Android NDK使用libjpeg解析JPEG图片,并显示到SurfaceView上

SurfaceView大概是谷歌提供给开发者最吸引人的的组件了,原因是SurfaceView的界面刷新允许在非UI线程中更新,正因为此,很多频繁更新界面的应用,如视频播放器、游戏、动画效果总会基于SurfaceView及其子类进行开发。

而最近我正在研究的一个应用是关于处理图片并显示图片的应用,图片实在是内存杀手,而处理图片则运算量非常大,这些都是令人头疼的问题。

分析应用,并选择实现技术

1、处理图片运算量大,为了提高运算效率,选择使用C语言处理图片

2、需要的内存空间较大,为节约内存并提高效率,需要从C语言中读入文件,并及早释放

下面写下展示图片的基本流程

1、用户选择图片

2、获得用户选择的图片的路径

3、调用展示图片的方法(C方法)

第一部分:用户选择图片

Intent intent = new Intent(Intent.ACTION_GET_CONTENT);// ACTION_OPEN_DOCUMENT
intent.addCategory(Intent.CATEGORY_OPENABLE);
intent.setType("image/jpeg");
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.KITKAT) {
	startActivityForResult(intent, SELECT_PIC_KITKAT);
} else {
	startActivityForResult(intent, SELECT_PIC);
}

第二部分获得用户选择的图片的路径

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
		if (resultCode == RESULT_OK) {

			if (requestCode == SELECT_PIC) {
				Uri originalUri = data.getData();
				String[] proj = { MediaStore.Images.Media.DATA };
				// 好像是android多媒体数据库的封装接口，具体的看Android文档
				Cursor cursor = managedQuery(originalUri, proj, null, null,
						null);
				// 按我个人理解 这个是获得用户选择的图片的索引值
				int column_index = cursor
						.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
				// 将光标移至开头 ，这个很重要，不小心很容易引起越界
				cursor.moveToFirst();
				// 最后根据索引值获取图片路径
				String path = cursor.getString(column_index);
				Log.v("图片路径: ", path);

				if (path.endsWith(".jpg")) {
					isOnActivityResult = true;
					imgPath = path;
				}
			}
		}
	};

第三部分:调用展示图片的方法

这个部分需要注意,写在SurfaceHolder的回调方法内,为的是让SurfaceView中的Surface成功建立后,再将Surface传入C代码中进行处理

<span style="white-space:pre">		</span>svShow = (SurfaceView) findViewById(R.id.svShow);
		svHolder = svShow.getHolder();

		svHolder.addCallback(new SurfaceHolder.Callback() {

			public void surfaceChanged(SurfaceHolder holder, int format,
					int width, int height) {
				Log.v(TAG, "surfaceChanged format=" + format + ", width="
						+ width + ", height=" + height);
			}

			public void surfaceCreated(SurfaceHolder holder) {
				Log.v(TAG, "surfaceCreated");
				if (isOnActivityResult && imgPath != null) {
					showJPG(holder.getSurface(), imgPath);
				}
			}

			public void surfaceDestroyed(SurfaceHolder holder) {
				Log.v(TAG, "surfaceDestroyed");
			}

		});

实际处理图片并显示图片的代码

JNIEXPORT void JNICALL Java_com_example_photoprocessing_activity_SurfaceProcessingActivity_showJPG(
		JNIEnv * env, jobject activity, jobject surface, jstring img) {
	const char * imgChar;
	jboolean * isCopy;
	imgChar = env->GetStringUTFChars(img, 0);
	ANativeWindow_Buffer nwBuffer;

	LOGI("img path : %s  ",imgChar);

	LOGI("ANativeWindow_fromSurface ");
	ANativeWindow * mANativeWindow = ANativeWindow_fromSurface(env, surface);

	if (mANativeWindow == NULL) {
		LOGE("ANativeWindow_fromSurface error");
		return;
	}

	LOGI("ANativeWindow_lock ");
	if (0 != ANativeWindow_lock(mANativeWindow, &nwBuffer, 0)) {
		LOGE("ANativeWindow_lock error");
		return;
	}

	read_jpeg_file_show(imgChar, nwBuffer);

	if (nwBuffer.format == WINDOW_FORMAT_RGBA_8888) {
		LOGI("nwBuffer->format == WINDOW_FORMAT_RGBA_8888 ");
	}

