Android Bitmap conversion operations: scale, crop, rotate, offset

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/**
     * 根据给定的宽和高进行拉伸
     *
     * @param origin    原图
     * @param newWidth  新图的宽
     * @param newHeight 新图的高
     * @return new Bitmap
     */
    private Bitmap scaleBitmap(Bitmap origin, int newWidth, int newHeight) {
        if (origin == null) {
            return null;
        }
        int height = origin.getHeight();
        int width = origin.getWidth();
        float scaleWidth = ((float) newWidth) / width;
        float scaleHeight = ((float) newHeight) / height;
        Matrix matrix = new Matrix();
        matrix.postScale(scaleWidth, scaleHeight);// 使用后乘
        Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
        if (!origin.isRecycled()) {
            origin.recycle();
        }
        return newBM;
    }

    /**
     * 按比例缩放图片
     *
     * @param origin 原图
     * @param ratio  比例
     * @return 新的bitmap
     */
    private Bitmap scaleBitmap(Bitmap origin, float ratio) {
        if (origin == null) {
            return null;
        }
        int width = origin.getWidth();
        int height = origin.getHeight();
        Matrix matrix = new Matrix();
        matrix.preScale(ratio, ratio);
        Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
        if (newBM.equals(origin)) {
            return newBM;
        }
        origin.recycle();
        return newBM;
    }

    /**
     * 裁剪
     *
     * @param bitmap 原图
     * @return 裁剪后的图像
     */
    private Bitmap cropBitmap(Bitmap bitmap) {
        int w = bitmap.getWidth(); // 得到图片的宽，高
        int h = bitmap.getHeight();
        int cropWidth = w >= h ? h : w;// 裁切后所取的正方形区域边长
        cropWidth /= 2;
        int cropHeight = (int) (cropWidth / 1.2);
        return Bitmap.createBitmap(bitmap, w / 3, 0, cropWidth, cropHeight, null, false);
    }

    /**
     * 选择变换
     *
     * @param origin 原图
     * @param alpha  旋转角度，可正可负
     * @return 旋转后的图片
     */
    private Bitmap rotateBitmap(Bitmap origin, float alpha) {
        if (origin == null) {
            return null;
        }
        int width = origin.getWidth();
        int height = origin.getHeight();
        Matrix matrix = new Matrix();
        matrix.setRotate(alpha);
        // 围绕原地进行旋转
        Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
        if (newBM.equals(origin)) {
            return newBM;
        }
        origin.recycle();
        return newBM;
    }

    /**
     * 偏移效果
     * @param origin 原图
     * @return 偏移后的bitmap
     */
    private Bitmap skewBitmap(Bitmap origin) {
        if (origin == null) {
            return null;
        }
        int width = origin.getWidth();
        int height = origin.getHeight();
        Matrix matrix = new Matrix();
        matrix.postSkew(-0.6f, -0.3f);
        Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
        if (newBM.equals(origin)) {
            return newBM;
        }
        origin.recycle();
        return newBM;
    }