Instant Rimshot

Posted: 2009-06-20 Last updated: 2012-04-18

It's been a while since I've written anything here, I've been working on my master project like crazy, have a 6 month old baby and so haven't had much time for programming pet projects. Tonight I spent a half hour making perhaps the most useless application I'll ever make. It's based on the single-serving website http://instantrimshot.com which only has one huge red button, if you press it a rimshot sound is played. I thought it might be fun to have that available as a keyboard shortcut in windows, and then I started wondering how it could be done in C#.

The only way to get a global keyboard working in .NET is by calling into the Win32 API. To register a global hotkey there is the aptly named function RegisterHotKey. That requires you to have a window handle however, and I wanted to make the application as simple as possible, so I used a lower level API call, SetWindowsHookEx which lets you get notified of all keyboard activity on the system. I then check what keys are pressed and when the combination Ctrl+Shift+I is pressed the sound is played. There is only one way to exit the app, and that is by pressing the keyboard combination Ctrl+Shift+Alt+I, that cleans up the hook before exiting. So, the code is shown below, you can download the source or just download the program itself. Enjoy!


using System;
using System.IO;
using System.Media;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Windows.Forms;

class InstantRimshot {

	const int WH_KEYBOARD_LL = 13;
	const int WM_KEYDOWN = 0x100;

	delegate int Hook(int code, IntPtr wParam, IntPtr lParam);

	[DllImport("user32.dll")]
	static extern IntPtr SetWindowsHookEx(int code,
										  Hook func,
										  IntPtr hInstance,
										  int threadID);

	[DllImport("user32.dll")]
	static extern int UnhookWindowsHookEx(IntPtr hookHandle);

	[DllImport("user32.dll")]
	static extern int CallNextHookEx(IntPtr hhook,
									 int code,
									 IntPtr wParam,
									 IntPtr lParam);

	static bool IsPressed(Keys check) {
		return ((Control.ModifierKeys & check) == check);
	}

	static void Main() {

		Stream sound = Assembly.GetExecutingAssembly()
			.GetManifestResourceStream("InstantRimshot.rimshot.wav");
		SoundPlayer player = new SoundPlayer(sound);
		player.Load();
		IntPtr hookHandle = IntPtr.Zero;
		hookHandle = SetWindowsHookEx(WH_KEYBOARD_LL,
			delegate(int code, IntPtr wParam, IntPtr lParam) {
				if (code >= 0 && wParam == (IntPtr) WM_KEYDOWN) {
					Keys vkCode = (Keys)Marshal.ReadInt32(lParam);
					if (Keys.I == vkCode
					&& IsPressed(Keys.Control)
					&& IsPressed(Keys.Shift)) {
						if (IsPressed(Keys.Alt)) {
							UnhookWindowsHookEx(hookHandle);
							Application.Exit();
							return CallNextHookEx(hookHandle, code,
												  wParam, lParam);
						} else {
							player.Play();
						}
					}
				}
				return CallNextHookEx(hookHandle, code, wParam, lParam);
			}, IntPtr.Zero, 0);
		Application.Run();
	}

}