	LOGI("ANativeWindow_unlockAndPost ");
	if (0 != ANativeWindow_unlockAndPost(mANativeWindow)) {
		LOGE("ANativeWindow_unlockAndPost error");
		return;
	}

	env->ReleaseStringUTFChars(img,imgChar);
	ANativeWindow_release(mANativeWindow);
	LOGI("ANativeWindow_release ");
	return;
}

int read_jpeg_file_show(const char *input_filename,
		ANativeWindow_Buffer& nwBuffer) {
	struct jpeg_decompress_struct cinfo;
	struct jpeg_error_mgr jerr;
	FILE *input_file;
	JSAMPARRAY buffer;
	int row_width;

	unsigned char *buffertmp;

	cinfo.err = jpeg_std_error(&jerr);

	if ((input_file = fopen(input_filename, "rb")) == NULL) {
		fprintf(stderr, "can't open %s\n", input_filename);
		LOGI("can't open jpg1");
		return -1;
	}

	//初始化信息
	jpeg_create_decompress(&cinfo);
	LOGI("初始化信息");

	/* Specify data source for decompression */
	//指定图片
	jpeg_stdio_src(&cinfo, input_file);
	LOGI("指定图片");

	/* Read file header, set default decompression parameters */
	(void) jpeg_read_header(&cinfo, TRUE);
	LOGI("读取头信息, set default decompression parameters ");

	/* Start decompressor */
	(void) jpeg_start_decompress(&cinfo);
	LOGI("解压");

	row_width = cinfo.output_width * cinfo.output_components;
	LOGI(
			"图片的宽:%d 图片的高%d 颜色长度:%d", cinfo.output_width, cinfo.output_height, cinfo.output_components);

	buffer = (*cinfo.mem->alloc_sarray)((j_common_ptr) &cinfo, JPOOL_IMAGE,
			row_width, 1);

	//一行
	buffertmp = (unsigned char *) malloc(row_width);
	memset(buffertmp, 0, row_width);
	LOGI("malloc and memset");
//        tmp = output_buffer;

	/* Process data */
	int get8h5 = 248, get8h6 = 252;
	__uint16_t * line = (__uint16_t *) nwBuffer.bits;
	int wheight = 0;

	int scalew = 1, scaleh = 1;

	if (cinfo.output_width > nwBuffer.width) {
		scalew = cinfo.output_width / nwBuffer.width;
	}

	LOGI(" scale of img = %d", scalew);

	for (int i = 0, choosehNum = 0; i < cinfo.output_height; i++) {
		//获得一行
		jpeg_read_scanlines(&cinfo, buffer, 1);
		buffertmp = *buffer;
		//根据缩放选取行
		if (i % scalew == 0 && choosehNum++ < nwBuffer.height) {

			//LOGI("nwBuffer->format == WINDOW_FORMAT_RGB_565");
			for (int j = 0, choosewNum = 0; j < cinfo.output_width; j++) {
				if (j % scalew == 0) {
					if (nwBuffer.format == WINDOW_FORMAT_RGB_565) {
						line[choosewNum] = ((__uint16_t ) buffertmp[3 * j + 0]
								& get8h5) << 8
								| ((__uint16_t ) (buffertmp[3 * j + 1] & get8h6)
										<< 3)
								| ((__uint16_t ) (buffertmp[3 * j + 2] & get8h6)
										>> 3);
						choosewNum++;
					}
				}

			}
			line = line + nwBuffer.stride;
		}
	}

//                memcpy(tmp, *buffer, row_width);
//                tmp += row_width;

	(void) jpeg_finish_decompress(&cinfo);
	LOGI("jpeg_finish_decompress !!");

	jpeg_destroy_decompress(&cinfo);
	LOGI("jpeg_destroy_decompress !!");

	/* Close files, if we opened them */
	fclose(input_file);

	return 0;
}

Demo展示:

点击显示图片,开始选择图片:

选择完后,自动显示: