin on the display port. * The margin is always 300 pixels in all directions, except when we are (a) approaching a page * boundary, and/or (b) if we are limited by the page size. In these cases we try to maintain * the area of the display port by (a) shifting the buffer to the other side on the same axis, * and/or (b) increasing the buffer on the other axis to compensate for the reduced buffer on * one axis. */ private static class FixedMarginStrategy extends DisplayPortStrategy { // The length of each axis of the display port will be the corresponding view length // multiplied by this factor. private final float SIZE_MULTIPLIER; // If the visible rect is within the danger zone (measured as a fraction of the view size // from the edge of the displayport) we start redrawing to minimize checkerboarding. private final float DANGER_ZONE_X_MULTIPLIER; private final float DANGER_ZONE_Y_MULTIPLIER; FixedMarginStrategy(Map prefs) { SIZE_MULTIPLIER = getFloatPref(prefs, PREF_DISPLAYPORT_FM_MULTIPLIER, 2000); DANGER_ZONE_X_MULTIPLIER = getFloatPref(prefs, PREF_DISPLAYPORT_FM_DANGER_X, 100); DANGER_ZONE_Y_MULTIPLIER = getFloatPref(prefs, PREF_DISPLAYPORT_FM_DANGER_Y, 200); } @Override public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) { float displayPortWidth = metrics.getWidth() * SIZE_MULTIPLIER; float displayPortHeight = metrics.getHeight() * SIZE_MULTIPLIER; // we need to avoid having a display port that is larger than the page, or we will end up // painting things outside the page bounds (bug 729169). we simultaneously need to make // the display port as large as possible so that we redraw less. reshape the display // port dimensions to accomplish this. FloatSize usableSize = reshapeForPage(displayPortWidth, displayPortHeight, metrics); float horizontalBuffer = usableSize.width - metrics.getWidth(); float verticalBuffer = usableSize.height - metrics.getHeight(); // and now calculate the display port margins based on how much buffer we've decided to use and // the page bounds, ensuring we use all of the available buffer amounts on one side or the other // on any given axis. (i.e. if we're scrolled to the top of the page, the vertical buffer is // entirely below the visible viewport, but if we're halfway down the page, the vertical buffer // is split). RectF margins = new RectF(); margins.left = horizontalBuffer / 2.0f; margins.right = horizontalBuffer - margins.left; margins.top = verticalBuffer / 2.0f; margins.bottom = verticalBuffer - margins.top; margins = shiftMarginsForPageBounds(margins, metrics); return getTileAlignedDisplayPortMetrics(margins, metrics.zoomFactor, metrics); } @Override public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) { // Increase the size of the viewport based on the danger zone multiplier (and clamp to page // boundaries), and intersect it with the current displayport to determine whether we're // close to checkerboarding. RectF adjustedViewport = expandByDangerZone(metrics.getViewport(), DANGER_ZONE_X_MULTIPLIER, DANGER_ZONE_Y_MULTIPLIER, metrics); return !displayPort.contains(adjustedViewport); } @Override public String toString() { return "FixedMarginStrategy mult=" + SIZE_MULTIPLIER + ", dangerX=" + DANGER_ZONE_X_MULTIPLIER + ", dangerY=" + DANGER_ZONE_Y_MULTIPLIER; } } /** * This class implements the variation with a small fixed-size margin with velocity bias. * In this variation, the default margins are pretty small relative to the view size, but * they are affected by the panning velocity. Specifically, if we are panning on one axis, * we remove the margins on the other axis because we are likely axis-locked. Also once * we are panning in one direction above a certain threshold velocity, we shift the buffer * so that it is almost entirely in the direction of the pan, with a little bit in the * reverse direction. */ private static class VelocityBiasStrategy extends DisplayPortStrategy { // The length of each axis of the display port will be the corresponding view length // multiplied by this factor. private final float SIZE_MULTIPLIER; // The velocity above which we apply the velocity bias private final float VELOCITY_THRESHOLD; // How much of the buffer to keep in the reverse direction of the velocity private final float REVERSE_BUFFER; // If the visible rect is within the danger zone we start