1/*
2 * Copyright (C) 2015 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
17package android.view;
18
19import com.android.layoutlib.bridge.impl.ResourceHelper;
20
21import android.graphics.Canvas;
22import android.graphics.Canvas_Delegate;
23import android.graphics.LinearGradient;
24import android.graphics.Outline;
25import android.graphics.Paint;
26import android.graphics.Paint.Style;
27import android.graphics.Path;
28import android.graphics.Path.FillType;
29import android.graphics.RadialGradient;
30import android.graphics.Rect;
31import android.graphics.RectF;
32import android.graphics.Region.Op;
33import android.graphics.Shader.TileMode;
34
35/**
36 * Paints shadow for rounded rectangles. Inspiration from CardView. Couldn't use that directly,
37 * since it modifies the size of the content, that we can't do.
38 */
39public class RectShadowPainter {
40
41
42    private static final int START_COLOR = ResourceHelper.getColor("#37000000");
43    private static final int END_COLOR = ResourceHelper.getColor("#03000000");
44    private static final float PERPENDICULAR_ANGLE = 90f;
45
46    public static void paintShadow(Outline viewOutline, float elevation, Canvas canvas) {
47        Rect outline = new Rect();
48        if (!viewOutline.getRect(outline)) {
49            throw new IllegalArgumentException("Outline is not a rect shadow");
50        }
51
52        float shadowSize = elevationToShadow(elevation);
53        int saved = modifyCanvas(canvas, shadowSize);
54        if (saved == -1) {
55            return;
56        }
57        try {
58            Paint cornerPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);
59            cornerPaint.setStyle(Style.FILL);
60            Paint edgePaint = new Paint(cornerPaint);
61            edgePaint.setAntiAlias(false);
62            float radius = viewOutline.getRadius();
63            float outerArcRadius = radius + shadowSize;
64            int[] colors = {START_COLOR, START_COLOR, END_COLOR};
65            cornerPaint.setShader(new RadialGradient(0, 0, outerArcRadius, colors,
66                    new float[]{0f, radius / outerArcRadius, 1f}, TileMode.CLAMP));
67            edgePaint.setShader(new LinearGradient(0, 0, -shadowSize, 0, START_COLOR, END_COLOR,
68                    TileMode.CLAMP));
69            Path path = new Path();
70            path.setFillType(FillType.EVEN_ODD);
71            // A rectangle bounding the complete shadow.
72            RectF shadowRect = new RectF(outline);
73            shadowRect.inset(-shadowSize, -shadowSize);
74            // A rectangle with edges corresponding to the straight edges of the outline.
75            RectF inset = new RectF(outline);
76            inset.inset(radius, radius);
77            // A rectangle used to represent the edge shadow.
78            RectF edgeShadowRect = new RectF();
79
80
81            // left and right sides.
82            edgeShadowRect.set(-shadowSize, 0f, 0f, inset.height());
83            // Left shadow
84            sideShadow(canvas, edgePaint, edgeShadowRect, outline.left, inset.top, 0);
85            // Right shadow
86            sideShadow(canvas, edgePaint, edgeShadowRect, outline.right, inset.bottom, 2);
87            // Top shadow
88            edgeShadowRect.set(-shadowSize, 0, 0, inset.width());
89            sideShadow(canvas, edgePaint, edgeShadowRect, inset.right, outline.top, 1);
90            // bottom shadow. This needs an inset so that blank doesn't appear when the content is
91            // moved up.
92            edgeShadowRect.set(-shadowSize, 0, shadowSize / 2f, inset.width());
93            edgePaint.setShader(new LinearGradient(edgeShadowRect.right, 0, edgeShadowRect.left, 0,
94                    colors, new float[]{0f, 1 / 3f, 1f}, TileMode.CLAMP));
95            sideShadow(canvas, edgePaint, edgeShadowRect, inset.left, outline.bottom, 3);
96
97            // Draw corners.
98            drawCorner(canvas, cornerPaint, path, inset.right, inset.bottom, outerArcRadius, 0);
99            drawCorner(canvas, cornerPaint, path, inset.left, inset.bottom, outerArcRadius, 1);
100            drawCorner(canvas, cornerPaint, path, inset.left, inset.top, outerArcRadius, 2);
101            drawCorner(canvas, cornerPaint, path, inset.right, inset.top, outerArcRadius, 3);
102        } finally {
103            canvas.restoreToCount(saved);
104        }
105    }
106
107    private static float elevationToShadow(float elevation) {
108        // The factor is chosen by eyeballing the shadow size on device and preview.
109        return elevation * 0.5f;
110    }
111
112    /**
113     * Translate canvas by half of shadow size up, so that it appears that light is coming
114     * slightly from above. Also, remove clipping, so that shadow is not clipped.
115     */
116    private static int modifyCanvas(Canvas canvas, float shadowSize) {
117        Rect clipBounds = canvas.getClipBounds();
118        if (clipBounds.isEmpty()) {
119            return -1;
120        }
121        int saved = canvas.save();
122        // Usually canvas has been translated to the top left corner of the view when this is
123        // called. So, setting a clip rect at 0,0 will clip the top left part of the shadow.
124        // Thus, we just expand in each direction by width and height of the canvas.
125        canvas.clipRect(-canvas.getWidth(), -canvas.getHeight(), canvas.getWidth(),
126                canvas.getHeight(), Op.REPLACE);
127        canvas.translate(0, shadowSize / 2f);
128        return saved;
129    }
130
131    private static void sideShadow(Canvas canvas, Paint edgePaint,
132            RectF edgeShadowRect, float dx, float dy, int rotations) {
133        if (isRectEmpty(edgeShadowRect)) {
134            return;
135        }
136        int saved = canvas.save();
137        canvas.translate(dx, dy);
138        canvas.rotate(rotations * PERPENDICULAR_ANGLE);
139        canvas.drawRect(edgeShadowRect, edgePaint);
140        canvas.restoreToCount(saved);
141    }
142
143    /**
144     * @param canvas Canvas to draw the rectangle on.
145     * @param paint Paint to use when drawing the corner.
146     * @param path A path to reuse. Prevents allocating memory for each path.
147     * @param x Center of circle, which this corner is a part of.
148     * @param y Center of circle, which this corner is a part of.
149     * @param radius radius of the arc
150     * @param rotations number of quarter rotations before starting to paint the arc.
151     */
152    private static void drawCorner(Canvas canvas, Paint paint, Path path, float x, float y,
153            float radius, int rotations) {
154        int saved = canvas.save();
155        canvas.translate(x, y);
156        path.reset();
157        path.arcTo(-radius, -radius, radius, radius, rotations * PERPENDICULAR_ANGLE,
158                PERPENDICULAR_ANGLE, false);
159        path.lineTo(0, 0);
160        path.close();
161        canvas.drawPath(path, paint);
162        canvas.restoreToCount(saved);
163    }
164
165    /**
166     * Differs from {@link RectF#isEmpty()} as this first converts the rect to int and then checks.
167     * <p/>
168     * This is required because {@link Canvas_Delegate#native_drawRect(long, float, float, float,
169     * float, long)} casts the co-ordinates to int and we want to ensure that it doesn't end up
170     * drawing empty rectangles, which results in IllegalArgumentException.
171     */
172    private static boolean isRectEmpty(RectF rect) {
173        return (int) rect.left >= (int) rect.right || (int) rect.top >= (int) rect.bottom;
174    }
175}
176