main.c File Reference

HiColor — 1792 colors on screen from a 4bpp background. More...

#include <snes.h>
#include "res/sunset.inc"

Macros
#define	VRAM_GFX   0x0000
	BG2 tiles at VRAM word $0000 (28672 bytes).
#define	VRAM_MAP_BASE   0x3C00
	BG2 32x32 map base (word address).
#define	VRAM_MAP_LOAD   0x3C80
	Map loads at row 4: scroll y = 32 makes screen line 0 show map row 4 (the lib writes VOFS = y - 1 itself; krom's raw 31 is the same intent).

Functions
static void	buildTilemap (void)
	Build krom's tilemap pattern: sequential tiles; even rows use palettes 0-3, odd rows 4-7 (the CGRAM ping-pong); one sub-palette per 64-pixel screen quarter (matches the converter's 64x8 segments).
void	hicolorIrqStream (void)
	Per-scanline CGRAM streaming IRQ handler (irq_stream.asm).
static void	hicolorVblank (void)
	VBlank: rewind the palette stream for the new frame.
int	main (void)

Variables
static u16	pal_offset
	16-bit offset of sunset_pal within its bank (IRQ stream source)
static u16	tilemap [896]
	Generated 32x28 tilemap (krom's fixed pattern — see buildTilemap).

Detailed Description

HiColor — 1792 colors on screen from a 4bpp background.

Port of krom (Peter Lemon)'s HiColor64PerTileRow demo (SNES/PPU/HDMA/HiColor64PerTileRow), the canonical "beat the palette ceiling" technique. An H-timer IRQ fires on EVERY scanline and DMAs 16 bytes (8 colors) into CGRAM while the PPU is drawing; over one 8-line tile row that streams a full fresh 64-color set. Even tile rows render from CGRAM colors 0-63 while the stream refills 64-127 for the odd row, and vice versa — 28 rows x 64 = 1792 colors from a background mode that nominally allows 128.

SNES Concepts

• H-timer IRQ ($4207/$4200 bit 4) — per-scanline CPU interrupts
• Raw IRQ handlers via irqSet() (see irq_stream.asm — ASM only)
• General DMA to CGRAM ($2122) during active display
• CGRAM double-banking via tilemap palette bits (rows alternate 0-3 / 4-7)
• The NMITIMEN shadow: nmiSet/irqEnable compose instead of clobbering

What to Observe

A sunset over water with perfectly smooth gradients — 377 distinct colors on screen (measure any static 4bpp screen: max 128). The top of each 8-pixel band is where the palette race lives; the H-timer is set so the DMA lands in H-blank for THIS handler (128, not krom's 190 — see the comment at irqSetHTimer()).

Modules Used

console, dma, background

See also

https://github.com/PeterLemon/SNES — original demo & converter

docs/tutorials/graphics.md

Macro Definition Documentation

VRAM_GFX

#define VRAM_GFX   0x0000

BG2 tiles at VRAM word $0000 (28672 bytes).

VRAM_MAP_BASE

#define VRAM_MAP_BASE   0x3C00

BG2 32x32 map base (word address).

VRAM_MAP_LOAD

#define VRAM_MAP_LOAD   0x3C80

Map loads at row 4: scroll y = 32 makes screen line 0 show map row 4 (the lib writes VOFS = y - 1 itself; krom's raw 31 is the same intent).

Function Documentation

buildTilemap()

void buildTilemap ( void )

static

Build krom's tilemap pattern: sequential tiles; even rows use palettes 0-3, odd rows 4-7 (the CGRAM ping-pong); one sub-palette per 64-pixel screen quarter (matches the converter's 64x8 segments).

hicolorIrqStream()

void hicolorIrqStream ( void )

extern

Per-scanline CGRAM streaming IRQ handler (irq_stream.asm).

hicolorVblank()

void hicolorVblank ( void )

static

VBlank: rewind the palette stream for the new frame.

Reloads CGRAM 0-63 with row 0's colors (128 bytes) and resets the DMA source to the table start. The per-scanline IRQ then streams the remaining 27 rows during active display, the source address auto-advancing across transfers. Mirrors krom's VBLANKIRQ verbatim.

main()

int main

(

void

)

Variable Documentation

pal_offset

u16 pal_offset

static

16-bit offset of sunset_pal within its bank (IRQ stream source)

tilemap

u16 tilemap[896]

static

Generated 32x28 tilemap (krom's fixed pattern — see buildTilemap).