redrawing to minimize // checkerboarding. the danger zone amount is a linear function of the form: // viewportsize * (base + velocity * incr) // where base and incr are configurable values. private final float DANGER_ZONE_BASE_X_MULTIPLIER; private final float DANGER_ZONE_BASE_Y_MULTIPLIER; private final float DANGER_ZONE_INCR_X_MULTIPLIER; private final float DANGER_ZONE_INCR_Y_MULTIPLIER; VelocityBiasStrategy(Map prefs) { SIZE_MULTIPLIER = getFloatPref(prefs, PREF_DISPLAYPORT_VB_MULTIPLIER, 2000); VELOCITY_THRESHOLD = GeckoAppShell.getDpi() * getFloatPref(prefs, PREF_DISPLAYPORT_VB_VELOCITY_THRESHOLD, 32); REVERSE_BUFFER = getFloatPref(prefs, PREF_DISPLAYPORT_VB_REVERSE_BUFFER, 200); DANGER_ZONE_BASE_X_MULTIPLIER = getFloatPref(prefs, PREF_DISPLAYPORT_VB_DANGER_X_BASE, 1000); DANGER_ZONE_BASE_Y_MULTIPLIER = getFloatPref(prefs, PREF_DISPLAYPORT_VB_DANGER_Y_BASE, 1000); DANGER_ZONE_INCR_X_MULTIPLIER = getFloatPref(prefs, PREF_DISPLAYPORT_VB_DANGER_X_INCR, 0); DANGER_ZONE_INCR_Y_MULTIPLIER = getFloatPref(prefs, PREF_DISPLAYPORT_VB_DANGER_Y_INCR, 0); } /** * Split the given amounts into margins based on the VELOCITY_THRESHOLD and REVERSE_BUFFER values. * If the velocity is above the VELOCITY_THRESHOLD on an axis, split the amount into REVERSE_BUFFER * and 1.0 - REVERSE_BUFFER fractions. The REVERSE_BUFFER fraction is set as the margin in the * direction opposite to the velocity, and the remaining fraction is set as the margin in the direction * of the velocity. If the velocity is lower than VELOCITY_THRESHOLD, split the amount evenly into the * two margins on that axis. */ private RectF velocityBiasedMargins(float xAmount, float yAmount, PointF velocity) { RectF margins = new RectF(); if (velocity.x > VELOCITY_THRESHOLD) { margins.left = xAmount * REVERSE_BUFFER; } else if (velocity.x < -VELOCITY_THRESHOLD) { margins.left = xAmount * (1.0f - REVERSE_BUFFER); } else { margins.left = xAmount / 2.0f; } margins.right = xAmount - margins.left; if (velocity.y > VELOCITY_THRESHOLD) { margins.top = yAmount * REVERSE_BUFFER; } else if (velocity.y < -VELOCITY_THRESHOLD) { margins.top = yAmount * (1.0f - REVERSE_BUFFER); } else { margins.top = yAmount / 2.0f; } margins.bottom = yAmount - margins.top; return margins; } @Override public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) { float displayPortWidth = metrics.getWidth() * SIZE_MULTIPLIER; float displayPortHeight = metrics.getHeight() * SIZE_MULTIPLIER; // but if we're panning on one axis, set the margins for the other axis to zero since we are likely // axis locked and won't be displaying that extra area. if (Math.abs(velocity.x) > VELOCITY_THRESHOLD && FloatUtils.fuzzyEquals(velocity.y, 0)) { displayPortHeight = metrics.getHeight(); } else if (Math.abs(velocity.y) > VELOCITY_THRESHOLD && FloatUtils.fuzzyEquals(velocity.x, 0)) { displayPortWidth = metrics.getWidth(); } // we need to avoid having a display port that is larger than the page, or we will end up // painting things outside the page bounds (bug 729169). displayPortWidth = Math.min(displayPortWidth, metrics.getPageWidth()); displayPortHeight = Math.min(displayPortHeight, metrics.getPageHeight()); float horizontalBuffer = displayPortWidth - metrics.getWidth(); float verticalBuffer = displayPortHeight - metrics.getHeight(); // split the buffer amounts into margins based on velocity, and shift it to // take into account the page bounds RectF margins = velocityBiasedMargins(horizontalBuffer, verticalBuffer, velocity); margins = shiftMarginsForPageBounds(margins, metrics); return getTileAlignedDisplayPortMetrics(margins, metrics.zoomFactor, metrics); } @Override public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) { // calculate the danger zone amounts based on the prefs float dangerZoneX = metrics.getWidth() * (DANGER_ZONE_BASE_X_MULTIPLIER + (velocity.x * DANGER_ZONE_INCR_X_MULTIPLIER)); float dangerZoneY = metrics.getHeight() * (DANGER_ZONE_BASE_Y_MULTIPLIER + (velocity.y * DANGER_ZONE_INCR_Y_MULTIPLIER)); // clamp it such that when added to the viewport, they don't exceed page size. // this is a prerequisite to calling shiftMarginsForPageBounds as we do below. dangerZoneX = Math.min(dangerZoneX, metrics.getPageWidth() - metrics.getWidth()); dangerZoneY = Math.min(dangerZoneY, metrics.getPageHeight() - metrics.getHeight()); // split