在Camera preview上叠加drawable元素

例子中将演示android.graphics.Canvas 和 android.hardware.Camera 的用法。
源代码 (Java)：
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.hardware.Camera;
import android.os.Bundle;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.view.Window;
import android.view.ViewGroup.LayoutParams;
public class TestCameraOverlay extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
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