问题
I've got a custom view with the following code:
private final Drawable outerGauge;
private final Drawable innerGauge;
private float rotateX;
private float rotateY;
private int rotation = 0;
{
outerGauge = getContext().getDrawable(R.drawable.gauge_outer);
innerGauge = getContext().getDrawable(R.drawable.gauge_inner);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
outerGauge.draw(canvas);
canvas.rotate(rotation, rotateX, rotateY);
innerGauge.draw(canvas);
canvas.rotate(-rotation, rotateX, rotateY);
}
Most of the time this produces perfectly clear images. However, sometimes the result looks like this: This only seems to happen on one of my two test devices. The device is a Motorola moto G, with the Android 6 upgrade. The other test device, which always seems to produce perfectly clear images, is an Oneplus X, Android 5. It's also not consistent, it happens sometimes, and then doesn't again the next moment. From what I've been able to test, it does not even depend on the amount of rotation applied. I've never seen it happen on straight angles though, (0, 90, 180 degrees,) and it does seem to be worse at angles closer to 45 or 135 degrees.
The image in question is an imported SVG, placed directly in the res/drawable folder. Therefore it can't be the resolution. (Also, gauge_outer is placed in exactly the same folder and made exactly the same way, though this one does not become blurry.)
Any ideas on how to solve this?
Edit:
Okay, never mind what I said about the complete inconsistency. It appears to be fully consistent, and be worst when the rotation comes closer and closer to 90 degrees. Also, as soon as the rotation is exactly 90 degrees, the indicator completely disappears.
Edit:
Behold: two emulators, one running Android 5 and one running Android 6:
The full source code is as follows:
package nl.dvandenberg.gauge;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.View;
public class GaugeView extends View {
private static final int ORIGINAL_ROTATE_Y = 510;
private static final int ORIGINAL_IMAGE_HEIGHT = 613;
private static final int ORIGINAL_IMAGE_WIDTH = 1046;
private final Drawable outerGauge;
private final Drawable innerGauge;
private float rotateX;
private float rotateY;
private int rotation = 0;
{
outerGauge = getContext().getDrawable(R.drawable.gauge_outer);
innerGauge = getContext().getDrawable(R.drawable.gauge_inner);
}
public GaugeView(Context context) {
super(context);
setProgress(48);
}
public GaugeView(Context context, AttributeSet attrs) {
super(context, attrs);
setProgress(48);
}
public GaugeView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
setProgress(48);
}
public void setProgress(double percentage) {
this.rotation = (int) (180 * Math.min(100, Math.max(0, percentage)) / 100);
invalidate();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
double width = MeasureSpec.getSize(widthMeasureSpec);
double idealHeight = ORIGINAL_IMAGE_HEIGHT * width / ORIGINAL_IMAGE_WIDTH;
double height = Math.min(idealHeight, MeasureSpec.getSize(heightMeasureSpec));
width = width * height / idealHeight;
heightMeasureSpec = MeasureSpec.makeMeasureSpec((int) height, MeasureSpec.getMode(heightMeasureSpec));
rotateX = (float) (width / 2f);
rotateY = (float) (height / ORIGINAL_IMAGE_HEIGHT * ORIGINAL_ROTATE_Y);
outerGauge.setBounds(0, 0, (int) width, (int) height);
innerGauge.setBounds(0, 0, (int) width, (int) height);
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
outerGauge.draw(canvas);
canvas.rotate(rotation, rotateX, rotateY);
innerGauge.draw(canvas);
}
}
with drawable/gauge_inner.xml
<?xml version="1.0" encoding="utf-8"?>
<vector xmlns:android="http://schemas.android.com/apk/res/android"
android:width="1046dp"
android:height="613dp"
android:viewportWidth="1046"
android:viewportHeight="613">
<path
android:fillColor="#aa3939"
android:pathData="M142.541,516.071 C145.053,517.623,156.088,519.334,183.255,522.586
C203.832,525.024,251.438,530.676,289.03,535.184
C326.708,539.641,359.782,543.523,362.537,543.896
C365.292,544.268,388.127,547.018,413.445,550.067 L459.289,555.468
L462.946,560.401 C468.075,567.485,479.691,577.405,489.255,582.968
C499.701,589.062,520.069,594.737,531.817,594.883
C571.623,595.225,607.57,570.083,620.01,533.226
C624.956,518.592,626.123,507.412,624.269,492.201
C622.686,479.259,620.262,472.461,612.212,458.518
C602.012,440.852,592.681,431.69,575.424,422.602
C537.988,402.763,489.163,413.401,462.78,447.108 L458.957,452.086
L449.523,453.146 C444.316,453.727,420.115,456.614,395.829,459.552
C371.456,462.538,346.451,465.429,340.177,466.165
C333.904,466.9,293.067,471.772,249.427,476.991
C205.788,482.211,164.951,487.082,158.678,487.817
C144.122,489.408,139.036,491.998,136.796,498.719
C134.433,505.626,136.72,512.388,142.541,516.07 Z" />
</vector>
and drawable/gauge_outer.xml
<?xml version="1.0" encoding="utf-8"?>
<vector xmlns:android="http://schemas.android.com/apk/res/android"
android:width="1046dp"
android:height="613dp"
android:viewportWidth="1046"
android:viewportHeight="613">
<path
android:fillColor="#aa3939"
android:pathData="M488.981,0.56719 C465.882,2.06727,430.783,6.96753,412.984,11.0677
C392.285,15.768,387.285,17.0681,375.285,20.6683
C231.691,63.4706,113.696,164.376,49.898,299.183
C16.6993,369.187,0,444.491,0,523.495
C0,540.296,0.0999961,541.696,1.99992,543.596
C3.99984,545.596,5.29979,545.596,59.4977,545.596
C113.696,545.596,114.996,545.596,116.995,543.596
C118.895,541.696,118.995,540.296,118.995,522.595
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C499.979,113.271,500.079,114.671,501.979,116.572
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C713.772,145.773,707.973,156.973,707.973,158.573
C707.973,162.273,709.373,163.573,718.973,169.274
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C926.965,540.294,927.065,541.694,928.965,543.594
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C1009.06,325.382,990.461,284.58,971.762,253.578
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C555.278,0.16716,507.68,-0.63288,488.981,0.56719 Z" />
</vector>
回答1:
Though not an answer, I have managed to find a workaround. This workaround relies on drawing the image onto a canvas, which is linked to a bitmap, which is then drawn onto the final, rotated canvas in the onDraw method.
