Example of creating a window with a PaintDc context and drawing to it using a brush. Probably incorrect.

paint.rs

// Copyright 2015 The Rust-Windows Project Developers. See the
// COPYRIGHT file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#![feature(libc)]

extern crate libc;

extern crate winapi;
#[macro_use]
extern crate rust_windows as windows;
extern crate gdi32;
extern crate user32;

use libc::c_int;
use std::{mem, ptr};

use winapi::{HWND, HRGN, HBRUSH, CREATESTRUCTW, UINT};

use windows::main_window_loop;
use windows::instance::Instance;
use windows::resource::*;
use windows::window::{WindowImpl, Window, WndClass, WindowParams};
use windows::window::{OnCreate, OnDestroy, OnPaint};
use windows::window;
use windows::gdi::PaintDc;

struct MainFrame {
    pub win: Window,
    title: String,    
}

pub const CW_USEDEFAULT: c_int = 0x80000000u32 as c_int;

pub const GA_PARENT: UINT = 1;
pub const GA_ROOT: UINT = 2;
pub const GA_ROOTOWNER: UINT = 3;

wnd_proc!(MainFrame, win, WM_CREATE, WM_DESTROY, WM_PAINT);

impl OnCreate for MainFrame {
    fn on_create(&self, _cs: &CREATESTRUCTW) -> bool {
        let params = WindowParams {
            window_name: "Learn to Program Windows".to_string(),
            style: window::WS_OVERLAPPEDWINDOW,
            x: CW_USEDEFAULT as isize,
            y: CW_USEDEFAULT as isize,
            width: CW_USEDEFAULT as isize,
            height: CW_USEDEFAULT as isize,
            parent: self.win,
            menu: ptr::null_mut(),
            ex_style: 0,
        };
        let sample_window = Window::new(Instance::main_instance(), None, "Sample Window Class", &params);
        match sample_window {
            None => false,
            Some(e) => true,
        }
    }
}

impl OnDestroy for MainFrame {}

impl OnPaint for MainFrame {
    fn on_paint(&self) {
        let pdc = PaintDc::new(self).expect("Paint DC");
        let client_rect = self.win.client_rect().unwrap();
        let hrgn: HRGN = unsafe {
            gdi32::CreateRectRgnIndirect(&client_rect)
        };
        let hbrush: HBRUSH = unsafe {
            gdi32::CreateSolidBrush(0x008f1e35)
        };
        unsafe {
            gdi32::FillRgn(pdc.dc.raw(), hrgn, hbrush);
        }
    }
}

impl MainFrame {
    fn new(instance: Instance, title: String) -> Option<Window> {
        let wnd_class = WndClass {
            classname: "Sample Window Class".to_string(),
            style: 0x0001 | 0x0002, // CS_HREDRAW | CS_VREDRAW
            icon: None,
            icon_small: None,
            cursor: Image::load_cursor_resource(32512), // hourglass
            background: (5 + 1) as HBRUSH,
            menu: MenuResource::MenuId(0),
            cls_extra: 0,
            wnd_extra: 0,
        };
        let res = wnd_class.register(instance);
        if !res {
            return None;
        }

        let wproc = Box::new(MainFrame {
            win: Window::null(),
            title: title.clone(),            
        });

        let win_params = WindowParams {
            window_name: title,
            style: window::WS_OVERLAPPEDWINDOW,
            x: CW_USEDEFAULT as isize,
            y: CW_USEDEFAULT as isize,
            width: CW_USEDEFAULT as isize,
            height: CW_USEDEFAULT as isize,
            parent: Window::null(),
            menu: ptr::null_mut(),
            ex_style: 0,
        };

        Window::new(instance, Some(wproc as Box<WindowImpl + 'static>),
                    &wnd_class.classname[..], &win_params)
    }
}

fn main() {
    let instance = Instance::main_instance();
    let main = MainFrame::new(instance, "Learn to Program Windows".to_string());
    let main = main.unwrap();
    main.show(1);
    main.update();

    let exit_code = main_window_loop();
    std::process::exit(exit_code as i32);
}