Games at Bolton Joysticks Andrew Williams A.Williams@bolton.ac.uk.

Joysticks

Andrew Williams

http://www.bolton.ac.uk/staff/adw1

A.Williams@bolton.ac.uk

Reference

Joystick handling is covered in great detail here:– http://sdldoc.csn.ul.ie/

guideinput.php#AEN163

Digital vs Analogue Digital

– On or off– Buttons– The “Hat” (SDL)

Analog(ue)– Joysticks– A range of values

• (-32768 to +32767) for SDL

A PS2-Style Joypad

Modern gamepadshave both analogue

and digital

A PS2-Style Joypad“Hat”

A PS2-Style Joypad

8-wayDirectional

Control

“Hat”

A PS2-Style Joypad

SDL treatsit as digital

“Hat”

A PS2-Style JoypadJoysticks

A PS2-Style Joypad

SDL treatsthese asanalogue

Joysticks

A PS2-Style JoypadButtons

A PS2-Style JoypadButtons

SDL treatsthese asdigital

A PS2-Style JoypadButtons

Don't forgetthe shoulder

buttons

Joysticks and SDL

Reference:– Joystick handling in SDL is covered in

great detail here in the SDL documentation (see the GHAP webpage)

Initializing SDL This assumes only one joystick

– SDL has functionality for discovering how many joysticks there are and what type they are, etc

/* initialize SDL */SDL_Init(SDL_INIT_VIDEO | SDL_INIT_JOYSTICK| SDL_INIT_TIMER);

/* Open the Joystick */SDL_Joystick *joystick;SDL_JoystickEventState(SDL_ENABLE);joystick = SDL_JoystickOpen(0);

Joystick Event-Handling while(SDL_PollEvent(&event)) { switch(event.type) { case SDL_KEYDOWN: /* handle keyboard stuff here */ break;

case SDL_JOYAXISMOTION: /* handle joystick motion here * (see next slide) */ break; } }

/* handle joystick motion here */

case SDL_JOYAXISMOTION: /* handle joystick motion here */if(SDL_JoystickGetAxis(joystick, 0) < -3200) {

xMove = -2;} else if(SDL_JoystickGetAxis(joystick, 0) > +3200) {

xMove = +2;} else {

xMove = 0;}if(SDL_JoystickGetAxis(joystick, 1) < -3200) {

yMove = -2;} else if(SDL_JoystickGetAxis(joystick, 1) > +3200) {

yMove = +2;} else {

yMove = 0;}

break;

Analogue The example on the previous slide

simply treats the joystick as a digital device: it is moved either to the left or the right

This is not really appropriate for an analogue device– To use it properly, we should reflect how

far the joystick has been moved• The further it has been moved, the faster the

movement

Analogue Joystick Motioncase SDL_JOYAXISMOTION:

/* handle joystick motion here */if(SDL_JoystickGetAxis(joystick, 0) < -22000) {

xMove = -8;} else if(SDL_JoystickGetAxis(joystick, 0) < -12200) {

xMove = -4;} else if(SDL_JoystickGetAxis(joystick, 0) < -3200) {

xMove = -2;} else if(SDL_JoystickGetAxis(joystick, 0) > +22000) {

xMove = +8;} else if(SDL_JoystickGetAxis(joystick, 0) > +12200) {

xMove = +4;} else if(SDL_JoystickGetAxis(joystick, 0) > +3200) {

xMove = +2;} else {

xMove = 0;}/* You'd need something similar for the y dimension */break;

Joystick Buttonscase SDL_JOYBUTTONDOWN: /* Joystick Button Press */

if( event.jbutton.button == 0 ) { firingMachineGun = true;

}if(event.jbutton.button == 1) {

firingRockets = true;}break;

case SDL_JOYBUTTONUP: /* Joystick Button Release */if( event.jbutton.button == 0 ) {

firingMachineGun = false;}if(event.jbutton.button == 1) {

firingRockets = false;}break;

Continued overleaf

Joystick Buttons (continued) You fire machine guns and/or rockets after the switch statement:

switch(event.type) {/* blah blah

* see previous slides * blah blah */

}

if(firingMachineGuns) {/* handle machine gun firing */

}if(firingRockets) {

/* handle rocket firing */}