Input Handling 2.0

[alanjfs]

A discussion topic regarding the way input is managed in the example application and how it can be improved.

• Download for Windows

Goal

Translate input from any device - e.g. mouse, Wacom, Wii or XBox controller, eye tracker - to generic input, independent of device origin, with support for two or more devices operating in parallel, such as two mice.

Motivation

The coloured squares in the example application are currently controlled by click + dragging with your mouse. It should also work with a touch screen, courtesy of GLFW translating those hardware events into mouse events for us.

Next I'd like to "map" the position of a square to one input - such as the mouse position - and the rotation of another to another input - such as the angle of my Wacom pen - and the color of another to whether or not the H-key on my keyboard is pressed, red if it is, blue otherwise.

I figure there are a total 4 different kinds of input that we as humans are able to provide the computer, irrespective of hardware, in either relative or absolute form, at various resolutions.

Types

• On/Off for any number of keys
• 1D Range
• 2D Range
• 3D Range

Examples

Event	Type	Mode	Resolution
Mouse 2D	2D Range	Rel	16-bit
Mouse 2D	2D Range	Abs	0-screen
Mouse Key	On/Off		3-10
Keyboard Key	On/Off		20-50
Keyboard WASD	2D Range	Rel	20-50
Wacom Position	2D Range	Abs	16-bit
Wacom Pressure	1D Range	Abs	0-4096
Wacom Angle	2D range	Abs	0-4096
Playstation Key	On/Off		4-12
Playstation D-Pad	2D Range	Abs	4-12
Playstation Range	1D Range	Abs	4-12
Playstation Touch	2D Range	Rel	256
iPad Touch	2D Range	Abs	256
iPad Gyro	2D Range	Abs	256
Index 3D	3D Range	Abs	16-bit
Index Key	On/Off		5-10
Index Finger	1D Range	Abs	256
GPS	2D Range	Abs	32-bit
Midi Key	On/Off		0-127
Midi Knob	1D Range	Rel	127
Midi Slider	1D Range	Abs	127
Midi 2D	2D Range	Abs	127
Midi 2D	2D Range	Rel	127
Midi Velocity	1D Range	Abs	0-127
Midi Aftertouch	1D Range		0-127
Motion Capture	3D Range		16-bit
Gesture	On/Off		1-n

I'd like to build my application around these 4 fundamental input types, and enable the user to pick any of these as sources from which to generate it.

Implementation

I'm not sure.

I figure there must at least be a translation layer. Something dedicated to interpreting the data coming from the device, like the mouse, Xbox or Valve Index controllers, the keyboard and so forth.

Your average application already provides two of these translation layers, for your mouse and for your keyboard.

void Application::mousePressEvent(...) {}
void Application::keyPressEvent(...) {}

That's great, we can translate these into our 4 general-purpose input handlers.

void Application::buttonEvent(...) {}
void Application::range1DEvent(...) {}
void Application::range2DEvent(...) {}
void Application::range3DEvent(...) {}

And now we can respond to these throughout our application, instead of to the mouse or keyboard directly. Then, when support for a new device is added, we can simply translate it to one or more of these 4 general purpose events.

To poll or not to poll

This one is always tricky. We don't care for events that happen more often than once every frame, and when we do care we want them to happen either at the beginning or end of each iteration.

For example, if an event comes in before the scene is rendered, then we can take it into account. If it comes in during a render, it's somewhat pointless. But that's exactly what could happen in the current example application, as drawing and receiving events are entirely separate and happen independently. (As far as I can tell?)

So polling seems the better option; at least in terms of predictability which I would trade for performance, if that is actually a tradeoff.

Unknowns

So input can come at any time, great. But some input have a distinct beginning and an end. Like dragging. Dragging is a combination of a button being pressed, a series of range2d's (in the case of a mouse) followed by a button being released.

Other input is a fire-and-forget type deal, like keyboard presses. Those are easier to conceptualise.