It seems like this problem really only arises with nodpi-drawables, in other words, imported svg's. It is however, very consistent. Whether the shape is a multi-path vector or a simple square does not matter, the problem will always take exactly the same shape, with images disappearing entirely when the canvas is rotated 90°.
The full code I used to bypass this problem is as follows:
package nl.dvandenberg.energymonitor.customViews;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.View;
import nl.dvandenberg.energymonitor.R;
public class GaugeView extends View {
private static final int ORIGINAL_ROTATE_Y = 510;
private static final int ORIGINAL_IMAGE_HEIGHT = 613;
private static final int ORIGINAL_IMAGE_WIDTH = 1046;
private final Drawable outerGauge, innerGauge;
private float rotateX;
private float rotateY;
private int rotation = 0;
private Bitmap innerGaugeBitmap;
private final Canvas innerGaugeCanvas;
{
outerGauge = getContext().getDrawable(R.drawable.gauge_outer);
innerGauge = getContext().getDrawable(R.drawable.gauge_inner);
innerGaugeCanvas = new Canvas();
}
public GaugeView(Context context) {
super(context);
}
public GaugeView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public GaugeView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public void setProgress(double percentage) {
this.rotation = (int) (180 * Math.min(100, Math.max(0, percentage)) / 100);
invalidate();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
double width = MeasureSpec.getSize(widthMeasureSpec);
double idealHeight = ORIGINAL_IMAGE_HEIGHT * width / ORIGINAL_IMAGE_WIDTH;
double height = Math.min(idealHeight, MeasureSpec.getSize(heightMeasureSpec));
width = width * height / idealHeight;
heightMeasureSpec = MeasureSpec.makeMeasureSpec((int) height, MeasureSpec.getMode(heightMeasureSpec));
rotateX = (float) (width / 2f);
rotateY = (float) (height / ORIGINAL_IMAGE_HEIGHT * ORIGINAL_ROTATE_Y);
outerGauge.setBounds(0, 0, (int) width, (int) height);
innerGauge.setBounds(0, 0, (int) width, (int) height);
if (innerGaugeBitmap != null){
innerGaugeBitmap.recycle();
}
innerGaugeBitmap = Bitmap.createBitmap((int) width, (int) height, Bitmap.Config.ARGB_8888); // Gives LINT-warning draw-allocation, but no other way to upscale bitmaps exists.
innerGaugeCanvas.setBitmap(innerGaugeBitmap);
innerGaugeBitmap.eraseColor(Color.TRANSPARENT);
innerGauge.draw(innerGaugeCanvas);
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
@Override
protected void onDraw(Canvas canvas) {
outerGauge.draw(canvas);
canvas.rotate(rotation, rotateX, rotateY);
canvas.drawBitmap(innerGaugeBitmap,0,0,null);
}
}
with the important part occuring in the onMeasure method:
if (innerGaugeBitmap != null){
innerGaugeBitmap.recycle();
}
innerGaugeBitmap = Bitmap.createBitmap((int) width, (int) height, Bitmap.Config.ARGB_8888); // Gives LINT-warning draw-allocation, but no other way to upscale bitmaps exists.
innerGaugeCanvas.setBitmap(innerGaugeBitmap);
innerGaugeBitmap.eraseColor(Color.TRANSPARENT);
innerGauge.draw(innerGaugeCanvas);
I have filed a bugreport at https://code.google.com/p/android/issues/detail?id=208453
来源：https://stackoverflow.com/questions/36868790/blurry-image-after-canvas-rotate-only-in-android-6