Make a counter for transparent pixels from a Bitmap in Renderscript

Question

My problem is to get the amount of transparent parts/pixels in an image which is changed because of an OnTouchEvent by the user.

So I would like to transform the following java code into renderscript code:

public int transparentPixels(){  

    int amount = 0;

    for(int x = 0; x < sourceBitmap.getWidth(); x++){
        for(int y = 0; y < sourceBitmap.getHeight(); y++){

            if(sourceBitmap.getPixel(x,y) == Color.TRANSPARENT){

                amount += 1;

            }

        }
    }

    return amount;
}

Please add code snippets from the rs and java file.

Thanks in advance!

Answer 1

Reference: RenderScript Docs and rsAtomicInc .

Here is my sample code. Refer to winklerrr 's solution here .

RSexample.rs

use in->a to retrive alpha and check its value.

#pragma version(1)
#pragma rs java_package_name(RS)
#pragma rs_fp_relaxed

int32_t count = 0;
rs_allocation rsAllocationCount;

void countPixels(uchar4* in, uint x, uint y) {
  if(in->a==0)rsAtomicInc(&count);
  rsSetElementAt_int(rsAllocationCount, count, 0);
}

RSContext.java

acts as context between MainActivity.java and RSexample.rs.

public void init(Context context) {
    rs = RenderScript.create(context);
    scriptC_RS = new ScriptC_RSexample(rs);
}
public void setup(int w, int h){
    rgb888Type = Type.createXY(rs, Element.RGBA_8888(rs), w, h);
    allocIn = Allocation.createTyped(rs, rgb888Type, Allocation.USAGE_SCRIPT);
    allocCount = Allocation.createTyped(rs, Type.createX(rs, Element.I32(rs), 1));
}
public void addPic(Bitmap bitmap) {
    allocIn = Allocation.createFromBitmap(rs, bitmap);
}
public int getCount(){
    scriptC_RS.set_rsAllocationCount(allocCount);
    scriptC_RS.forEach_countPixels(allocIn);
    int[] count = new int[1];
    allocIn.syncAll(Allocation.USAGE_SCRIPT);
    allocCount.copyTo(count);
    return count[0];
}

MainActivity.java

RSContext rsContext = new RSContext();
rsContext.init(this);
rsContext.setup(bitmap.getWidth(), bitmap.getHeight());
rsContext.addPic(bitmap);
int transparentPixel = rsContext.getCount();