main.c File Reference

Game skeleton — the smallest complete game: title -> play -> over. More...

#include <snes.h>
#include <snes/input.h>

Macros
#define	PLAYER_SPEED   2
#define	PX_MAX   240
#define	PX_MIN   8
#define	PY_MAX   208
#define	PY_MIN   24
#define	SPR_VRAM   0x4000
#define	ST_OVER   2
#define	ST_PLAY   1
#define	ST_TITLE   0
	Game states — the whole game is a switch over these.
#define	START_TIME   30
#define	TILE_COIN   1
#define	TILE_PLAYER   0

Functions
static void	build_tile (const u8 *rows, u8 idx, u16 tile)
	Build an 8x8 tile from an 8-row bitmap, using palette index idx.
static void	draw_hud_labels (void)
	Print the fixed HUD labels once (numbers refreshed as they change).
static void	draw_score (void)
	Refresh the SCORE number (clear the field first so it never smears).
static void	draw_sprites (void)
	Draw the two gameplay sprites into the OAM buffer.
static void	draw_time (void)
	Refresh the TIME number.
static void	encode_4bpp (void)
	Pack pixbuf[] (8x8 palette indices) into a 4bpp planar tile.
int	main (void)
static void	show_over (void)
	Game-over screen.
static void	show_title (void)
	Title screen text.
static void	spawn_coin (void)
	Move the coin to a fresh pseudo-random spot.
static void	start_game (void)
	Enter the play state: reset score/timer, centre the player.
static void	update_play (u16 held)
	One frame of gameplay.

Variables
static u8	cx
static u8	cy
u8	game_state
	Probe oracle: current state (0 title, 1 play, 2 over).
static u8	pixbuf [64]
static u8	px
static u8	py
u16	score
	Probe oracle: coins collected.
static u16	seed_ctr
static u8	tick
static u8	tilebuf [32]
u8	time_left
	Probe oracle: seconds remaining in a round.

Detailed Description

Game skeleton — the smallest complete game: title -> play -> over.

The capstone the curriculum was missing: not a feature demo but the shape of a whole game, small enough to read in one sitting and fork for your own. It recombines the rungs you've climbed — input drives a sprite, a second sprite is a goal, a bounding-box test scores it, text is the HUD, and a hand-rolled state machine ties title, play and game-over together.

The one structural idea: a game is a state machine around one loop. Every frame you WaitForVBlank(), read the pad, then switch (game_state) to the code for the screen you're on. Transitions are just assignments to game_state plus a one-time setup for the new screen. That is the skeleton under every SNES game; basics/scene_stack shows the same idea lifted into the opt-in scene framework once the enum + switch starts to sprawl.

The game: steer the arrow with the D-pad, touch the coin to score, before the timer runs out. Zero assets — both sprites are built in C.

ROM mode: LoROM (project default).

Controls

• Title / Game over: START to begin / play again
• Play: D-pad to move; touch the coin to score

SNES Concepts

• The frame loop: WaitForVBlank -> read input -> update -> the NMI flushes
• A plain enum + switch state machine (title / play / over)
• Sprites (player + coin) via the OAM buffer; text HUD via the auto-flush
• Bounding-box collision; rand()/srand() seeded for varied coin spawns

What to Observe

Title shows "PRESS START". In play, moving onto the coin bumps SCORE and respawns it; TIME counts down; at zero the game-over screen shows the final score. game_state, score, time_left are the probe oracles.

Modules Used

console, dma, background, sprite, text, input

See also

examples/basics/scene_stack — the same idea via the scene framework

Macro Definition Documentation

PLAYER_SPEED

#define PLAYER_SPEED   2

PX_MAX

#define PX_MAX   240

PX_MIN

#define PX_MIN   8

PY_MAX

#define PY_MAX   208

PY_MIN

#define PY_MIN   24

SPR_VRAM

#define SPR_VRAM   0x4000

sprite tiles (text font is at $0000)

ST_OVER

#define ST_OVER   2

ST_PLAY

#define ST_PLAY   1

ST_TITLE

#define ST_TITLE   0

Game states — the whole game is a switch over these.

START_TIME

#define START_TIME   30

seconds on the clock

TILE_COIN

#define TILE_COIN   1

TILE_PLAYER

#define TILE_PLAYER   0

Function Documentation

build_tile()

void build_tile ( const u8 * rows, u8 idx, u16 tile )

static

Build an 8x8 tile from an 8-row bitmap, using palette index idx.

< sprite tiles (text font is at $0000)

draw_hud_labels()

void draw_hud_labels ( void )

static

Print the fixed HUD labels once (numbers refreshed as they change).

draw_score()

void draw_score ( void )

static

Refresh the SCORE number (clear the field first so it never smears).

draw_sprites()

void draw_sprites ( void )

static

Draw the two gameplay sprites into the OAM buffer.

draw_time()

void draw_time ( void )

static

Refresh the TIME number.

encode_4bpp()

void encode_4bpp ( void )

static

Pack pixbuf[] (8x8 palette indices) into a 4bpp planar tile.

main()

int main

(

void

)

< sprite tiles (text font is at $0000)

show_over()

void show_over ( void )

static

Game-over screen.

show_title()

void show_title ( void )

static

Title screen text.

spawn_coin()

void spawn_coin ( void )

static

Move the coin to a fresh pseudo-random spot.

start_game()

void start_game ( void )

static

Enter the play state: reset score/timer, centre the player.

< seconds on the clock

update_play()

void update_play ( u16 held )

static

One frame of gameplay.

Variable Documentation

cx

u8 cx

static

cy

u8 cy

static

game_state

u8 game_state

Probe oracle: current state (0 title, 1 play, 2 over).

pixbuf

u8 pixbuf[64]

static

px

u8 px

static

py

u8 py

static

score

u16 score

Probe oracle: coins collected.

seed_ctr

u16 seed_ctr

static

tick

u8 tick

static

tilebuf

u8 tilebuf[32]

static

time_left

u8 time_left

Probe oracle: seconds remaining in a round.