D language function call with argument

Question

I am learning D and have mostly experience in C#. Specifically I am trying to use the Derelict3 Binding to SDL2. I have been able to get some basic functionality working just fine but I have become stumped on how to create an array argument for a specific call.

The library contains a call

SDL_RenderDrawLines(SDL_Renderer*, const(SDL_Point)*, int)  //Derelict3 Binding

And I have been unable to correctly form the argument for

const(SDL_Point)*

The SDL Documentation for this function states that this argument is an array of SDL_Point, but I am unclear how to create an appropriate array to pass to this function.

Here is an example of what I have at the moment:

void DrawShape(SDL_Renderer* renderer)
{
    SDL_Point a = { x:10, y:10};
    SDL_Point b = { x:500, y:500};

    const(SDL_Point[2]) points = [a,b];

    Uint8 q = 255;
    SDL_SetRenderDrawColor(renderer,q,q,q,q);
    SDL_RenderDrawLines(renderer,points,1);
}

And the compiler complains that I am not passing the correct type of argument for const(SDL_Point)* in points.

Error: function pointer SDL_RenderDrawLines (SDL_Renderer*, const(SDL_Point)*, int)
is not callable using argument types (SDL_Renderer*, const(SDL_Point[2u]), int)

I suspect this is a fundamental misunderstanding on my part so any help would be appreciated.

Answer 1

Arrays aren't implicitly castable to pointers in D. Instead, each array (both static and dynamic) has an intrinsic .ptr property that is a pointer to its first element.

Change your code to:

SDL_RenderDrawLines(renderer,points.ptr,1);

Answer 2

given that the call asks for a pointer and length, I feel it is safer to define you own wrapper:

SDL_RenderDrawLines(SDL_Renderer* rend, const SDL_Point[] points){
    SDL_RenderDrawLines(rend,points.ptr,points.length);
}

(why it isn't defined I don't know, any performance hit from the extra function call is just a -inline away from being resolved)