the danger zone into margins based on velocity, and ensure it doesn't exceed // page bounds. RectF dangerMargins = velocityBiasedMargins(dangerZoneX, dangerZoneY, velocity); dangerMargins = shiftMarginsForPageBounds(dangerMargins, metrics); // we're about to checkerboard if the current viewport area + the danger zone margins // fall out of the current displayport anywhere. RectF adjustedViewport = new RectF( metrics.viewportRectLeft - dangerMargins.left, metrics.viewportRectTop - dangerMargins.top, metrics.viewportRectRight + dangerMargins.right, metrics.viewportRectBottom + dangerMargins.bottom); return !displayPort.contains(adjustedViewport); } @Override public String toString() { return "VelocityBiasStrategy mult=" + SIZE_MULTIPLIER + ", threshold=" + VELOCITY_THRESHOLD + ", reverse=" + REVERSE_BUFFER + ", dangerBaseX=" + DANGER_ZONE_BASE_X_MULTIPLIER + ", dangerBaseY=" + DANGER_ZONE_BASE_Y_MULTIPLIER + ", dangerIncrX=" + DANGER_ZONE_INCR_Y_MULTIPLIER + ", dangerIncrY=" + DANGER_ZONE_INCR_Y_MULTIPLIER; } } /** * This class implements the variation where we draw more of the page at low resolution while panning. * In this variation, as we pan faster, we increase the page area we are drawing, but reduce the draw * resolution to compensate. This results in the same device-pixel area drawn; the compositor then * scales this up to the viewport zoom level. This results in a large area of the page drawn but it * looks blurry. The assumption is that drawing extra that we never display is better than checkerboarding, * where we draw less but never even show it on the screen. */ private static class DynamicResolutionStrategy extends DisplayPortStrategy { // The length of each axis of the display port will be the corresponding view length // multiplied by this factor. private static final float SIZE_MULTIPLIER = 1.5f; // The velocity above which we start zooming out the display port to keep up // with the panning. private static final float VELOCITY_EXPANSION_THRESHOLD = GeckoAppShell.getDpi() / 16f; // How much we increase the display port based on velocity. Assuming no friction and // splitting (see below), this should be be the number of frames (@60fps) between us // calculating the display port and the draw of the *next* display port getting composited // and displayed on the screen. This is because the timeline looks like this: // Java: pan pan pan pan pan pan ! pan pan pan pan pan pan ! // Gecko: \-> draw -> composite / \-> draw -> composite / // The display port calculated on the first "pan" gets composited to the screen at the // first exclamation mark, and remains on the screen until the second exclamation mark. // In order to avoid checkerboarding, that display port must be able to contain all of // the panning until the second exclamation mark, which encompasses two entire draw/composite // cycles. // If we take into account friction, our velocity multiplier should be reduced as the // amount of pan will decrease each time. If we take into account display port splitting, // it should be increased as the splitting means some of the display port will be used to // draw in the opposite direction of the velocity. For now I'm assuming these two cancel // each other out. private static final float VELOCITY_MULTIPLIER = 60.0f; // The following constants adjust how biased the display port is in the direction of panning. // When panning fast (above the FAST_THRESHOLD) we use the fast split factor to split the // display port "buffer" area, otherwise we use the slow split factor. This is based on the // assumption that if the user is panning fast, they are less likely to reverse directions // and go backwards, so we should spend more of our display port buffer in the direction of // panning. private static final float VELOCITY_FAST_THRESHOLD = VELOCITY_EXPANSION_THRESHOLD * 2.0f; private static final float FAST_SPLIT_FACTOR = 0.95f; private static final float SLOW_SPLIT_FACTOR = 0.8f; // The following constants are used for viewport prediction; we use them to estimate where // the viewport will be soon and whether or not we should trigger a draw right now. "soon" // in the previous sentence really refers to the amount of time it would take to draw and // composite from the point at which we do the calculation, and that is not really