圖形影象實踐

• android全平臺編譯libjpeg-turbo並基於ANativeWindow載入JPEG圖片
• android全平臺編譯libpng並基於ANativeWindow載入PNG圖片

環境配置

作業系統：ubuntu 16.05
ndk版本：android-ndk-r16b
libpng版本：libpng-1.6.35
zlib版本：zlib-1.2.11

進入libpng-1.6.35/scripts目錄，將pnglibconf.h.prebuilt複製到libpng-1.6.35目錄下，並重命名為pnglibconf.h

開始執行ndk-build

載入PNG圖片

新建native-png工程

新建NativePngLoader類

package com.onzhou.graphic.png;

import android.view.Surface;

public class NativePngLoader {

    static {
        System.loadLibrary("native-png");
    }

    public native void loadPNGImage(String imagePath, Surface surface);


}

新建native_png.cpp的native實現類

#include <jni.h>
#include <stdio.h>
#include <time.h>
#include <android/native_window.h>
#include <android/native_window_jni.h>

#include "native_png.h"
#include "png.h"
#include "zlib.h"
#include <malloc.h>
#include <string.h>

#ifdef ANDROID

#include <
 
android/log.h>


#define LOG_TAG    "NativePNG"
#define LOGE(format, ...)  __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, format, ##__VA_ARGS__)
#define LOGI(format, ...)  __android_log_print(ANDROID_LOG_INFO,  LOG_TAG, format, ##__VA_ARGS__)
#else
#define LOGE(format, ...)  printf(LOG_TAG format "\n", ##__VA_ARGS__)
#define LOGI(format, ...)  printf(LOG_TAG format "\n", ##__VA_ARGS__)
#endif


/**
 * 動態註冊
 */
JNINativeMethod methods[] = {
        {"loadPNGImage", "(Ljava/lang/String;Landroid/view/Surface;)V", (void *) loadPNGImage}
};

/**
 * 動態註冊
 * @param env
 * @return
 */
jint registerNativeMethod(JNIEnv *env) {
    jclass cl = env->FindClass("com/onzhou/graphic/png/NativePngLoader");
    if ((env->RegisterNatives(cl, methods, sizeof(methods) / sizeof(methods[0]))) < 0) {
        return -1;
    }
    return 0;
}

/**
 * 載入預設回撥
 * @param vm
 * @param reserved
 * @return
 */
jint JNI_OnLoad(JavaVM *vm, void *reserved) {
    JNIEnv *env = NULL;
    if (vm->GetEnv((void **) &env, JNI_VERSION_1_6) != JNI_OK) {
        return -1;
    }
    //註冊方法
    if (registerNativeMethod(env) != JNI_OK) {
        return -1;
    }
    return JNI_VERSION_1_6;
}

void ThrowException(JNIEnv *env, const char *exception, const char *message) {
    jclass clazz = env->FindClass(exception);
    if (NULL != clazz) {
        env->ThrowNew(clazz, message);
    }
}

void drawPNG(const char *name, ANativeWindow_Buffer &nwBuffer) {
    FILE *file = fopen(name, "rb");

    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);
    if (png_ptr == NULL) {
        fclose(file);
        return;
    }
    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (info_ptr == NULL) {
        fclose(file);
        png_destroy_write_struct(&png_ptr, NULL);
        return;
    }
    if (setjmp(png_jmpbuf(png_ptr))) {
        fclose(file);
        png_destroy_write_struct(&png_ptr, &info_ptr);
        return;
    }
    //開始讀檔案
    png_init_io(png_ptr, file);

    png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0);

    //獲取檔案的寬高色深
    int m_width = png_get_image_width(png_ptr, info_ptr);
    int m_height = png_get_image_height(png_ptr, info_ptr);

    //獲取影象的色彩型別
    int color_type = png_get_color_type(png_ptr, info_ptr);

    LOGI("width=%d,height=%d,color_type=%d", m_width, m_height, color_type);

