gecko/mobile/android/base/gfx/DisplayPortCalculator.java

768 lines
42 KiB
Java

/* -*- 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 = "GeckoDisplayPortCalculator";
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<String, Integer> mValues = new HashMap<String, Integer>();
@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<String, Integer> 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<String, Integer> 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<String, Integer> prefs) {
// no prefs in this strategy
}
public DisplayPortMetrics calculate(ImmutableViewportMetrics metrics, PointF velocity) {
return new DisplayPortMetrics(metrics.viewportRectLeft,
metrics.viewportRectTop,
metrics.viewportRectRight,
metrics.viewportRectBottom,
metrics.zoomFactor);
}
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<String, Integer> 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);
}
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);
}
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<String, Integer> 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;
}
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);
}
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<String, Integer> prefs) {
// ignore prefs for now
}
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);
}
}
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<String, Integer> prefs) {
VELOCITY_THRESHOLD = GeckoAppShell.getDpi() * getFloatPref(prefs, PREF_DISPLAYPORT_PB_VELOCITY_THRESHOLD, 16);
resetPageState();
}
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);
}
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;
}
}
}