How to allocate the LUT to use on ScriptIntrinsic3DLUT?

working with RenderScript, I'm trying to use the ScriptIntrinsic3DLUT (http://developer.android.com/reference/android/renderscript/ScriptIntrinsic3DLUT.html)

In general this scrip works just like any other renderscript

create RS context
create script with this context
create input and output allocations
set script parameters
call the kernel

may problem is on the set script parameters step, from the docs I should call script.setLUT (Allocation lut), but what is the appropriate way of generating/setting values for this allocation?

sample of the code I have is:

// create RS context
RenderScript rs = RenderScript.create(context);

// create output bitmap
Bitmap bitmapOut = Bitmap.createBitmap(bitmapIn.getWidth(), bitmapIn.getHeight(), bitmapIn.getConfig());

// create bitmap allocations
Allocation allocIn = Allocation.createFromBitmap(rs, bitmapIn);
Allocation allocOut = Allocation.createFromBitmap(rs, bitmapOut);

// create script
ScriptIntrinsic3DLUT script = ScriptIntrinsic3DLUT.create(rs, Element.U8_4(rs));

// set 3D LUT for the script
how to create the `Allocation lut` ??
script.setLUT(lut);

// process the script
script.forEach(allocIn, allocOut);

// copy result to bitmap output
allocOut.copyTo(bitmapOut);

My question is similar to How to use ScriptIntrinsic3DLUT with a .cube file?

but it is not the same. I do not care about the cube file. I can create the LUT from array of bytes, ints, matrix, whatever. I just want to know how-to/where-to place those bytes inside the allocation. What's the appropriate formatting for this allocation?

Solution

I found an example on the web here: https://android.googlesource.com/platform/frameworks/rs/+/master/java/tests/ImageProcessing/src/com/android/rs/image/ColorCube.java

This creates a 3D LUT that doesn't modify the actual color values. Good example though how it could work.

private ScriptIntrinsic3DLUT mIntrinsic;
private void initCube() {
        final int sx = 32;
        final int sy = 32;
        final int sz = 16;
        Type.Builder tb = new Type.Builder(mRS, Element.U8_4(mRS));
        tb.setX(sx);
        tb.setY(sy);
        tb.setZ(sz);
        Type t = tb.create();
        mCube = Allocation.createTyped(mRS, t);
        int dat[] = new int[sx * sy * sz];
        for (int z = 0; z < sz; z++) {
            for (int y = 0; y < sy; y++) {
                for (int x = 0; x < sx; x++ ) {
                    int v = 0xff000000;
                    v |= (0xff * x / (sx - 1));
                    v |= (0xff * y / (sy - 1)) << 8;
                    v |= (0xff * z / (sz - 1)) << 16;
                    dat[z*sy*sx + y*sx + x] = v;
                }
            }
        }
        mCube.copyFromUnchecked(dat);
    }

and then use it like so

mIntrinsic.setLUT(mCube);

If anyone can help with parsing a .cube file and fitting into this i would be very grateful.