main.c File Reference

Direct color — the pixel byte IS the color (CGWSEL bit 0). More...

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

Functions
static void	build_solid_tile (u8 v)
	Fill tilebuf with a solid 8bpp tile of pixel value v.
int	main (void)

Variables
u8	direct_on
	Probe oracle: 1 while direct color is active.
static u16	graybuf [256]
	Grayscale CGRAM ramp (256 x 15-bit).
static u16	rowbuf [32]
	One tilemap row (32 entries).
static u8	tilebuf [64]
	One 8bpp tile (4 interleaved bitplane pairs, 64 bytes).

Detailed Description

Direct color — the pixel byte IS the color (CGWSEL bit 0).

Effects arc 4/7 (#109). In direct color mode the PPU stops looking 8bpp BG pixels up in CGRAM: each pixel byte is read as BBGGGRRR and expanded straight to 15-bit BGR. This example builds a 16x16 chart of all 256 pixel codes procedurally (zero assets, 256 solid-color tiles generated at init) and loads a deliberately DIFFERENT CGRAM palette — a grayscale ramp — so one button press flips the SAME VRAM bytes between two readings:

• direct ON (boot state): the BBGGGRRR color cube — red ramps left-to-right within each block row, green down the chart, blue in four broad bands;
• direct OFF: the CGRAM grayscale ramp of the very same tile data.

ROM mode: LoROM (project default).

SNES Concepts

• CGWSEL bit 0 via colorMathSetDirectColor() — the colormath module shadows the register, so this composes with any blending setup
• BBGGGRRR expansion and the tilemap-palette-bits low-bit extension (2048 colors max — this chart uses pal bits 0, the base 256)
• Mode 3: BG1 is 8bpp; 8bpp tile format = 4 interleaved bitplane pairs (64 bytes/tile), built here byte by byte in C

What to Observe

Boot shows the color cube. Press A to re-read the same VRAM as grayscale (CGRAM mode), press again to return. Nothing is uploaded on toggle — one register bit changes the meaning of every pixel.

Modules Used

console, dma, background, colormath, input

See also

lib/include/snes/colormath.h — colorMathSetDirectColor()

Function Documentation

build_solid_tile()

void build_solid_tile ( u8 v )

static

Fill tilebuf with a solid 8bpp tile of pixel value v.

8bpp planar layout: rows store plane pairs 0-1, then 2-3, 4-5, 6-7 in 16-byte groups. A solid tile makes every row byte of plane p either $FF or $00 depending on bit p of v.

main()

int main

(

void

)

Variable Documentation

direct_on

u8 direct_on

Probe oracle: 1 while direct color is active.

graybuf

u16 graybuf[256]

static

Grayscale CGRAM ramp (256 x 15-bit).

rowbuf

u16 rowbuf[32]

static

One tilemap row (32 entries).

tilebuf

u8 tilebuf[64]

static

One 8bpp tile (4 interleaved bitplane pairs, 64 bytes).