FSharpPointers

module Gists.FSharp.SilkNetSdl

open System.Runtime.CompilerServices
open Gists.CSharp
open Microsoft.FSharp.NativeInterop
open Silk.NET.SDL
open Silk.NET.Maths

let fillRect (api: Sdl) (screen: nativeptr<Surface>) color =
    let nullref = &Unsafe.NullRef<Rectangle<int>>()
    api.FillRect(screen, &nullref, color) // picks byref overload

//public static unsafe class NativePtr
//{
//    public static T* toValuePtr<T>(void* ptr)
//        where T: unmanaged
//        => (T*) ptr;
//}

let fillRect2 (api: Sdl) (screen: nativeptr<Surface>) color =
    let nullref = &Unsafe.NullRef<Rectangle<int>>()
    let ptr2 = NativePtr.toValuePtr<Rectangle<int>> (Unsafe.AsPointer &nullref)
    api.FillRect(screen, ptr2, color)

//public static T* zero<T>()
//        where T: unmanaged
//        => (T*) IntPtr.Zero;

let fillRect3 (api: Sdl) (screen: nativeptr<Surface>) color =
    let ptr = NativePtr.zero<Rectangle<int>>()
    api.FillRect(screen, ptr, color)

// define C# to F# helpers if needed
module NativePtr =
    let zeroFSharp<'a when 'a: (new: unit -> 'a) and 'a : struct and 'a :> System.ValueType> = NativePtr.zero<'a>()

let fillRect4 (api: Sdl) (screen: nativeptr<Surface>) color =
    let ptr = NativePtr.zeroFSharp<Rectangle<int>>
    api.FillRect(screen, ptr, color)