Basic Tutorials

Basic Game Tutorial #12 - Redefining controls

Introduction

This tutorial will demonstrate how to allow a user to redefine the controls for a game.

Compile and run tutorial18. You will be prompted to enter the controls to move the ship. Once you have entered them all you can move the ship around and fire using the controls you defined. Pressing Escape will allow you to redefine the controls again, pressing escape whilst on this screen will exit the program.

An in-depth look

The basic idea behind redefining controls is that you specify what key or joystick button has to be pressed to perform the onscreen action. This is accomplished by creating another Control structure to store your defined values. When you press a key or joystick button, this value is compared against the custom controls to see if one of them matches. If it does then the appropriate action will be performed.

The program comprises of two parts, defining the controls and then moving the ship with the defined controls. In defs.h we add a couple of defines to assist with the program flow

#define IN_REDEFINE 0
#define IN_GAME 1

typedef struct Game
{
	int score, status;
	SDL_Surface *screen;
	TTF_Font *font;
	SDL_Joystick *joystick;
} Game;

In structs.h we add another structure to assist with prompting the user to input their custom controls. It is very basic but serves its purpose for the tutorial.

typedef struct Redefine
{
	int redefineIndex;
	char redefineString[255];
} Redefine;

redefineIndex simply stores what key we're trying to redefine and redefineString is for the onscreen text. A fully fledged game would present the user with a menu and allow them to choose which control they want to redefine.

In main.c we initialize the redefineIndex 0 and blank the redefineString.

/* Reset the redefine index */

redefine.redefineIndex = 0;
redefine.redefineString[0] = '\0';

if (game.status == IN_REDEFINE)
{
	/* Handle the key redefining */

	doRedefine();
}

else
{
	/* Get the input */

	getInput();

	/* Update the player's position */

	doPlayer();

	/* Update the entities */

	doEntities();

	/* Do the collisions */

	doCollisions();

	/* Draw everything */

	draw();
}

In redefine.c, we check if the redefineString is blank. If it is then we will use the redefineIndex to determine which control we are currently prompting the user to define and generate the appropriate string. Next we call flushInputs, this function is in input.c and is defined as follows

void flushInputs()
{
	SDL_Event event;

	while (SDL_PollEvent(&event)) {}
}

int getSingleInput()
{
	int key;
	SDL_Event event;

	key = -2;

	if (SDL_PollEvent(&event))
	{
		switch (event.type)
		{
			case SDL_QUIT:
				exit(0);
			break;

			case SDL_KEYDOWN:
				key = event.key.keysym.sym;
			break;

			case SDL_JOYAXISMOTION:
				if (abs(event.jaxis.value) > DEAD_ZONE)
				{
					key = -3;
				}
			break;

			case SDL_JOYBUTTONDOWN:
				key = event.jbutton.button;
			break;
		}
	}

	if (key == SDLK_ESCAPE)
	{
		exit(0);
	}

	return key;
}

switch (redefine.redefineIndex)
{
	case 0:
		customControl.left = key;
		break;

	case 1:
		customControl.right = key;
		break;

	case 2:
		customControl.up = key;
		break;

	case 3:
		customControl.down = key;
		break;

	default:
		customControl.fire = key;
		break;
}

redefine.redefineIndex++;

redefine.redefineString[0] = '\0';

if (redefine.redefineIndex == 5)
{
	redefine.redefineIndex = 0;

	game.status = IN_GAME;
}

We will now look at how the custom controls are handled in input.c. The follow code snippet demonstrates this

case SDL_KEYDOWN:
	key = event.key.keysym.sym;

	if (key == customControl.left)
	{
		input.left = 1;
	}

	else if (key == customControl.right)
	{
		input.right = 1;
	}

	/* Remainder omitted */
	break;

case SDL_KEYUP:
	key = event.key.keysym.sym;

	if (key == customControl.left)
	{
		input.left = 0;
	}

	else if (key == customControl.right)
	{
		input.right = 0;
	}

	/* Remainder omitted */
	break;

case SDL_JOYBUTTONDOWN:
	key = event.jbutton.button;

	if (key == customControl.left)
	{
		input.left = 1;
	}

	else if (key == customControl.right)
	{
		input.right = 1;
	}

	/* Remainder omitted */
	break;

case SDL_JOYBUTTONUP:
	key = event.jbutton.button;

	if (key == customControl.left)
	{
		input.left = 0;
	}

  	else if (key == customControl.right)
	{
		input.right = 0;
	}

	/* Remainder omitted */
	break;

case SDL_JOYAXISMOTION:
	/* Horizontal movement */

	if (event.jaxis.axis == 0)
	{
		if (event.jaxis.value < -DEAD_ZONE)
		{
			input.left = 1;
		}

		else if (event.jaxis.value > DEAD_ZONE)
		{
			input.right = 1;
		}

		else
		{
			input.left = 0;
			input.right = 0;
		}
	}

	/* Vertical movement */

	if (event.jaxis.axis == 1)
	{
		if (event.jaxis.value < -DEAD_ZONE)
		{
			input.up = 1;
		}

		else if (event.jaxis.value > DEAD_ZONE)
		{
			input.down = 1;
		}

		else
		{
			input.up = 0;
			input.down = 0;
		}
	}
	break;

Conclusion

Probably the hardest thing about allowing a user to customize controls is building an elegant interface to allow them to do so. How major games companies are able to spend tens of millions of dollars on games and then overlook something so simple is a mystery.

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Source Code