[android-developers] How to convert screen coordination to camera's driver coordination

Hi all,

I'm a newbie for Android programming and I'm making a code to control the camera by using API.
I'm struggling with the problem to map the screen coordination to camera's driver coordination for a long time.

(Development Env: Samsung Galaxy S3 & Eclipse)

I'd like to implement to show the rectangle in the screen when the user click the preview.
Actually there is no problem in establishing this but the problem is that
- I got wrong location with the coordination in the preview and the coordination in the camera focus area when I get the coordination to use getFocusArea

I translate the screen coordination to camera driver coordination by using the matrix.
Below is to initiate the matrix:
----------------------------

public static void prepareMatrix(Matrix matrix, boolean mirror, int displayOrientation, int viewWidth, int viewHeight) {

         // Need mirror for front camera.

         matrix.setScale(mirror ? -1 : 1, 1);

         // This is the value for android.hardware.Camera.setDisplayOrientation.

         matrix.postRotate(displayOrientation);

           // Camera driver coordinates range from (-1000, -1000) to (1000, 1000).

            // UI coordinates range from (0, 0) to (width, height).

             matrix.postScale(viewWidth / 2000f, viewHeight / 2000f);

             matrix.postTranslate(viewWidth / 2f, viewHeight / 2f);

} 

I've got this code in the internet.

Below is to convert the coordination:
---------------------

void calculateTapArea(int focusWidth, int focusHeight, float areaMultiple, int x, int y, int previewWidth, int previewHeight, Rect rect) {

            int areaWidth = (int) (focusWidth * areaMultiple);

              int areaHeight = (int) (focusHeight * areaMultiple);

             int left = Util.clamp(x - areaWidth / 2, 0, previewWidth - areaWidth);

              int top = Util.clamp(y - areaHeight / 2, 0, previewHeight - areaHeight);

            RectF rectF = new RectF(left, top, left + areaWidth, top + areaHeight);

            this.gCoordinationConvertMatrix.mapRect(rectF);

           Util.rectFToRect(rectF, rect);

}

And finally below is to call above function. _x & _y is the screen coordination:
-----------------

        ArrayList<Area> mFocusArea = new ArrayList<Area>();

       mFocusArea.add(new Area(new Rect(), 1));

       ArrayList<Area> mMeteringArea =new ArrayList<Area>();

      mMeteringArea.add(new Area(new Rect(), 1));

       calculateTapArea(_100, _100, 1f, _x, _y,

        this.gPreview.getWidth(), this.gPreview.getHeight(), mFocusArea.get(0).rect);

         calculateTapArea(_100, _100, 1.5f, _x, _y,

         this.gPreview.getWidth(), this.gPreview.getHeight(), mMeteringArea.get(0).rect);

......

After this code, I just set the Auto Focus by setting the focus & metering area by using setFocusArea & setMeteringArea function.

Strange thing is I set the orientation as 'Landscape' in the manifest file so when I click the upper right corner when the phone vertically stand up, preview coordination returns 0,0 as expected. but after conversion, above function also returns 0,0. I think it should be -1000, -1000.

All codes above is from the Internet.
I thinks I'm doing wrong to display the focus area when the user click the preview screen.
If you know better idea or any hint then please let me know.

Thank you.

PS: Sorry for my poor English.

Brief Summary:
------------------
I'd like to get the correct focus area when the user click the preview area. But I got wrong focus area after setFocusArea to the camera after converting the preview coordination.

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