Android效能優化之圖片大小，尺寸壓縮綜合解決方案

@WorkerThread
public boolean compress(CompressFormat format, int quality, OutputStream stream) {
    checkRecycled("Can't compress a recycled bitmap");
    // do explicit check before calling the native method
    if (stream == null) {
        throw new NullPointerException();
    }
    if (quality < 0 || quality > 100) {
        throw new IllegalArgumentException("quality must be 0..100");
    }
    StrictMode.noteSlowCall("Compression of a bitmap is slow");
    Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, "Bitmap.compress");
    boolean result = nativeCompress(mNativePtr, format.nativeInt,
            quality, stream, new byte[WORKING_COMPRESS_STORAGE]);
    Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
    return result;
}

val baos= ByteArrayoutputstream ()
    try {
        var quality = 50
        do {
            quality -= 10
            baos.reset()
            bitmap.compress(Bitmap.CompressFormat.JPEG, quality, baos)
        } while (baos.toByteArray().size / 1024 > 100)
        fos.write(baos.toByteArray(o))
    }catch (ex : Throwable) {
        ex.printStackTrace ()} finally {
        fos.apply i this: FileOutputStream
        flush ()
        close ()
    }

    val reqWidth = 500
    val reqHeight = 300
    val bitmap = decodeSampledBitmapFromFile(imageFile, reqWidth, reqHeight)
    val fos = Fileoutputstream(
            File(applicationContext.filesDir,
                    child: "$ {system.currentTimeMillis() }_scale.jpg")
    )
    try {
        val quality = 50
        bitmap.compress(Bitmap.CompressFormat.JPEG, quality, fos)
        catch(ex: Throwable) {
            ex.printstackTrace() finally {
                fos.apply {
                    flush()
                    close()

                }
            }
        }
    }
}

private fun decodeSampledBitmapFromFile(imageFile: File，reqWidth: Int,reqHeight: Int): Bitmap
{
    return BitmapFactory.Options().run {
        inJustDecodeBounds = true
        //先獲取原始圖片的寬高，不會將Bitmap載入到記憶體中，返回null
        BitmapFactory.decodeFile(imageFile.absolutePath, opts: this)
        inSamplesize = calculateInSampleSize(options: this, reqWidth，reqHeight)
        inJustDecodeBounds - false
        BitmapFactory.decodeFile(imageFile.absolutePath， opts : this)
    }
}

private fun calculateInSampleSize(context: BitmapFactory, reqWidth: Int, reqHeight: Int): Int {
    //解構語法，獲取原始圖片的寬高
    val (height: Int, width: Int) = options.run { outHeight to outwidth }
    //計算最大的inSampleSize值，該值為2的冪次方，並同時保持這兩個值高度和寬度大於請求的高度和寬度。
    //原始圖片的寬高要大於要求的寬高
    var inSampleSize = 1
    if (height > reqHeight || width > reqWidth) {
        val halfHeight: Int = height / 2
        val halfwidth: Int = width / 2
        while (halfHeight / inSampleSize >= reqHeight && halfwidth / inSampleSize >= reqWidth) {
            inSampleSize *= 2
        }
    }
    return inSampleSize
}

int generateCompressJPEG(BYTE *data, int w, int h, int quality, const char *outfileName, jboolean optimize) {
    //結構體相當於java的類
    struct jpeg_compress_struct jcs;
    //當讀完整個檔案的時候回回撥
    struct my_error_mgr jem;
    jcs.err = jpeg_std_error(&jem.pub);
    jem.pub.error_exit = my_error_exit;
    //setjmp是一個系統級函數，是一個回撥
    if (setjmp(jem.setjmp_buffer)) {
        return 0;
    }
    //初始化jsc結構體
    jpeg_create_compress(&jcs);
    //開啟輸出檔案  wb可寫  rb可讀
    FILE *f = fopen(outfileName, "wb");
    if (f == NULL) {
        return 0;
    }
    //設定結構體的檔案路徑，以及寬高
    jpeg_stdio_dest(&jcs, f);
    jcs.image_width = w;
    jcs.image_height = h;
    //TRUE=arithmetic coding, FALSE=Huffman
    jcs.arith_code = false;
    int nComponent = 3;
    // 顏色的組成rgb，三個 of color components in input image
    jcs.input_components = nComponent;
    // 設定顏色空間為rgb
    jcs.in_color_space = JCS_RGB;
    jpeg_set_defaults(&jcs);
    // 是否採用哈夫曼
    jcs.optimize_coding = optimize;
    //設定質量
    jpeg_set_quality(&jcs, quality, true);
    //開始壓縮
    jpeg_start_compress(&jcs, TRUE);
    JSAMPROW row_pointer[1];
    int row_stride;
    row_stride = jcs.image_width * nComponent;
    while (jcs.next_scanline < jcs.image_height) {
        //得到一行的首地址
        row_pointer[0] = &data[jcs.next_scanline * row_stride];
        jpeg_write_scanlines(&jcs, row_pointer, 1);
    }
    // 壓縮結束
    jpeg_finish_compress(&jcs);
    // 銷燬回收記憶體
    jpeg_destroy_compress(&jcs);
    //關閉檔案
    fclose(f);
    return 1;
}

for (int i = 0; i < bitmapInfo.height; ++i) {
    for (int j= 0; j < bitmapInfo.width; ++j){
        if (bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGBA_8888){
            //0x2312faff ->588446463
            color = *(int *) (pixelsColor);
            // 從color值中讀取RGBA的值/ /ABGR
            b = (color >> 16)& 0xFE;
            g = (color >> 8)& OxFF;
            r = (color >> 0) & OxFF;
            *data = r;
            * (data + 1) =g;
            *(data + 2) = b;
            data += 3;
            //移動步長4個位元組
            pixelsColor +- 4 ;
        }else {
            return -2;
        }
        
    // 是否採用哈夫曼
     jcs.optimize_coding = optimize;

boolean result = nativeCompress(mNativePtr, format.nativeInt,
        quality, stream, new byte[WORKING_COMPRESS_STORAGE]);

private static native boolean nativeCompress(long nativeBitmap, int format,
                                        int quality, OutputStream stream,
                                        byte[] tempStorage);