Passing vectors from C++

[Edward Catchpole]

Is there a way to pass our C++ maths vector class to an ISPC export function as a short vector? It feels like there must be a way to do this, but the compiler denies it's possible, and the docs don't mention anything at all.

A simple example:

// test.ispc
export uniform float<3> AddVectors(uniform float<3> a, uniform float<3> b)
{
    return a + b;
}

// Vector.h
class Vector
{
public:
    float X;
    float Y;
    float Z;


    /* snip operators and helper functions */
};


// Test.cpp
Vector a = {1.f, 2.f, 3.f};
Vector b = {4.f, 5.f, 6.f};

Vector result = ispc::AddVectors(a, b);

This returns ispc errors complaining about the use of short vectors in the function signature:

<source>:42:25: Error: Illegal to return a "varying" or vector type from
        exported function "AddVectors"

export uniform float<3> AddVectors(uniform float<3> a, uniform float<3> b)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

<source>:42:53: Error: Vector-typed parameter "a" is illegal in an
        exported function.

export uniform float<3> AddVectors(uniform float<3> a, uniform float<3> b)
                                                    ^

<source>:42:73: Error: Vector-typed parameter "b" is illegal in an
        exported function.

export uniform float<3> AddVectors(uniform float<3> a, uniform float<3> b)

From what I can tell, my alternatives are to do some conversion manually, eg use uniform float[3], or uniform float*, or pass x/y/z parameters separately.

Am I missing another option?

[Dmitry Babokin]

Short vectors can't be passed by value in extern functions. You can pass them by pointer.

Also note, that short vectors definition as a struct in interface header has alignment attribute, so it's aligned at least to 16 bytes.

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