    // row_pointers內部存放的就是RGBA資料了
    png_bytep *row_pointers = png_get_rows(png_ptr, info_ptr);

    switch (color_type) {
        case PNG_COLOR_TYPE_RGB_ALPHA:
            //RGBA32
            break;
        case PNG_COLOR_TYPE_RGB: {
            //RGB24,沒有A通道,就要3位3位的讀
            uint32_t *line = (uint32_t *) nwBuffer.bits;
            for (int row = 0; row < m_height; row++) {
                for (int column = 0; column < m_width; column++) {
                    //儲存順序為BGR,BGR,BGR......
                    line[column] = ((uint32_t) row_pointers[row][3 * column + 2]) << 16
                                   | ((uint32_t) row_pointers[row][3 * column + 1]) << 8
                                   | (uint32_t) row_pointers[row][3 * column];
                }
                line = line + nwBuffer.stride;
            }
        }
    }
    png_destroy_read_struct(&png_ptr, &info_ptr, 0);
    fclose(file);
}


void loadPNGImage(JNIEnv *env, jobject obj, jstring jpegPath, jobject surface) {

    const char *path = env->GetStringUTFChars(jpegPath, 0);
    //獲取目標surface
    ANativeWindow *window = ANativeWindow_fromSurface(env, surface);
    if (NULL == window) {
        ThrowException(env, "java/lang/RuntimeException", "unable to get native window");
        return;
    }
    //預設的是RGB_565
    int32_t result = ANativeWindow_setBuffersGeometry(window, 0, 0, WINDOW_FORMAT_RGBA_8888);
    if (result < 0) {
        ThrowException(env, "java/lang/RuntimeException", "unable to set buffers geometry");
        //釋放視窗
        ANativeWindow_release(window);
        window = NULL;
        return;
    }
    ANativeWindow_acquire(window);

    ANativeWindow_Buffer buffer;
    //鎖定視窗的繪圖表面
    if (ANativeWindow_lock(window, &buffer, NULL) < 0) {
        ThrowException(env, "java/lang/RuntimeException", "unable to lock native window");
        //釋放視窗
        ANativeWindow_release(window);
        window = NULL;
        return;
    }

    //繪製PNG圖片
    drawPNG(path, buffer);

    //解鎖視窗的繪圖表面
    if (ANativeWindow_unlockAndPost(window) < 0) {
        ThrowException(env, "java/lang/RuntimeException",
                       "unable to unlock and post to native window");
    }

    env->ReleaseStringUTFChars(jpegPath, path);
    //釋放
    ANativeWindow_release(window);
}

注意：上面的過程其實也比較簡單，但是跟讀取JPEG圖片區別在於要根據色彩來區分RGB和RGBA

• 先通過ANativeWindow_fromSurface獲取對應的視窗
• 通過libpng載入對應的png圖片，解碼成RGBA資料
• 將最終的RGBA資料寫入到buffer中去，完成繪製

編寫cmake的配置檔案CMakeLists.txt

cmake_minimum_required(VERSION 3.4.1)

##官方標準配置
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -fno-rtti -fno-exceptions -Wall")

add_library(native-png
           SHARED
           src/main/cpp/native_png.cpp)

add_library(png
           SHARED
           IMPORTED)

set_target_properties(png
                    PROPERTIES IMPORTED_LOCATION
                    ${CMAKE_SOURCE_DIR}/libs/${ANDROID_ABI}/libpng.so
                    )

add_library(zip
           SHARED
           IMPORTED)

set_target_properties(zip
                    PROPERTIES IMPORTED_LOCATION
                    ${CMAKE_SOURCE_DIR}/libs/${ANDROID_ABI}/libz.so
                    )

#標頭檔案
include_directories(${CMAKE_SOURCE_DIR}/src/main/cpp/include_png)
include_directories(${CMAKE_SOURCE_DIR}/src/main/cpp/include_zlib)

target_link_libraries(native-png
            png
            zip
            android
            jnigraphics
            log)

在啟動的目標Activity中載入我們指定的JPEG圖片

mSurfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        NativeImageLoader nativeImageLoader = new NativeImageLoader();
        File file = new File(getExternalFilesDir(null), "input.jpeg");
        nativeImageLoader.loadJPEGImage(file.getAbsolutePath(), holder.getSurface());
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {

    }
});

可以看到如下輸出：

專案地址：native-png
https://github.com/byhook/graphic4android

參考：
https://blog.csdn.net/talkxin/article/details/50968313