Add display preference for scaling / UI Zoom feature

Bug: 22450672
Change-Id: If665576869743fd7d5fc23103260eecaa366e7aa

res/values/strings.xml

@@ -6978,4 +6978,22 @@
 
     <!-- Description of feature to change color setting for the display [CHAR LIMIT=NONE] -->
     <string name="picture_color_mode_desc">Use sRGB</string>
+
+    <!-- Title of setting that controls display scale (e.g. density). [CHAR LIMIT=40] -->
+    <string name="force_density_preference_title">Display scale</string>
+    <!-- Keywords for setting that controls display scale (e.g. density). [CHAR LIMIT=NONE] -->
+    <string name="force_density_keywords">display density zoom scale scaling</string>
+    <!-- Description for the display scale that makes interface elements small. [CHAR LIMIT=24] -->
+    <string name="force_density_summary_small">Small</string>
+    <!-- Description for the device's default display scale. [CHAR LIMIT=24] -->
+    <string name="force_density_summary_normal">Normal</string>
+    <!-- Description for the display scale that makes interface elements large. [CHAR LIMIT=24] -->
+    <string name="force_density_summary_large">Large</string>
+    <!-- Description for the display scale that makes interface elements larger. [CHAR LIMIT=24] -->
+    <string name="force_density_summary_very_large">Larger</string>
+    <!-- Description for the display scale that makes interface elements largest. [CHAR LIMIT=24] -->
+    <string name="force_density_summary_extremely_large">Largest</string>
+    <!-- Description for a custom display scale. This shows the requested display
+         density in raw pixels per inch rather than computing a scale amount. [CHAR LIMIT=24] -->
+    <string name="force_density_summary_custom">Custom (<xliff:g id="densityDpi" example="160">%d</xliff:g>)</string>
 </resources>

res/xml/display_settings.xml

@@ -99,6 +99,13 @@
                 android:entries="@array/entries_font_size"
                 android:entryValues="@array/entryvalues_font_size" />
 
+        <com.android.settings.DisplayDensityPreference
+                android:key="display_density"
+                android:title="@string/force_density_preference_title"
+                android:summary="%s"
+                settings:keywords="@string/force_density_keywords"
+                android:persistent="false" />
+
         <com.android.settings.DropDownPreference
                 android:key="auto_rotate"
                 android:title="@string/display_auto_rotate_title" />

src/com/android/settings/DisplayDensityPreference.java

@@ -0,0 +1,247 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+package com.android.settings;
+
+import android.content.Context;
+import android.content.res.Resources;
+import android.os.AsyncTask;
+import android.os.RemoteException;
+import android.support.annotation.ArrayRes;
+import android.support.v7.preference.ListPreference;
+import android.util.AttributeSet;
+import android.util.DisplayMetrics;
+import android.util.Log;
+import android.util.MathUtils;
+import android.view.Display;
+import android.view.IWindowManager;
+import android.view.WindowManagerGlobal;
+
+import com.android.settings.R;
+
+import java.util.Arrays;
+
+/**
+ * Preference for changing the density of the display on which the preference
+ * is visible.
+ */
+public class DisplayDensityPreference extends ListPreference {
+    private static final String LOG_TAG = "DisplayDensityPreference";
+
+    /** Minimum increment between density scales. */
+    private static final float MIN_SCALE_INTERVAL = 0.09f;
+
+    /** Minimum density scale. This is available on all devices. */
+    private static final float MIN_SCALE = 0.85f;
+
+    /** Maximum density scale. The actual scale used depends on the device. */
+    private static final float MAX_SCALE = 1.50f;
+
+    /** Sentinel value for "normal" scaling (effectively disabled). */
+    private static final int DENSITY_VALUE_NORMAL = -1;
+
+    /** Summary used for "normal" scale. */
+    private static final int DENSITY_SUMMARY_NORMAL = R.string.force_density_summary_normal;
+
+    /**
+     * Summaries for scales smaller than "normal" in order of smallest to
+     * largest.
+     */
+    private static final int[] SMALLER_SUMMARIES = new int[] {
+            R.string.force_density_summary_small
+    };
+
+    /**
+     * Summaries for scales larger than "normal" in order of smallest to
+     * largest.
+     */
+    private static final int[] LARGER_SUMMARIES = new int[] {
+            R.string.force_density_summary_large,
+            R.string.force_density_summary_very_large,
+            R.string.force_density_summary_extremely_large,
+    };
+
+    /**
+     * Minimum allowed screen dimension, corresponds to resource qualifiers
+     * "small" or "sw320dp". This value must be at least the minimum screen
+     * size required by the CDD so that we meet developer expectations.
+     */
+    private static final int MIN_DIMENSION_DP = 320;
+
+    /** The ID of the display affected by this preference. */
+    private int mDisplayId = Display.DEFAULT_DISPLAY;
+
+    public DisplayDensityPreference(Context context, AttributeSet attrs) {
+        super(context, attrs);
+
+        if (!prepareList()) {
+            setEnabled(false);
+        }
+    }
+
+    private boolean prepareList() {
+        final int initialDensity = getInitialDisplayDensity(mDisplayId);
+        if (initialDensity <= 0) {
+            return false;
+        }
+
+        final Resources res = getContext().getResources();
+        final DisplayMetrics metrics = res.getDisplayMetrics();
+        final int currentDensity = metrics.densityDpi;
+        int currentDensityIndex = -1;
+
+        // Compute number of "larger" and "smaller" scales for this display.
+        final int minDimensionPx = Math.min(metrics.widthPixels, metrics.heightPixels);
+        final int maxDensity = DisplayMetrics.DENSITY_MEDIUM * minDimensionPx / MIN_DIMENSION_DP;
+        final float maxScale = Math.min(MAX_SCALE, maxDensity / (float) initialDensity);
+        final float minScale = MIN_SCALE;
+        final int numLarger = (int) MathUtils.constrain((maxScale - 1) / MIN_SCALE_INTERVAL,
+                0, LARGER_SUMMARIES.length);
+        final int numSmaller = (int) MathUtils.constrain((1 - minScale) / MIN_SCALE_INTERVAL,
+                0, SMALLER_SUMMARIES.length);
+
+        CharSequence[] values = new CharSequence[1 + numSmaller + numLarger];
+        CharSequence[] entries = new CharSequence[values.length];
+        int curIndex = 0;
+
+        if (numSmaller > 0) {
+            final float interval = (1 - minScale) / numSmaller;
+            for (int i = numSmaller - 1; i >= 0; i--) {
+                final int density = (int) (initialDensity * (1 - (i + 1) * interval));
+                if (currentDensity == density) {
+                    currentDensityIndex = curIndex;
+                }
+                values[curIndex] = Integer.toString(density);
+                entries[curIndex] = res.getText(SMALLER_SUMMARIES[i]);
+                curIndex++;
+            }
+        }
+
+        if (currentDensity == initialDensity) {
+            currentDensityIndex = curIndex;
+        }
+        values[curIndex] = Integer.toString(DENSITY_VALUE_NORMAL);
+        entries[curIndex] = res.getText(DENSITY_SUMMARY_NORMAL);
+        curIndex++;
+
+        if (numLarger > 0) {
+            final float interval = (maxScale - 1) / numLarger;
+            for (int i = 0; i < numLarger; i++) {
+                final int density = (int) (initialDensity * (1 + (i + 1) * interval));
+                if (currentDensity == density) {
+                    currentDensityIndex = curIndex;
+                }
+                values[curIndex] = Integer.toString(density);
+                entries[curIndex] = res.getText(LARGER_SUMMARIES[i]);
+                curIndex++;
+            }
+        }
+
+        final int displayIndex;
+        if (currentDensityIndex >= 0) {
+            displayIndex = currentDensityIndex;
+        } else {
+            // We don't understand the current density. Must have been set by
+            // someone else. Make room for another entry...
+            values = Arrays.copyOf(values, values.length + 1);
+            values[curIndex] = res.getString(R.string.force_density_summary_custom, currentDensity);
+
+            entries = Arrays.copyOf(entries, values.length + 1);
+            entries[curIndex] = Integer.toString(currentDensity);
+
+            displayIndex = curIndex;
+        }
+
+        super.setEntryValues(values);
+        super.setEntries(entries);
+
+        setValueIndex(displayIndex);
+
+        return true;
+    }
+
+    @Override
+    public boolean callChangeListener(Object newValue) {
+        final boolean allowed = super.callChangeListener(newValue);
+        if (allowed) {
+            final int density = Integer.parseInt((String) newValue);
+            setForcedDisplayDensity(mDisplayId, density);
+        }
+
+        return allowed;
+    }
+
+    @Override
+    public void setEntries(CharSequence[] entries) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void setEntries(@ArrayRes int entriesResId) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void setEntryValues(CharSequence[] entryValues) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void setEntryValues(@ArrayRes int entryValuesResId) {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Returns the initial density for the specified display.
+     *
+     * @param displayId the identifier of the display
+     * @return the initial density of the specified display, or {@code -1} if
+     *         the display does not exist or the density could not be obtained
+     */
+    private static int getInitialDisplayDensity(int displayId) {
+        try {
+            IWindowManager wm = WindowManagerGlobal.getWindowManagerService();
+            return wm.getInitialDisplayDensity(displayId);
+        } catch (RemoteException exc) {
+            return -1;
+        }
+    }
+
+    /**
+     * Asynchronously applies display density changes to the specified display.
+     *
+     * @param displayId the identifier of the display to modify
+     * @param density the density to force for the specified display, or <= 0
+     *                to clear any previously forced density
+     */
+    private static void setForcedDisplayDensity(final int displayId, final int density) {
+        AsyncTask.execute(new Runnable() {
+            @Override
+            public void run() {
+                try {
+                    IWindowManager wm = WindowManagerGlobal.getWindowManagerService();
+                    if (density <= 0) {
+                        wm.clearForcedDisplayDensity(displayId);
+                    } else {
+                        wm.setForcedDisplayDensity(displayId, density);
+                    }
+                } catch (RemoteException exc) {
+                    Log.w(LOG_TAG, "Unable to save forced display density setting");
+                }
+            }
+        });
+    }
+}

src/com/android/settings/DisplaySettings.java

@@ -76,6 +76,7 @@ public class DisplaySettings extends SettingsPreferenceFragment implements
     private static final String KEY_CAMERA_GESTURE = "camera_gesture";
     private static final String KEY_CAMERA_DOUBLE_TAP_POWER_GESTURE
             = "camera_double_tap_power_gesture";
+    private static final String KEY_DISPLAY_DENSITY = "display_density";
 
     private DropDownPreference mFontSizePref;
 
@@ -213,6 +214,9 @@ public class DisplaySettings extends SettingsPreferenceFragment implements
             mNightModePreference.setValue(String.valueOf(currentNightMode));
             mNightModePreference.setOnPreferenceChangeListener(this);
         }
+
+        final Preference displayDensity = findPreference(KEY_DISPLAY_DENSITY);
+        displayDensity.setOnPreferenceChangeListener(this);
     }
 
     private static boolean allowAllRotations(Context context) {