BitmapLoadUtils.calculateInSampleSize() method optimization

[jiaowenzheng]

In some cases, the width of the image may be much larger than the height, for example, panorama. Smaple does not calculate the correct value. This one is a little bit better.

    /**
     * Calculate an inSampleSize for use in a
     * {@link android.graphics.BitmapFactory.Options} object when decoding
     * bitmaps using the decode* methods from
     * {@link android.graphics.BitmapFactory}. This implementation calculates
     * the closest inSampleSize that is a power of 2 and will result in the
     * final decoded bitmap having a width and height equal to or larger than
     * the requested width and height.
     *
     * @param options
     *            An options object with out* params already populated (run
     *            through a decode* method with inJustDecodeBounds==true
     * @param reqWidth
     *            The requested width of the resulting bitmap
     * @param reqHeight
     *            The requested height of the resulting bitmap
     * @return The value to be used for inSampleSize
     */
    public static int calculateInSampleSize(BitmapFactory.Options options,
                                            int reqWidth, int reqHeight) {
        // BEGIN_INCLUDE (calculate_sample_size)
        // Raw height and width of image
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {

            final int halfHeight = height / 2;
            final int halfWidth = width / 2;

            // Calculate the largest inSampleSize value that is a power of 2 and
            // keeps both
            // height and width larger than the requested height and width.
            while ((halfHeight / inSampleSize) > reqHeight
                    && (halfWidth / inSampleSize) > reqWidth) {
                inSampleSize *= 2;
            }

            // This offers some additional logic in case the image has a strange
            // aspect ratio. For example, a panorama may have a much larger
            // width than height. In these cases the total pixels might still
            // end up being too large to fit comfortably in memory, so we should
            // be more aggressive with sample down the image (=larger
            // inSampleSize).

            long totalPixels = width * height / inSampleSize;

            // Anything more than 2x the requested pixels we'll sample down
            // further
            final long totalReqPixelsCap = reqWidth * reqHeight * 2;

            while (totalPixels > totalReqPixelsCap) {
                inSampleSize *= 2;
                totalPixels /= 2;
            }
        }
        return inSampleSize;
        // END_INCLUDE (calculate_sample_size)
    }