Android JNI library compiled SO achieve complete demo Gaussian blur effect

Long useless play jni ndk library compiled so, in order to prevent the hand gifted class with a Gaussian blur algorithm needs to be implemented recently practiced hand. Of course, this algorithm is not I realized that I just put this algorithm C code is compiled into a library so because C higher efficiency than java, as the algorithm is very suitable for eating CPU made SO file.

NDK and JNI not described here, and I would say the focus is compiled from a SO library to use this process.

The picture above you can see clear process C / C ++ code to generate the SO library and java layer code calls by KJNI environment.

I compiled with android studio, because SO is a java library and library files and load layer affirms method requires a corresponding interface so we can create a library module directly dependent on the engineering inside, began to explain complete the following steps:

 

(1) Create a new dependent libraries needed to fill the package name

(2) Configuration build environment

• Local.properties find the file in the library project relies add ndk tool position.

ndk.dir=/home/zhuxingchong/Android/Sdk/ndk-bundle

ndk position file-> project setting can be found below

• For compatibility with earlier versions ndk add file dependencies gradle.properties

android.useDepreCateNdk=true

Add file dependencies build.gradle ndk compiled modules and so files compiled file mk

apply plugin: 'com.android.library'

android {
    compileSdkVersion 28

    defaultConfig {
        minSdkVersion 23
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        ndk{
            moduleName "jni_blur"//生成so文件名
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild{
        ndkBuild{
            path "src/main/java/jni/Android.mk"//mk文件路径
        }
    }
}

(3) java file stated function

(4) generating a .h file

javah -d jni com.data.mylibrary.StackNative command generated .h files into the terminal mylibrary / src / main / java directory performed

After the completion of the command execution jni directory will be generated and the generated java directory under the directory

DETAILED .h file code is as follows

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_data_mylibrary_StackNative */

#ifndef _Included_com_data_mylibrary_StackNative
#define _Included_com_data_mylibrary_StackNative
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_data_mylibrary_StackNative
 * Method:    blurPixels
 * Signature: ([IIII)V
 */
JNIEXPORT void JNICALL Java_com_data_mylibrary_StackNative_blurPixels
  (JNIEnv *, jclass, jintArray, jint, jint, jint);

/*
 * Class:     com_data_mylibrary_StackNative
 * Method:    blurBitmap
 * Signature: (Ljava/lang/Object;I)V
 */
JNIEXPORT void JNICALL Java_com_data_mylibrary_StackNative_blurBitmap
  (JNIEnv *, jclass, jobject, jint);

#ifdef __cplusplus
}
#endif
#endif

(5) prepare specific logic .c or cpp file, and the file name can be changed .c suffix .h file as cpp or can be, because it is the picture a Gaussian blur processing code do more.

#include <android/log.h>
#include <android/bitmap.h>
#include "stackblur.h"

#define TAG "com_data_mylibrary_StackNative"
#define LOG_D(...) __android_log_print(ANDROID_LOG_DEBUG,TAG ,__VA_ARGS__)

JNIEXPORT void JNICALL
Java_com_data_mylibrary_StackNative_blurPixels
        (JNIEnv
         *env,
         jclass obj, jintArray
         arrIn,
         jint w, jint
         h,
         jint r
        ) {
    jint *pixels;
    // cpp:
    // pix = (env)->GetIntArrayElements(arrIn, 0);
    pixels = (*env)->GetIntArrayElements(env, arrIn, 0);
    if (pixels == NULL) {
        LOG_D("Input pixels isn't null.");
        return;
    }

    // Start
    pixels = blur_ARGB_8888(pixels, w, h, r);
    // End
    (*env)->ReleaseIntArrayElements(env, arrIn, pixels, 0);
}

JNIEXPORT void JNICALL
Java_com_data_mylibrary_StackNative_blurBitmap
        (JNIEnv
         *env,
         jclass obj, jobject
         bitmapIn,
         jint r
        ) {
    AndroidBitmapInfo infoIn;
    void *pixels;

    // Get image info
    if (AndroidBitmap_getInfo(env, bitmapIn, &infoIn) != ANDROID_BITMAP_RESULT_SUCCESS) {
        LOG_D("AndroidBitmap_getInfo failed!");
        return;
    }

    // Check image
    if (infoIn.format != ANDROID_BITMAP_FORMAT_RGBA_8888 &&
        infoIn.format != ANDROID_BITMAP_FORMAT_RGB_565) {
        LOG_D("Only support ANDROID_BITMAP_FORMAT_RGBA_8888 and ANDROID_BITMAP_FORMAT_RGB_565");
        return;
    }

    // Lock all images
    if (AndroidBitmap_lockPixels(env, bitmapIn, &pixels) != ANDROID_BITMAP_RESULT_SUCCESS) {
        LOG_D("AndroidBitmap_lockPixels failed!");
        return;
    }
    // height width
    int h = infoIn.height;
    int w = infoIn.width;

    // Start
    if (infoIn.format == ANDROID_BITMAP_FORMAT_RGBA_8888) {
        pixels = blur_ARGB_8888((int *) pixels, w, h, r);
    } else if (infoIn.format == ANDROID_BITMAP_FORMAT_RGB_565) {
        pixels = blur_RGB_565((short *) pixels, w, h, r);
    }
    // End
    // Unlocks everything
    AndroidBitmap_unlockPixels(env, bitmapIn);
}

(6) the preparation of documents mk

Android.mk

LOCAL_PATH		:= $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := jni_blur //生成so文件名
LOCAL_SRC_FILES := stackblur.c com_data_mylibrary_StackNative.c load.c //所有需要编译的c/cpp文件
LOCAL_LDLIBS    := -lm -llog -ljnigraphics

include $(BUILD_SHARED_LIBRARY)

Aplication.mk

APP_ABI		:= all
APP_PLATFORM:= android-23
APP_OPTIM	:= release

(7) compiled so aar file and package file

Click on android studio right side gradle-> mylibrary-> build-> build

Generate the appropriate library file location

(8) the response so aar file and copy the file to your project libs project

(9) arranged last in the dependent correlation which can be used build.gradle

 

note:

Generated header files when executed javah -d jni com.data.mylibrary.StackNative error

Error: Unable to determine Bitmap signature

public static native void blurBitmap(Bitmap bitmap, int r);改为

public static native void blurBitmap(Object bitmap, int r);

Last Source: Android-Jni_demo