1 /*
2  * Copyright (C) 2014 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 
18 package com.android.internal.widget;
19 
20 import android.graphics.Canvas;
21 import android.graphics.PixelFormat;
22 import android.graphics.drawable.Drawable;
23 import android.view.View;
24 import android.view.ViewGroup;
25 
26 /**
27  * Helper class for drawing a fallback background in framework decor layouts.
28  * Useful for when an app has not set a window background but we're asked to draw
29  * an uncovered area.
30  */
31 public class BackgroundFallback {
32     private Drawable mBackgroundFallback;
33 
setDrawable(Drawable d)34     public void setDrawable(Drawable d) {
35         mBackgroundFallback = d;
36     }
37 
hasFallback()38     public boolean hasFallback() {
39         return mBackgroundFallback != null;
40     }
41 
42     /**
43      * Draws the fallback background.
44      *
45      * @param boundsView The view determining with which bounds the background should be drawn.
46      * @param root The view group containing the content.
47      * @param c The canvas to draw the background onto.
48      * @param content The view where the actual app content is contained in.
49      * @param coveringView1 A potentially opaque view drawn atop the content
50      * @param coveringView2 A potentially opaque view drawn atop the content
51      */
draw(ViewGroup boundsView, ViewGroup root, Canvas c, View content, View coveringView1, View coveringView2)52     public void draw(ViewGroup boundsView, ViewGroup root, Canvas c, View content,
53             View coveringView1, View coveringView2) {
54         if (!hasFallback()) {
55             return;
56         }
57 
58         // Draw the fallback in the padding.
59         final int width = boundsView.getWidth();
60         final int height = boundsView.getHeight();
61 
62         final int rootOffsetX = root.getLeft();
63         final int rootOffsetY = root.getTop();
64 
65         int left = width;
66         int top = height;
67         int right = 0;
68         int bottom = 0;
69 
70         final int childCount = root.getChildCount();
71         for (int i = 0; i < childCount; i++) {
72             final View child = root.getChildAt(i);
73             final Drawable childBg = child.getBackground();
74             if (child == content) {
75                 // We always count the content view container unless it has no background
76                 // and no children.
77                 if (childBg == null && child instanceof ViewGroup &&
78                         ((ViewGroup) child).getChildCount() == 0) {
79                     continue;
80                 }
81             } else if (child.getVisibility() != View.VISIBLE || !isOpaque(childBg)) {
82                 // Potentially translucent or invisible children don't count, and we assume
83                 // the content view will cover the whole area if we're in a background
84                 // fallback situation.
85                 continue;
86             }
87             left = Math.min(left, rootOffsetX + child.getLeft());
88             top = Math.min(top, rootOffsetY + child.getTop());
89             right = Math.max(right, rootOffsetX + child.getRight());
90             bottom = Math.max(bottom, rootOffsetY + child.getBottom());
91         }
92 
93         // If one of the bar backgrounds is a solid color and covers the entire padding on a side
94         // we can drop that padding.
95         boolean eachBarCoversTopInY = true;
96         for (int i = 0; i < 2; i++) {
97             View v = (i == 0) ? coveringView1 : coveringView2;
98             if (v == null || v.getVisibility() != View.VISIBLE
99                     || v.getAlpha() != 1f || !isOpaque(v.getBackground())) {
100                 eachBarCoversTopInY = false;
101                 continue;
102             }
103 
104             // Bar covers entire left padding
105             if (v.getTop() <= 0 && v.getBottom() >= height
106                     && v.getLeft() <= 0 && v.getRight() >= left) {
107                 left = 0;
108             }
109             // Bar covers entire right padding
110             if (v.getTop() <= 0 && v.getBottom() >= height
111                     && v.getLeft() <= right && v.getRight() >= width) {
112                 right = width;
113             }
114             // Bar covers entire top padding
115             if (v.getTop() <= 0 && v.getBottom() >= top
116                     && v.getLeft() <= 0 && v.getRight() >= width) {
117                 top = 0;
118             }
119             // Bar covers entire bottom padding
120             if (v.getTop() <= bottom && v.getBottom() >= height
121                     && v.getLeft() <= 0 && v.getRight() >= width) {
122                 bottom = height;
123             }
124 
125             eachBarCoversTopInY &= v.getTop() <= 0 && v.getBottom() >= top;
126         }
127 
128         // Special case: Sometimes, both covering views together may cover the top inset, but
129         // neither does on its own.
130         if (eachBarCoversTopInY && (viewsCoverEntireWidth(coveringView1, coveringView2, width)
131                 || viewsCoverEntireWidth(coveringView2, coveringView1, width))) {
132             top = 0;
133         }
134 
135         if (left >= right || top >= bottom) {
136             // No valid area to draw in.
137             return;
138         }
139 
140         if (top > 0) {
141             mBackgroundFallback.setBounds(0, 0, width, top);
142             mBackgroundFallback.draw(c);
143         }
144         if (left > 0) {
145             mBackgroundFallback.setBounds(0, top, left, height);
146             mBackgroundFallback.draw(c);
147         }
148         if (right < width) {
149             mBackgroundFallback.setBounds(right, top, width, height);
150             mBackgroundFallback.draw(c);
151         }
152         if (bottom < height) {
153             mBackgroundFallback.setBounds(left, bottom, right, height);
154             mBackgroundFallback.draw(c);
155         }
156     }
157 
isOpaque(Drawable childBg)158     private boolean isOpaque(Drawable childBg) {
159         return childBg != null && childBg.getOpacity() == PixelFormat.OPAQUE;
160     }
161 
162     /**
163      * Returns true if {@code view1} starts before or on {@code 0} and extends at least
164      * up to {@code view2}, and that view extends at least to {@code width}.
165      *
166      * @param view1 the first view to check if it covers the width
167      * @param view2 the second view to check if it covers the width
168      * @param width the width to check for
169      * @return returns true if both views together cover the entire width (and view1 is to the left
170      *         of view2)
171      */
viewsCoverEntireWidth(View view1, View view2, int width)172     private boolean viewsCoverEntireWidth(View view1, View view2, int width) {
173         return view1.getLeft() <= 0
174                 && view1.getRight() >= view2.getLeft()
175                 && view2.getRight() >= width;
176     }
177 }
178