/*
* 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 android.view;
import com.android.layoutlib.bridge.impl.ResourceHelper;
import android.graphics.Canvas;
import android.graphics.Canvas_Delegate;
import android.graphics.LinearGradient;
import android.graphics.Outline;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Path;
import android.graphics.Path.FillType;
import android.graphics.RadialGradient;
import android.graphics.Rect;
import android.graphics.RectF;
import android.graphics.Region.Op;
import android.graphics.Shader.TileMode;
/**
* Paints shadow for rounded rectangles. Inspiration from CardView. Couldn't use that directly,
* since it modifies the size of the content, that we can't do.
*/
public class RectShadowPainter {
private static final int START_COLOR = ResourceHelper.getColor("#37000000");
private static final int END_COLOR = ResourceHelper.getColor("#03000000");
private static final float PERPENDICULAR_ANGLE = 90f;
public static void paintShadow(Outline viewOutline, float elevation, Canvas canvas) {
Rect outline = new Rect();
if (!viewOutline.getRect(outline)) {
throw new IllegalArgumentException("Outline is not a rect shadow");
}
float shadowSize = elevationToShadow(elevation);
int saved = modifyCanvas(canvas, shadowSize);
if (saved == -1) {
return;
}
try {
Paint cornerPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);
cornerPaint.setStyle(Style.FILL);
Paint edgePaint = new Paint(cornerPaint);
edgePaint.setAntiAlias(false);
float radius = viewOutline.getRadius();
float outerArcRadius = radius + shadowSize;
int[] colors = {START_COLOR, START_COLOR, END_COLOR};
cornerPaint.setShader(new RadialGradient(0, 0, outerArcRadius, colors,
new float[]{0f, radius / outerArcRadius, 1f}, TileMode.CLAMP));
edgePaint.setShader(new LinearGradient(0, 0, -shadowSize, 0, START_COLOR, END_COLOR,
TileMode.CLAMP));
Path path = new Path();
path.setFillType(FillType.EVEN_ODD);
// A rectangle bounding the complete shadow.
RectF shadowRect = new RectF(outline);
shadowRect.inset(-shadowSize, -shadowSize);
// A rectangle with edges corresponding to the straight edges of the outline.
RectF inset = new RectF(outline);
inset.inset(radius, radius);
// A rectangle used to represent the edge shadow.
RectF edgeShadowRect = new RectF();
// left and right sides.
edgeShadowRect.set(-shadowSize, 0f, 0f, inset.height());
// Left shadow
sideShadow(canvas, edgePaint, edgeShadowRect, outline.left, inset.top, 0);
// Right shadow
sideShadow(canvas, edgePaint, edgeShadowRect, outline.right, inset.bottom, 2);
// Top shadow
edgeShadowRect.set(-shadowSize, 0, 0, inset.width());
sideShadow(canvas, edgePaint, edgeShadowRect, inset.right, outline.top, 1);
// bottom shadow. This needs an inset so that blank doesn't appear when the content is
// moved up.
edgeShadowRect.set(-shadowSize, 0, shadowSize / 2f, inset.width());
edgePaint.setShader(new LinearGradient(edgeShadowRect.right, 0, edgeShadowRect.left, 0,
colors, new float[]{0f, 1 / 3f, 1f}, TileMode.CLAMP));
sideShadow(canvas, edgePaint, edgeShadowRect, inset.left, outline.bottom, 3);
// Draw corners.
drawCorner(canvas, cornerPaint, path, inset.right, inset.bottom, outerArcRadius, 0);
drawCorner(canvas, cornerPaint, path, inset.left, inset.bottom, outerArcRadius, 1);
drawCorner(canvas, cornerPaint, path, inset.left, inset.top, outerArcRadius, 2);
drawCorner(canvas, cornerPaint, path, inset.right, inset.top, outerArcRadius, 3);
} finally {
canvas.restoreToCount(saved);
}
}
private static float elevationToShadow(float elevation) {
// The factor is chosen by eyeballing the shadow size on device and preview.
return elevation * 0.5f;
}
/**
* Translate canvas by half of shadow size up, so that it appears that light is coming
* slightly from above. Also, remove clipping, so that shadow is not clipped.
*/
private static int modifyCanvas(Canvas canvas, float shadowSize) {
Rect clipBounds = canvas.getClipBounds();
if (clipBounds.isEmpty()) {
return -1;
}
int saved = canvas.save();
// Usually canvas has been translated to the top left corner of the view when this is
// called. So, setting a clip rect at 0,0 will clip the top left part of the shadow.
// Thus, we just expand in each direction by width and height of the canvas.
canvas.clipRect(-canvas.getWidth(), -canvas.getHeight(), canvas.getWidth(),
canvas.getHeight(), Op.REPLACE);
canvas.translate(0, shadowSize / 2f);
return saved;
}
private static void sideShadow(Canvas canvas, Paint edgePaint,
RectF edgeShadowRect, float dx, float dy, int rotations) {
if (isRectEmpty(edgeShadowRect)) {
return;
}
int saved = canvas.save();
canvas.translate(dx, dy);
canvas.rotate(rotations * PERPENDICULAR_ANGLE);
canvas.drawRect(edgeShadowRect, edgePaint);
canvas.restoreToCount(saved);
}
/**
* @param canvas Canvas to draw the rectangle on.
* @param paint Paint to use when drawing the corner.
* @param path A path to reuse. Prevents allocating memory for each path.
* @param x Center of circle, which this corner is a part of.
* @param y Center of circle, which this corner is a part of.
* @param radius radius of the arc
* @param rotations number of quarter rotations before starting to paint the arc.
*/
private static void drawCorner(Canvas canvas, Paint paint, Path path, float x, float y,
float radius, int rotations) {
int saved = canvas.save();
canvas.translate(x, y);
path.reset();
path.arcTo(-radius, -radius, radius, radius, rotations * PERPENDICULAR_ANGLE,
PERPENDICULAR_ANGLE, false);
path.lineTo(0, 0);
path.close();
canvas.drawPath(path, paint);
canvas.restoreToCount(saved);
}
/**
* Differs from {@link RectF#isEmpty()} as this first converts the rect to int and then checks.
* <p/>
* This is required because {@link Canvas_Delegate#native_drawRect(long, float, float, float,
* float, long)} casts the co-ordinates to int and we want to ensure that it doesn't end up
* drawing empty rectangles, which results in IllegalArgumentException.
*/
private static boolean isRectEmpty(RectF rect) {
return (int) rect.left >= (int) rect.right || (int) rect.top >= (int) rect.bottom;
}
}