-
Notifications
You must be signed in to change notification settings - Fork 331
Windows Examples
require 'ffi' module Win VK_VOLUME_DOWN = 0xAE; VK_VOLUME_UP = 0xAF; VK_VOLUME_MUTE = 0xAD; KEYEVENTF_KEYUP = 2 extend FFI::Library ffi_lib 'user32' ffi_convention :stdcall attach_function :keybd_event, [ :uchar, :uchar, :int, :pointer ], :void # simulate pressing the mute key on the keyboard keybd_event(VK_VOLUME_MUTE, 0, 0, nil); keybd_event(VK_VOLUME_MUTE, 0, KEYEVENTF_KEYUP, nil); end
This example shows the common task of calling a native function with a pointer to a new struct, then using that same struct once it has been populated and returned by the native function.
This example shows how to use a native function that takes a callback specifying simple input parameters. The callback itself calls a native function which returns a string via its pointer to a character buffer parameter.
Note that the param you can pass “through” to the enum call is basically a pointer. An example of using this pointer for multiple objects can be found in the win32screenshot gem.
This example shows how to use Unicode text from Ruby with the Unicode version of the MessageBox
Windows API function.
There are three crucial points shown in the Ruby FFI code:
- The Windows API Unicode function version (
MessageBoxW
) is explicitly specified to FFI’sattach_function
. - Rather than using
:string
parameter types (as would normally be used with theMessageBoxA
ASCII version):buffer_in
parameter types are used for Unicode strings. In Ruby-FFI:string
means “null terminated C string” where UTF-16 is closer to a binary blob of data that can contain NULL bytes. NOTE: currently Ruby-FFI checks for NULL chars in:string
parameters to help avoid NULL byte poisoning attacks from outside string sources. - The Ruby string needs to be encoded to UTF-16LE and have a Unicode string terminator (double NULL)
This example shows how to interface with a native function that takes a pointer to a struct which contains an embedded union, both of which are populated before being provided to the native function.
The above FFI code takes a shortcut in the name of saving wiki page space. The actual Windows INPUT
struct contains an anonymous union member with MOUSEINPUT
, KEYBDINPUT
, and HARDWAREINPUT
members. As the MOUSEINPUT
struct is the largest of these members, we can get away with the hacky InputEvent
FFI union definition for example purposes.
TODO explain FFI syntax for embedded struct members which is opposite of typical C usage.
Bringing windows to the foreground is tricky, since no single call seems to always force it to the foreground.
http://betterlogic.com/roger/?p=2950 describes how.
Note that for windows’ core working you use a @ ffi_convention :stdcall@ but with normal DLL’s it appears you do not see here
- For all functions that take string arguments, the Windows API provides “short name” macros that expand to function names with a suffix indicating ASCII or Unicode. ASCII versions are suffixed with a “A”, and Unicode versions are suffixed with a “W”. For example, the Windows API
FindWindow
function gets defined as eitherFindWindowA
(ASCII) orFindWindowW
(Unicode).
- DWORD appears to be an :int (32 bits that is, so :int should work well)
- HWND appears to be a :pointer see this thread for why you should not actually read from the value it points to. You may as well just use a :long or :ulong.
- LPDWORD is a pointer (the P standing for pointer)
- LPARAM appears to be a long (hence the L)
- WPARAM appears to be a long (i.e. 64 bits on 64bit OS).
- BOOL is an :int
another list (the VB list at the bottom is especially helpful)
A few gems use FFI with the windows API.