main.c File Reference

Two-layer parallax scrolling with player sprite. More...

#include <snes.h>
#include "res/BG1.inc"
#include "res/BG2.inc"
#include "res/character.inc"

Classes
struct	GameState
	Centralized game state structure. More...

Macros
Scroll Configuration
Constants controlling the auto-scroll behavior
#define	MAX_SCROLL_X   512
#define	SCROLL_THRESHOLD_LEFT   80
#define	SCROLL_THRESHOLD_RIGHT   140

Functions
int	main (void)
	Entry point – two-layer parallax scrolling with player sprite.

Variables
GameState	game = {20, 100, 0, 32, 0, 32}
	Global game state instance with initial values.

Detailed Description

Two-layer parallax scrolling with player sprite.

Demonstrates continuous horizontal scrolling with two independent background layers moving at different speeds (parallax) and a player-controlled sprite. BG1 and BG2 are loaded with separate tile sets and palettes in different VRAM/CGRAM slots to avoid conflicts. The scroll position is updated each frame based on player movement: when the sprite crosses a screen threshold, the background auto-scrolls and the player is pushed back, creating a camera-follow effect common in side-scrolling games. Scroll registers are written via bgSetScroll(), which defers the actual PPU register write to the NMI handler via a dirty-flag mechanism.

SNES Concepts

• Multi-layer parallax scrolling (BG1 + BG2 at independent speeds)
• Deferred scroll register writes via NMI dirty flags
• Multiple tile sets and palette slots in VRAM/CGRAM
• Sprite overlay on scrolling backgrounds
• Auto-scroll camera with player threshold tracking

What to Observe

• Move the character with D-pad; background scrolls when near screen edges
• BG1 and BG2 scroll together (parallax could use different speeds)
• The sprite animates and moves freely within the scroll boundaries

Modules Used

console, sprite, input, background, dma

See also

background.h, sprite.h, input.h, dma.h

Macro Definition Documentation

MAX_SCROLL_X

#define MAX_SCROLL_X   512

Maximum horizontal scroll (depends on tilemap size)

SCROLL_THRESHOLD_LEFT

#define SCROLL_THRESHOLD_LEFT   80

When player X < this, scroll left

SCROLL_THRESHOLD_RIGHT

#define SCROLL_THRESHOLD_RIGHT   140

When player X > this, scroll right

Function Documentation

main()

int main

(

void

)

Entry point – two-layer parallax scrolling with player sprite.

Loads two independent background layers (BG1 and BG2) with separate tile sets and palette slots, plus a character sprite. Each frame, the D-pad moves the player sprite; when the sprite crosses the scroll threshold, the backgrounds auto-scroll and the sprite is pushed back, creating a camera-follow effect. Scroll registers are deferred to the NMI handler via bgSetScroll()'s dirty-flag mechanism for safe VBlank-only writes.

Returns

Does not return (infinite loop).

< Current joypad button state (read from hardware)

< When player X > this, scroll right

< Maximum horizontal scroll (depends on tilemap size)

< When player X < this, scroll left

Variable Documentation

game

GameState game = {20, 100, 0, 32, 0, 32}

Global game state instance with initial values.