在Android系统中,如何将图形置于相机预览之上?

我在这个话题上看到了一些线索,但似乎没有一个能回答这个问题,所以,我要再尝试一下……

非常简单的想法…我想在屏幕的某些部分预览(和拍摄)相机,而在屏幕的其他部分添加我自己的图形元素(按钮、围绕相机预览的彩色框架等)。

Android附带的示例将填充屏幕。显而易见的解决方案(似乎不起作用)是使用我自己的SurfaceView(而不是示例中的SurfaceView),并将其放在我的XML中。代码(下面)不会崩溃,并报告它正在启动摄像头…它从不在屏幕上渲染。

我不知道我做错了什么。我的猜测是,它与显示线程有某种关系,在它渲染初始屏幕后,它从来没有重新绘制任何东西的冲动,但我甚至尝试添加一个按钮,并在单击按钮时启动相机在表面视图上渲染,但这并没有进一步激发它。 (大部分代码是直接从Android示例代码中提取出来的,因此,我确信它是正确的。我想,我只是做了一些错误的事情,我想,我是在事后把我的观点拉进去的。

任何帮助都非常感谢。

public class TakePhoto extends Activity implements SurfaceHolder.Callback{
    /** Called when the activity is first created. */
    SurfaceHolder mHolder;
    Camera mCamera;


@Override
protected void onCreate(Bundle savedInstanceState) {            
    super.onCreate(savedInstanceState);


    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
    WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.take_photo);        

    try{
        SurfaceView sv = (SurfaceView) findViewById(R.id.camera_surface);
        mHolder = sv.getHolder();
        mHolder.addCallback(this);     
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);  
        toast("added callback");
    }catch(Exception e){
        toast("push: " + e);
    }       
}


public void surfaceCreated(SurfaceHolder holder) {

    mCamera = Camera.open();
    try {

       mCamera.setPreviewDisplay(mHolder);
    } catch (IOException exception) {
        mCamera.release();
        mCamera = null;
        toast("error:" + exception);
    }
}

public void surfaceDestroyed(SurfaceHolder holder) {
    mCamera.stopPreview();
    mCamera.release();
    mCamera = null;
}


private Size getOptimalPreviewSize(List<Size> sizes, int w, int h) {
    final double ASPECT_TOLERANCE = 0.05;
    double targetRatio = (double) w / h;
    if (sizes == null) return null;

    Size optimalSize = null;
    double minDiff = Double.MAX_VALUE;

    int targetHeight = h;


    for (Size size : sizes) {
        double ratio = (double) size.width / size.height;
        if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) continue;
        if (Math.abs(size.height - targetHeight) < minDiff) {
            optimalSize = size;
            minDiff = Math.abs(size.height - targetHeight);
        }
    }


    if (optimalSize == null) {
        minDiff = Double.MAX_VALUE;
        for (Size size : sizes) {
            if (Math.abs(size.height - targetHeight) < minDiff) {
                optimalSize = size;
                minDiff = Math.abs(size.height - targetHeight);
            }
        }
    }
    return optimalSize;
}

public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {

    Camera.Parameters parameters = mCamera.getParameters();

    List<Size> sizes = parameters.getSupportedPreviewSizes();
    Size optimalSize = getOptimalPreviewSize(sizes, w, h);        

    parameters.setPreviewSize(optimalSize.width, optimalSize.height);        

    mCamera.setParameters(parameters);
    mCamera.startPreview();
}

private void toast(String str){
    Context context = getApplicationContext();       
    int duration = Toast.LENGTH_SHORT;
    Toast toast = Toast.makeText(context, str, duration);
    toast.show();

}

}