Using winapi in Rust to get a bitmap from a window - winapi

Question

.. Hi, I have this code :
#[cfg(windows)] extern crate winapi;
use winapi::um::winuser::{FindWindowW, GetClientRect, GetWindowDC, GetDC, ReleaseDC};
use winapi::um::wingdi::{CreateBitmap, CreateCompatibleBitmap, CreateCompatibleDC, SelectObject, GetObjectW, SaveDC, DeleteDC, DeleteObject};
use std::ptr::null_mut;
use std::mem::zeroed;
use std::ffi::OsStr;
use std::iter::once;
use std::os::windows::ffi::OsStrExt;
#[cfg(windows)]
fn find_window(name: &str) {
let window: Vec<u16> = OsStr::new(name).encode_wide().chain(once(0)).collect();
let hwnd = unsafe { FindWindowW(null_mut(), window.as_ptr()) };
if hwnd != null_mut() {
println!("Window found");
let mut my_rect = unsafe { zeroed::<winapi::shared::windef::RECT>() };
let _client_rect = unsafe { GetClientRect(hwnd, &mut my_rect) };
let w = my_rect.right - my_rect.left;
let h = my_rect.bottom - my_rect.top;
let hwnd_dc = unsafe { GetWindowDC(hwnd) };
let mem_dc = unsafe { CreateCompatibleDC(hwnd_dc) };
let bmp = unsafe { CreateCompatibleBitmap(mem_dc, w, h) };
//SelectObject(mem_dc, bmp); <== Problem is here
//DeleteObject(bmp); <== Same problem here
unsafe { DeleteDC(mem_dc) };
unsafe { ReleaseDC(hwnd, hwnd_dc) };
}
else {
println!("Window not found");
}
}
fn main() {
find_window("Firefox"); // just for test
}
If I cargo run this, I get :
SelectObject(mem_dc, bmp);
| ^^^ expected enum `std::ffi::c_void`, found enum `winapi::shared::windef::HBITMAP__`
So I get it, it doesn't want that bitmap pointer, but in the win32 documentation, it says that this function (SelectObject) accepts a Device Context (mem_dc) and an object created by some function like CreateCompatibleBitmap.
https://learn.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-selectobject
The binding in Rust accepts the two same arguments but it seems to want that std::ffi::c_void but looking a the Rust doc, I don't get what it is exactly.
Can you help me finding what's wrong ? Thanks.

Answer 1

Add:
use winapi::shared::windef::{HBITMAP, HBITMAP__, HGDIOBJ, HWND, POINT, RECT, SIZE};
...
unsafe {SelectObject(mem_dc, bmp as HGDIOBJ)};
unsafe {DeleteObject(bmp as HGDIOBJ)};