Android相机预览闪烁

Question

我在使用SurfaceView进行相当简单的Android相机预览时遇到了问题。 我不知道为什么，但只要SurfaceView大小/位置落在可见区域之外，预览就会开始闪烁。如果相机看到的物体在移动，则强度会增加。

设备：Nexus 7（第一版），Android 4.4.2 针对API16的应用程序。

一旦闪烁发生，在日志中会显示如下所示的大量信息：

I/hwcomposer(  127): Setting interactive mode: Off
I/hwcomposer(  127): Setting interactive mode: On
I/hwcomposer(  127): Setting interactive mode: Off
I/hwcomposer(  127): Setting interactive mode: On
I/hwcomposer(  127): Setting interactive mode: Off

问题始于Sony Tablet Z，并在Nexus 7上重现。 出于某种原因，我不想在这里讨论如果预览区域落在可见区域之外，我没有完全控制。正如您所看到的，即使是（-100，-100）左/上边距的小预览也会导致问题。

该应用程序非常简单。只有一个类和XML布局文件：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <!-- 
        android:layout_width="1022px"
        android:layout_height="1363px"
        android:layout_marginLeft="0px"
        android:layout_marginTop="0px"
     -->
    <FrameLayout
        android:id="@+id/camera_preview_container"
        android:layout_width="500px"
        android:layout_height="500px"
        android:layout_marginLeft="-100px"
        android:layout_marginTop="-100px">        
        <SurfaceView
            android:id="@+id/surface_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>
    </FrameLayout>
</FrameLayout>

和活动代码：

package com.example.surfaceviewtest;

import java.io.IOException;

import android.hardware.Camera;
import android.hardware.Camera.CameraInfo;
import android.hardware.Camera.Size;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.util.Log;
import android.view.Menu;
import android.view.Surface;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.WindowManager;

public class MainActivity extends Activity  implements SurfaceHolder.Callback {
    private final String TAG = "com.example.surfaceviewtest";

    private Camera camera;
    private boolean isPreviewing = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ((SurfaceView)this.findViewById(R.id.surface_view)).getHolder().addCallback(this);      
    }

    @Override
    protected void onResume() {
        Log.d(TAG, "onResume");

        super.onResume();       
        camera = Camera.open(0);
        Camera.Parameters cameraParameters = camera.getParameters();
        Size previewSize = cameraParameters.getPreviewSize();
        Log.d(TAG, String.format("Preview size: width %d height %d", previewSize.width, previewSize.height));

        Size pictureSize = cameraParameters.getPictureSize();
        Log.d(TAG, String.format("Picture size: width %d height %d", pictureSize.width, pictureSize.height));
        /*cameraParameters.setPictureSize(320, 240);
        cameraParameters.setPreviewSize(176, 144);
        camera.setParameters(cameraParameters);*/
    }

    @Override
    protected void onPause() {
        Log.d(TAG, "onPause");

        super.onPause();
        stopPreview();
        camera.release();
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        Log.d(TAG, "surfaceCreated");

        try {
            setCameraDisplayOrientation();
            setCameraOrientation();
            camera.setPreviewDisplay(holder);
            startPreview();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width,
            int height) {
        Log.d(TAG, String.format ("surfaceChanged: format %d width %d height %d", format, width, height));      
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        Log.d(TAG, "surfaceDestroyed");
        stopPreview();
    }

    private void startPreview() {
        if (isPreviewing)
            return;

        camera.startPreview();
    }

    private void stopPreview() {
        if (isPreviewing == false)
            return;

        camera.stopPreview();
        isPreviewing = false;
    }

    public int getDisplayOrientation() {
        android.hardware.Camera.CameraInfo info = new android.hardware.Camera.CameraInfo();
        android.hardware.Camera.getCameraInfo(0, info);
        int rotation = ((WindowManager) getSystemService(
                Context.WINDOW_SERVICE)).getDefaultDisplay().getRotation();
        int degrees = orientationToAngle(rotation);

        int result;
        if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
            result = (info.orientation + degrees) % 360;
            result = (360 - result) % 360; // compensate the mirror
        } else { // back-facing
            result = (info.orientation - degrees + 360) % 360;
        }
        return result;
    }

    protected void setCameraDisplayOrientation() {
        int rotation = getDisplayOrientation();
        camera.setDisplayOrientation(rotation);
    }

    protected static int orientationToAngle(int orientation) {
        switch (orientation) {
        case Surface.ROTATION_0:
            return 0;
        case Surface.ROTATION_90:
            return 90;
        case Surface.ROTATION_180:
            return 180;
        case Surface.ROTATION_270:
            return 270;
        }
        return 0;

    }

    protected void setCameraOrientation() {
        int orientation = ((WindowManager) getSystemService(
                Context.WINDOW_SERVICE)).getDefaultDisplay().getRotation();
        int degrees = orientationToAngle(orientation);
        android.hardware.Camera.CameraInfo info = new android.hardware.Camera.CameraInfo();
        android.hardware.Camera.getCameraInfo(0, info);
        degrees = (degrees + 45) / 90 * 90;
        int rotation = 0;
        if (info.facing != CameraInfo.CAMERA_FACING_FRONT) {
            rotation = (info.orientation - degrees + 360) % 360;
        } else { 
            rotation = (info.orientation + degrees) % 360;
        }

        Camera.Parameters parameters = camera.getParameters();
        parameters.setRotation(rotation);
        camera.setParameters(parameters);
    }
}