CODEWITHSUNDEEP
androidc++candroid-ndkjava-native-interface
NEB
NEB

Reputation: 734

Creating a new Bitmap with Pixel Data in JNI?

I've the below code to create a BitMap (Just a Black / Gray Image) in the JNI with 'ARGB_8888' configuration. But when I dump the content of the Bitmap in the Java code, I'm able to see only the configurations, but not the Pixel Data in the Bitmap.

JNI Code

// Image Details
int imgWidth = 128;
int imgHeight = 128;
int numPix = imgWidth * imgHeight;

// Creaing Bitmap Config Class
jclass bmpCfgCls = env->FindClass("android/graphics/Bitmap$Config");
jmethodID bmpClsValueOfMid = env->GetStaticMethodID(bmpCfgCls, "valueOf", "(Ljava/lang/String;)Landroid/graphics/Bitmap$Config;");
jobject jBmpCfg = env->CallStaticObjectMethod(bmpCfgCls, bmpClsValueOfMid, env->NewStringUTF("ARGB_8888"));

// Creating a Bitmap Class
jclass bmpCls = env->FindClass("android/graphics/Bitmap");
jmethodID createBitmapMid = env->GetStaticMethodID(bmpCls, "createBitmap", "(IILandroid/graphics/Bitmap$Config;)Landroid/graphics/Bitmap;");
jBmpObj = env->CallStaticObjectMethod(bmpCls, createBitmapMid, imgWidth, imgHeight, jBmpCfg);

// Creating Pixel Data
int triplicateLen = numPix * 4;
char *tripPixData = (char*)malloc(triplicateLen);
for (int lc = 0; lc < triplicateLen; lc++)
{ 
    // Gray / Black Image
    if (0 == (lc%4))
        tripPixData[lc] = 0x7F; // Alpha
    else
        tripPixData[lc] = 0x00; // RGB
}

// Setting Pixels in Bitmap
jByteArr = env->NewByteArray(triplicateLen);
env->SetByteArrayRegion(jByteArr, 0, triplicateLen, (jbyte*)tripPixData);
jmethodID setPixelsMid = env->GetMethodID(bmpCls, "setPixels", "([IIIIIII)V");
env->CallVoidMethod(jBmpObj, setPixelsMid, (jintArray)jByteArr, 0, imgWidth, 0, 0, imgWidth, imgHeight);

free(tripPixData);

// Return BitMap Object
return jBmpObj;

In JAVA (Output)

// Checking the Configuration / Image Details
jBmpObj.getWidth() - 128
jBmpObj.getHeight() - 128
jBmpObj.getRowBytes() - 512
jBmpObj.getConfig() - ARGB 8888

// Getting Pixel Data
imgPixs = new int[jBmpObj.getWidth() * jBmpObj.getHeight()];
jBmpObj.getPixels(imgPixs, 0, jBmpObj.getWidth(), 0, 0, jBmpObj.getWidth(), jBmpObj.getHeight());

// Running a Loop on the imgPixs
imgPixs[<0 - imgPixs.lenght>] - 0 (Every Pixel Data)

I used the same concept to create a Bitmap in the Java Code, and it works fine (Even I'm able to see the image). But I want the logic to be in the JNI part and not in Java Code. So I tried the above logic and it failed in setting the Pixel Data.

Any input in fixing this issue will be really helpful,..

Upvotes: 2

Views: 7333

Answers (3)

Evgeni Roitburg
Evgeni Roitburg

Reputation: 2097

Full working example:

jclass bitmapConfig = jniEnv->FindClass("android/graphics/Bitmap$Config");
    jfieldID rgba8888FieldID = jniEnv->GetStaticFieldID(bitmapConfig, "ARGB_8888", "Landroid/graphics/Bitmap$Config;");
    jobject rgba8888Obj = jniEnv->GetStaticObjectField(bitmapConfig, rgba8888FieldID);

    jclass bitmapClass = jniEnv->FindClass("android/graphics/Bitmap");
    jmethodID createBitmapMethodID = jniEnv->GetStaticMethodID(bitmapClass,"createBitmap", "(IILandroid/graphics/Bitmap$Config;)Landroid/graphics/Bitmap;");
    jobject bitmapObj = jniEnv->CallStaticObjectMethod(bitmapClass, createBitmapMethodID, _width, _height, rgba8888Obj);

    jintArray pixels = jniEnv->NewIntArray(_width * _height);
    for (int i = 0; i < _width * _height; i++)
    {
        unsigned char red = bitmap[i*4];
        unsigned char green = bitmap[i*4 + 1];
        unsigned char blue = bitmap[i*4 + 2];
        unsigned char alpha = bitmap[i*4 + 3];
        int currentPixel = (alpha << 24) | (red << 16) | (green << 8) | (blue);
        jniEnv->SetIntArrayRegion(pixels, i, 1, &currentPixel);
    }

    jmethodID setPixelsMid = jniEnv->GetMethodID(bitmapClass, "setPixels", "([IIIIIII)V");
    jniEnv->CallVoidMethod(bitmapObj, setPixelsMid, pixels, 0, _width, 0, 0, _width, _height);

where bitmap is unsigned char*.

Upvotes: 11

user3714144
user3714144

Reputation: 159

IN Android each pixel represented as 0xFFFFFFFF ie ARGB.
0xFF referes most significamt 8 bits of given data.
From your snippet, where you are getting soure image data? But i have solved this issue
by using following code base.i hope this ll help you.

// Creating Pixel Data

unsigned char* rawData = //your raw data

**Note**: here you have get each r,g & b component as 8 bit data //If it is rgb image,if it             
is monochrome you can use raw data

int triplicateLen = imgheight * imgwidth;
int *tripPixData = (int*) malloc(triplicateLen * sizeof(int));

if(rgb){
       for (int lc = 0; lc < triplicateLen ; lc++){
            tripPixData [lc] = (0xFF << 24) | (r[lc] << 16) | (g[lc] << 8) | b[lc]; 
       }
 }else{
      for (int lc = 0; lc < triplicateLen ; lc++){
            tripPixData [lc] = (0xFF << 24) | (rawData [lc] << 16) | (rawData [lc] << 8) | rawData [lc];    
       }
 }

Upvotes: 0

Alex Cohn
Alex Cohn

Reputation: 57173

You cannot cast byte[] to int[] in Java, therefore you cannot cast it in JNI. But you can cast char* to int*, so you can simply use your tripPixData to fill a new jjintArray.

Upvotes: 0

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