a known // quantity. The velocity multiplier is how much we multiply the velocity by; it has the // same caveats as the VELOCITY_MULTIPLIER above except that it only needs to take into account // one draw/composite cycle instead of two. The danger zone multiplier is a multiplier of the // viewport size that we use as an extra "danger zone" around the viewport; if this danger // zone falls outside the display port then we are approaching the point at which we will // checkerboard, and hence should start drawing. Note that if DANGER_ZONE_MULTIPLIER is // greater than (SIZE_MULTIPLIER - 1.0f), then at zero velocity we will always be in the // danger zone, and thus will be constantly drawing. private static final float PREDICTION_VELOCITY_MULTIPLIER = 30.0f; private static final float DANGER_ZONE_MULTIPLIER = 0.20f; // must be less than (SIZE_MULTIPLIER - 1.0f) DynamicResolutionStrategy(Map prefs) { // ignore prefs for now } @Override public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) { float displayPortWidth = metrics.getWidth() * SIZE_MULTIPLIER; float displayPortHeight = metrics.getHeight() * SIZE_MULTIPLIER; // for resolution calculation purposes, we need to know what the adjusted display port dimensions // would be if we had zero velocity, so calculate that here before we increase the display port // based on velocity. FloatSize reshapedSize = reshapeForPage(displayPortWidth, displayPortHeight, metrics); // increase displayPortWidth and displayPortHeight based on the velocity, but maintaining their // relative aspect ratio. if (velocity.length() > VELOCITY_EXPANSION_THRESHOLD) { float velocityFactor = Math.max(Math.abs(velocity.x) / displayPortWidth, Math.abs(velocity.y) / displayPortHeight); velocityFactor *= VELOCITY_MULTIPLIER; displayPortWidth += (displayPortWidth * velocityFactor); displayPortHeight += (displayPortHeight * velocityFactor); } // at this point, displayPortWidth and displayPortHeight are how much of the page (in device pixels) // we want to be rendered by Gecko. Note here "device pixels" is equivalent to CSS pixels multiplied // by metrics.zoomFactor // we need to avoid having a display port that is larger than the page, or we will end up // painting things outside the page bounds (bug 729169). we simultaneously need to make // the display port as large as possible so that we redraw less. reshape the display // port dimensions to accomplish this. this may change the aspect ratio of the display port, // but we are assuming that this is desirable because the advantages from pre-drawing will // outweigh the disadvantages from any buffer reallocations that might occur. FloatSize usableSize = reshapeForPage(displayPortWidth, displayPortHeight, metrics); float horizontalBuffer = usableSize.width - metrics.getWidth(); float verticalBuffer = usableSize.height - metrics.getHeight(); // at this point, horizontalBuffer and verticalBuffer are the dimensions of the buffer area we have. // the buffer area is the off-screen area that is part of the display port and will be pre-drawn in case // the user scrolls there. we now need to split the buffer area on each axis so that we know // what the exact margins on each side will be. first we split the buffer amount based on the direction // we're moving, so that we have a larger buffer in the direction of travel. RectF margins = new RectF(); margins.left = splitBufferByVelocity(horizontalBuffer, velocity.x); margins.right = horizontalBuffer - margins.left; margins.top = splitBufferByVelocity(verticalBuffer, velocity.y); margins.bottom = verticalBuffer - margins.top; // 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); } } @Override 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); } @Override public String toString() { return "DynamicResolutionStrategy"; } } /** * This class implements the variation where we use the draw time to predict where we will be when * a draw completes, and draw that instead of where we are now. In this variation, when our panning * speed drops below a certain threshold, we draw 9 viewports' worth of content so that the user can * pan in any direction without encountering checkerboarding. * Once the user is panning, we modify the displayport to encompass an area range of where we think * the user will be when the draw completes. This