Function signature for __attribute__(kernel) function and usage of "OutAllocation"

Question

I intend to process RGB data through RenderScript.

For this I've created Allocations in Java and passing them to RS Kernel function as below:

uchar3 __attribute__((kernel)) invert(uchar3 v_in, uint32_t v_out) {
v_in.r = ...;
v_in.g = ...;
v_in.b = ...;
}

However ideally I would like to work on v_out in similar way i.e. setting values for v_out.r, v_out.g and v_out.b. Currently I can not do this with uint32_t v_out.

Now if I define the above RS kernel as:

uchar3 __attribute__((kernel)) invert(uchar3 v_in, uchar3 v_out) {
...
}

I get below compile time error: error: Unexpected kernel invert() parameter 'v_out' of type 'uchar3 *'

Please suggest how to resolve this.

Compile time:

error: Unexpected kernel invert() parameter 'v_out' of type 'uchar3 *'

Answer 1

you should be defining this as

uchar3 __attribute__((kernel)) invert(uchar3 in);

that function will then be reflected as ScriptC_.forEach_invert(Allocation in, Allocation out). each element in in will be passed to invert, and each value returned from invert will be written to the corresponding location in out.

Answer 2

Define your own local variable of uchar3 type and then populate it before returning it:

uchar3 __attribute__((kernel)) invert(uchar3 in) {
    uchar3 out;
    out.r = ...
    out.g = ...
    out.b = ...
    return out;
}

The compiler is clever enough to notice what you are doing, so there won't be additional copies made of the output items.