main.c File Reference

Colour, rung 6c.2 — shadow & tint: recolour a whole scene at once. More...

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

Functions
static void	apply_effect (void)
	Apply the effect for the current fx_state (call after VBlank).
static void	build_scene_palette (void)
	Fill scene_pal[] with a believable slice of a game world.
static void	build_solid_tile (u8 v)
	Fill tilebuf with a solid 4bpp tile of palette index v.
int	main (void)

Variables
u8	fx_state
	Probe oracle: current effect (0 none, 1 shadow, 2 underwater, 3 sunset).
static u16	rowbuf [32]
	One tilemap row (32 entries).
static u16	scene_pal [16]
	16 game-world colours, filled at init (RAM — no ROM const)
static u8	tilebuf [32]
	One solid 4bpp tile (two interleaved bitplane pairs, 32 bytes).

Detailed Description

Colour, rung 6c.2 — shadow & tint: recolour a whole scene at once.

Colour math against a fixed colour is how a game changes mood without touching a single tile or palette entry. Subtract a grey and the scene darkens — dusk, a dungeon, nightfall. Add a colour and the scene takes that cast — the blue of being underwater, the orange of a sunset or lava glow, the red flash of taking a hit. One register pair does it to every pixel of a layer, every frame, for free.

The scene here is a 4x4 chart of sixteen game-world colours (sky, water, foliage, earth, stone, accents) built procedurally — zero assets — so you can watch the effect land on every hue at once. Press A to cycle:

none -> shadow (darken) -> underwater tint -> sunset tint -> none

ROM mode: LoROM (project default).

SNES Concepts

• Colour math with the FIXED-colour source (COLDATA $2132): result is main-screen ± a constant, applied per enabled layer
• colorMathShadow() = subtract grey (darken); colorMathTint() = add a colour (cast) — the two share the fixed-colour register and the add/subtract bit, so only one is active at a time
• The effect is a PPU pass over the final image: no VRAM, CGRAM or OAM traffic, so it costs nothing per frame and scales to the whole screen

What to Observe

Boot: the plain colour chart. Press A to darken it (shadow), then wash it blue (underwater), then warm it (sunset), then back to plain. Every swatch shifts together. fx_state is the probe oracle (0..3).

Modules Used

console, dma, background, colormath, input

See also

lib/include/snes/colormath.h — colorMathShadow(), colorMathTint()

Function Documentation

apply_effect()

void apply_effect ( void )

static

Apply the effect for the current fx_state (call after VBlank).

build_scene_palette()

void build_scene_palette ( void )

static

Fill scene_pal[] with a believable slice of a game world.

Four rows of four: sky/water, foliage, earth/stone, accents. Vivid enough that both a darken and a colour cast read clearly on every one.

build_solid_tile()

void build_solid_tile ( u8 v )

static

Fill tilebuf with a solid 4bpp tile of palette index v.

4bpp planar: rows 0-7 store bitplane pair (0,1) as 16 bytes, then pair (2,3). Each plane byte is $FF or $00 per the matching bit of v.

main()

int main

(

void

)

Variable Documentation

fx_state

u8 fx_state

Probe oracle: current effect (0 none, 1 shadow, 2 underwater, 3 sunset).

rowbuf

u16 rowbuf[32]

static

One tilemap row (32 entries).

scene_pal

u16 scene_pal[16]

static

16 game-world colours, filled at init (RAM — no ROM const)

tilebuf

u8 tilebuf[32]

static

One solid 4bpp tile (two interleaved bitplane pairs, 32 bytes).