heuristic relies on both the estimated draw time * the panning velocity; unexpected changes in either of these values will cause the heuristic to * fail and show checkerboard. */ private static class PredictionBiasStrategy extends DisplayPortStrategy { private static float VELOCITY_THRESHOLD; private int mPixelArea; // area of the viewport, used in draw time calculations private int mMinFramesToDraw; // minimum number of frames we take to draw private int mMaxFramesToDraw; // maximum number of frames we take to draw PredictionBiasStrategy(Map prefs) { VELOCITY_THRESHOLD = GeckoAppShell.getDpi() * getFloatPref(prefs, PREF_DISPLAYPORT_PB_VELOCITY_THRESHOLD, 16); resetPageState(); } @Override public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) { float width = metrics.getWidth(); float height = metrics.getHeight(); mPixelArea = (int)(width * height); if (velocity.length() < VELOCITY_THRESHOLD) { // if we're going slow, expand the displayport to 9x viewport size RectF margins = new RectF(width, height, width, height); return getTileAlignedDisplayPortMetrics(margins, metrics.zoomFactor, metrics); } // figure out how far we expect to be float minDx = velocity.x * mMinFramesToDraw; float minDy = velocity.y * mMinFramesToDraw; float maxDx = velocity.x * mMaxFramesToDraw; float maxDy = velocity.y * mMaxFramesToDraw; // figure out how many pixels we will be drawing when we draw the above-calculated range. // this will be larger than the viewport area. float pixelsToDraw = (width + Math.abs(maxDx - minDx)) * (height + Math.abs(maxDy - minDy)); // adjust how far we will get because of the time spent drawing all these extra pixels. this // will again increase the number of pixels drawn so really we could keep iterating this over // and over, but once seems enough for now. maxDx = maxDx * pixelsToDraw / mPixelArea; maxDy = maxDy * pixelsToDraw / mPixelArea; // and finally generate the displayport. the min/max stuff takes care of // negative velocities as well as positive. RectF margins = new RectF( -Math.min(minDx, maxDx), -Math.min(minDy, maxDy), Math.max(minDx, maxDx), Math.max(minDy, maxDy)); return getTileAlignedDisplayPortMetrics(margins, metrics.zoomFactor, metrics); } @Override public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) { // the code below is the same as in calculate() but is awkward to refactor since it has multiple outputs. // refer to the comments in calculate() to understand what this is doing. float minDx = velocity.x * mMinFramesToDraw; float minDy = velocity.y * mMinFramesToDraw; float maxDx = velocity.x * mMaxFramesToDraw; float maxDy = velocity.y * mMaxFramesToDraw; float pixelsToDraw = (metrics.getWidth() + Math.abs(maxDx - minDx)) * (metrics.getHeight() + Math.abs(maxDy - minDy)); maxDx = maxDx * pixelsToDraw / mPixelArea; maxDy = maxDy * pixelsToDraw / mPixelArea; // now that we have an idea of how far we will be when the draw completes, take the farthest // end of that range and see if it falls outside the displayport bounds. if it does, allow // the draw to go through RectF predictedViewport = metrics.getViewport(); predictedViewport.left += maxDx; predictedViewport.top += maxDy; predictedViewport.right += maxDx; predictedViewport.bottom += maxDy; predictedViewport = clampToPageBounds(predictedViewport, metrics); return !displayPort.contains(predictedViewport); } @Override public boolean drawTimeUpdate(long millis, int pixels) { // calculate the number of frames it took to draw a viewport-sized area float normalizedTime = (float)mPixelArea * (float)millis / (float)pixels; int normalizedFrames = (int)FloatMath.ceil(normalizedTime * 60f / 1000f); // broaden our range on how long it takes to draw if the draw falls outside // the range. this allows it to grow gradually. this heuristic may need to // be tweaked into more of a floating window average or something. if (normalizedFrames <= mMinFramesToDraw) { mMinFramesToDraw--; } else if (normalizedFrames > mMaxFramesToDraw) { mMaxFramesToDraw++; } else { return true; } Log.d(LOGTAG, "Widened draw range to [" + mMinFramesToDraw + ", " + mMaxFramesToDraw + "]"); return true; } @Override public void resetPageState() { mMinFramesToDraw = 0; mMaxFramesToDraw = 2; } @Override public String toString() { return "PredictionBiasStrategy threshold=" + VELOCITY_THRESHOLD; } } }