android-ndk-r21d 调用 FreeImage 实现图片格式转换

之前用opencv转换，感觉就是高射炮打蚊子，还只支持5种图像格式，连gif都不支持。使用FreeImage，它几乎支持所有的图片格式

ImageUtility.cpp

#include <jni.h>
#include <iostream>
using namespace std;
#include "freeimage.h"

extern "C" {

    unsigned char* ImageConvert(unsigned char* imageData, int imageDataSize, const char* format, int* returnSize)
    {
        FreeImage_Initialise();

            //read bytes to image object
            FIMEMORY * memory = FreeImage_OpenMemory(imageData, imageDataSize);
            FREE_IMAGE_FORMAT srcformat = FreeImage_GetFileTypeFromMemory(memory, 0);
            FIBITMAP *bitmap = FreeImage_LoadFromMemory(srcformat, memory, 0);
            FreeImage_CloseMemory(memory);

            //convert image object type
            FIMEMORY* hmem = FreeImage_OpenMemory();
            FreeImage_SaveToMemory(FreeImage_GetFIFFromFilename(format), bitmap, hmem, 0);

            //save image object type to bytes
            FreeImage_SeekMemory(hmem, 0, SEEK_END);
            long bufferSize = FreeImage_TellMemory(hmem);
            unsigned char* buffer = new unsigned char[bufferSize];
            unsigned int actualReadCount = bufferSize;
            FreeImage_SeekMemory(hmem, 0, SEEK_SET);
            FreeImage_ReadMemory(buffer, bufferSize, actualReadCount, hmem);
            FreeImage_CloseMemory(hmem);

            FreeImage_DeInitialise();

            *returnSize = bufferSize;
            return buffer;
    }
}

Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE := FreeImage
LOCAL_SRC_FILES := libs/$(TARGET_ARCH_ABI)/libFreeImage.a
include $(PREBUILT_STATIC_LIBRARY)

include $(CLEAR_VARS)
LOCAL_MODULE     := ImageUtility
LOCAL_SRC_FILES := ImageUtility.cpp
LOCAL_STATIC_LIBRARIES  := libFreeImage
LOCAL_SHORT_COMMANDS    := true
include $(BUILD_SHARED_LIBRARY)

Application.mk

ADDITIONAL_FLAGS := -O3 -fopenmp -DANDROID -Wno-c++11-narrowing
APP_CFLAGS += $(ADDITIONAL_FLAGS)
APP_CONLYFLAGS += -std=c11
APP_CPPFLAGS += $(ADDITIONAL_FLAGS) -std=c++11 -fexceptions -frtti
APP_PLATFORM := android-21
APP_STL   := c++_static
APP_ABI   := all
APP_OPTIM := release
APP_SHORT_COMMANDS := true

调用命令 ndk-build 生成 .so
Android java 调用核心代码：

public interface ImageUtility extends Library
{
    public Pointer ImageConvert(Pointer data, int dataSize, String format , Pointer resultSize);
}

...
//get image bytes async from internet
byte[] data = (byte[]) result;

ImageUtility imageUtility = (ImageUtility) Native.loadLibrary("ImageUtility", ImageUtility.class);
Pointer ptr = new Memory(data.length);
ptr.write(0, data, 0, data.length);
Pointer returnSize = new Memory(4);
Pointer imagePointer = imageUtility.ImageConvert(ptr, data.length, ".gif" , returnSize);
byte[] imageBytes = imagePointer.getByteArray(0, returnSize.getInt(0));
Bitmap bitmap = BitmapFactory.decodeByteArray(imageBytes,0, imageBytes.length, new BitmapFactory.Options());

...

其中用到了jna调用so动态链接库