Mimicking a keyboard from within a program?

I'm trying to make a "vision joystick" using OpenCV. My plan is to have motion-triggered buttons which the computer would recognize as keyboard input instead. So, for example, if the user triggered the space button onscreen, a space might appear in a text editor, or a characte开发者_JAVA技巧r may jump in a game (we're really trying to make this work for emulators). Is there any simple way to trigger these inputs?

I believe the method will be highly platform-dependent. On Windows, for instance, you should use the SendInput function.