Android Camera开发系列：设置对焦模式模式

一、有哪几种对焦模式？
二、如何使用各种对焦模式？

----- Camera.java

        public String getFocusMode() {
            return get(KEY_FOCUS_MODE);
        }

----- CameraCharacteristics.java

    @PublicKey
    public static final Key<int[]> CONTROL_AF_AVAILABLE_MODES =
            new Key<int[]>("android.control.afAvailableModes", int[].class);

    public static final String FOCUS_MODE_AUTO = "auto";
    public static final String FOCUS_MODE_FIXED = "fixed";
    public static final String FOCUS_MODE_CONTINUOUS_VIDEO = "continuous-video";
    public static final String FOCUS_MODE_CONTINUOUS_PICTURE = "continuous-picture";

   FOCUS_MODE_AUTO：自动对焦，这个只会触发一次对焦，并且是需要在预览开启后，调用autoFocus接口后才会触发，
像触点对焦、和拍照对焦都可以用到该模式；
   FOCUS_MODE_FIXED：定焦，有些摄像头本身不支持对焦；
   FOCUS_MODE_CONTINUOUS_VIDEO：录像的时候，可以采用该模式，会持续对焦，设置parameter参数后就会生效；
   FOCUS_MODE_CONTINUOUS_PICTURE ：拍照的时候，可以采用该模式，会持续对焦，设置parameter参数后就会生效，对焦速度相对 
   FOCUS_MODE_CONTINUOUS_VIDEO 会快点；

      public final void autoFocus(AutoFocusCallback cb)
      {
        ...
       }

      public void setFocusMode(String value) {
            ...
      }

      public void setParameters(Parameters params) {
         ...
       }

      public final void cancelAutoFocus()
      {
        ...
      }

request.set(CaptureRequest.CONTROL_AF_MODE, int focusMode);

       /**
         * Auto-focus mode. Applications should call {@link
         * #autoFocus(AutoFocusCallback)} to start the focus in this mode.
         */
        public static final String FOCUS_MODE_AUTO = "auto";

        /**
         * Focus is set at infinity. Applications should not call
         * {@link #autoFocus(AutoFocusCallback)} in this mode.
         */
        public static final String FOCUS_MODE_INFINITY = "infinity";

        /**
         * Macro (close-up) focus mode. Applications should call
         * {@link #autoFocus(AutoFocusCallback)} to start the focus in this
         * mode.
         */
        public static final String FOCUS_MODE_MACRO = "macro";

        /**
         * Focus is fixed. The camera is always in this mode if the focus is not
         * adjustable. If the camera has auto-focus, this mode can fix the
         * focus, which is usually at hyperfocal distance. Applications should
         * not call {@link #autoFocus(AutoFocusCallback)} in this mode.
         */
        public static final String FOCUS_MODE_FIXED = "fixed";

        /** @hide
         * Normal focus mode. Applications should call
         * {@link #autoFocus(AutoFocusCallback)} to start the focus in this
         * mode.
         */
        public static final String FOCUS_MODE_NORMAL = "normal";

        /**
         * Extended depth of field (EDOF). Focusing is done digitally and
         * continuously. Applications should not call {@link
         * #autoFocus(AutoFocusCallback)} in this mode.
         */
        public static final String FOCUS_MODE_EDOF = "edof";

        /**
         * Continuous auto focus mode intended for video recording. The camera
         * continuously tries to focus. This is the best choice for video
         * recording because the focus changes smoothly . Applications still can
         * call {@link #takePicture(Camera.ShutterCallback,
         * Camera.PictureCallback, Camera.PictureCallback)} in this mode but the
         * subject may not be in focus. Auto focus starts when the parameter is
         * set.
         *
         * <p>Since API level 14, applications can call {@link
         * #autoFocus(AutoFocusCallback)} in this mode. The focus callback will
         * immediately return with a boolean that indicates whether the focus is
         * sharp or not. The focus position is locked after autoFocus call. If
         * applications want to resume the continuous focus, cancelAutoFocus
         * must be called. Restarting the preview will not resume the continuous
         * autofocus. To stop continuous focus, applications should change the
         * focus mode to other modes.
         *
         * @see #FOCUS_MODE_CONTINUOUS_PICTURE
         */
        public static final String FOCUS_MODE_CONTINUOUS_VIDEO = "continuous-video";

        /**
         * Continuous auto focus mode intended for taking pictures. The camera
         * continuously tries to focus. The speed of focus change is more
         * aggressive than {@link #FOCUS_MODE_CONTINUOUS_VIDEO}. Auto focus
         * starts when the parameter is set.
         *
         * <p>Applications can call {@link #autoFocus(AutoFocusCallback)} in
         * this mode. If the autofocus is in the middle of scanning, the focus
         * callback will return when it completes. If the autofocus is not
         * scanning, the focus callback will immediately return with a boolean
         * that indicates whether the focus is sharp or not. The apps can then
         * decide if they want to take a picture immediately or to change the
         * focus mode to auto, and run a full autofocus cycle. The focus
         * position is locked after autoFocus call. If applications want to
         * resume the continuous focus, cancelAutoFocus must be called.
         * Restarting the preview will not resume the continuous autofocus. To
         * stop continuous focus, applications should change the focus mode to
         * other modes.
         *
         * @see #FOCUS_MODE_CONTINUOUS_VIDEO
         */
        public static final String FOCUS_MODE_CONTINUOUS_PICTURE = "continuous-picture";