Call COM object method from Go without CGo

Question

I have created a Direct3D9 wrapper in Go which uses CGo to interface with the COM objects in C.

I would like to get rid of the dependency on a C-compiler under Windows s

Answer 1

I asked the guys from go-ole, like @kostix suggested.

Here is the solution:

d3d9 doesn't have generally COM vtbl. for example, it doesn't have IDispatch interface. So you can't use go-ole for d3d9. But you can do it with writing all interface in go.

package main

import (
    "fmt"
    "log"
    "syscall"
    "unsafe"
)

const (
    D3D9_SDK_VERSION = 32
)

var (
    libd3d9             = syscall.NewLazyDLL("d3d9.dll")
    procDirect3DCreate9 = libd3d9.NewProc("Direct3DCreate9")
)

type IDirect3D struct {
    lpVtbl *IDirect3DVtbl
}

type IDirect3DVtbl struct {
    QueryInterface uintptr
    AddRef         uintptr
    Release        uintptr

    RegisterSoftwareDevice      uintptr
    GetAdapterCount             uintptr
    GetAdapterIdentifier        uintptr
    GetAdapterModeCount         uintptr
    EnumAdapterModes            uintptr
    GetAdapterDisplayMode       uintptr
    CheckDeviceType             uintptr
    CheckDeviceFormat           uintptr
    CheckDeviceMultiSampleType  uintptr
    CheckDepthStencilMatch      uintptr
    CheckDeviceFormatConversion uintptr
    GetDeviceCaps               uintptr
    GetAdapterMonitor           uintptr
    CreateDevice                uintptr
}

func (v *IDirect3D) AddRef() int32 {
    ret, _, _ := syscall.Syscall(
        v.lpVtbl.AddRef,
        1,
        uintptr(unsafe.Pointer(v)),
        0,
        0)
    return int32(ret)
}

func (v *IDirect3D) Release() int32 {
    ret, _, _ := syscall.Syscall(
        v.lpVtbl.Release,
        1,
        uintptr(unsafe.Pointer(v)),
        0,
        0)
    return int32(ret)
}

func (v *IDirect3D) GetAdapterCount() uint32 {
    ret, _, _ := syscall.Syscall(
        v.lpVtbl.GetAdapterCount,
        1,
        uintptr(unsafe.Pointer(v)),
        0,
        0)
    return uint32(ret)
}

func main() {
    v, r, err := procDirect3DCreate9.Call(uintptr(D3D9_SDK_VERSION))
    if r != 0 && err != nil {
        log.Fatal(err)
    }
    d3d := *((**IDirect3D)(unsafe.Pointer(&v)))

    d3d.AddRef()
    defer d3d.Release()

    fmt.Println(d3d.GetAdapterCount())
}

(c) mattn