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SNES Graphics Programming Guide

This guide covers everything needed to create graphics for SNES games using OpenSNES.

Table of Contents

  1. PPU Architecture
  2. Video Modes
  3. Backgrounds
  4. Sprites
  5. Metasprites
  6. VRAM Layout
  7. Palettes
  8. Asset Requirements
  9. Tools & Resources

PPU Architecture

The SNES uses two PPU chips working together:

Chip Name Function
PPU1 5C77 "The Brain" - addresses VRAM, makes rendering decisions
PPU2 5C78 "The Compositor" - generates video signal, accesses palettes

Memory Systems

Memory Size Purpose
VRAM 64 KB Tiles, tilemaps for backgrounds and sprites
OAM 544 bytes Sprite attributes (128 sprites)
CGRAM 512 bytes Color palettes (256 colors × 15-bit)

Video Modes

The SNES supports 8 background modes. Mode 1 is most common for games:

Mode BG1 BG2 BG3 BG4 Notes
0 2bpp 2bpp 2bpp 2bpp 4 layers, 4 colors each
1 4bpp 4bpp 2bpp - Most common - 2×16 colors + 1×4 colors
2 4bpp 4bpp - - Per-tile offset (parallax)
3 8bpp 4bpp - - 256 colors + 16 colors
4 8bpp 2bpp - - Per-tile offset
5 4bpp 2bpp - - Hi-res (512px wide)
6 4bpp - - - Hi-res + per-tile offset
7 8bpp - - - Rotation/scaling (Mode 7)

Mode 1 Setup (Recommended)

REG_BGMODE = 0x01; // Mode 1, 8x8 tiles
// BG1: 16 colors (4bpp) - main playfield
// BG2: 16 colors (4bpp) - parallax/details
// BG3: 4 colors (2bpp) - HUD/status bar
REG_BGMODE
#define REG_BGMODE
BG mode and tile size (W)
Definition registers.h:64

Backgrounds

Tilemap Structure

Each tilemap entry is 16 bits:

VHOP PPCC CCCC CCCC
│││ ││└─────────── Tile number (0-1023)
│││ └└───────────── Palette (0-7)
││└───────────────── Priority (0-1)
│└────────────────── Horizontal flip
└─────────────────── Vertical flip

Tilemap Sizes

Setting Tiles Pixels Memory
32×32 1024 256×256 2 KB
64×32 2048 512×256 4 KB
32×64 2048 256×512 4 KB
64×64 4096 512×512 8 KB

Tile Formats

Bit Depth Colors Bytes/Tile Use Case
2bpp 4 16 bytes HUD, simple BG
4bpp 16 32 bytes Main backgrounds
8bpp 256 64 bytes Detailed art

Sprites

OAM Structure (544 bytes total)

Main Table (512 bytes, 4 bytes × 128 sprites):

Byte Bits Content
0 7-0 X position (low 8 bits)
1 7-0 Y position
2 7-0 Tile number (low 8 bits)
3 7 Vertical flip
3 6 Horizontal flip
3 5-4 Priority (0-3)
3 3-1 Palette (0-7, from CGRAM $80-$FF)
3 0 Tile number bit 8

Extended Table (32 bytes, 2 bits × 128 sprites):

  • Bit 0: X position bit 8 (for X > 255)
  • Bit 1: Size select (0=small, 1=large)

Sprite Sizes

Register $2101 selects two sizes (small/large):

OBJSEL Small Large
0 8×8 16×16
1 8×8 32×32
2 8×8 64×64
3 16×16 32×32
4 16×16 64×64
5 32×32 64×64
6 16×32 32×64
7 16×32 32×32

Scanline Limits (Critical!)

Limit Value Consequence
Sprites/line 32 max Higher OAM index sprites dropped
Slivers/line 34 max Sprite parts clipped

Solution: Rotate OAM priority each frame to distribute flicker.

Sprite Priority

Within OBJ layer: Lower OAM index = on top With backgrounds: Priority bits 0-3 interleave with BG layers

Metasprites

Metasprites combine multiple hardware sprites into one logical entity.

Data Format Example

// Each entry: X offset, Y offset, tile, attributes
const u8 player_idle[] = {
// Sprite 0: top-left
0, 0, 0x00, 0x30,
// Sprite 1: top-right
8, 0, 0x01, 0x30,
// Sprite 2: bottom-left
0, 8, 0x10, 0x30,
// Sprite 3: bottom-right
8, 8, 0x11, 0x30,
0xFF // End marker
};
bx
static u16 bx
Definition main.c:159
u8
unsigned char u8
8-bit unsigned integer (0 to 255)
Definition types.h:46

Animation State Machine

typedef struct {
u8 frame; // Current frame index
u8 timer; // Frame duration counter
u8 loop_start; // Frame to loop back to
const u8** frames; // Array of metasprite pointers
} Animation;
void animation_update(Animation* anim) {
if (--anim->timer == 0) {
anim->frame++;
if (anim->frames[anim->frame] == NULL) {
anim->frame = anim->loop_start;
}
anim->timer = FRAME_DURATION;
}
}
NULL
#define NULL
Null pointer constant.
Definition types.h:142
frame
u16 frame
Current sprite tile number.
Definition main.c:81

VRAM Layout

Recommended Layout (Mode 1)

Address Size Content
$0000 24 KB BG tiles (4bpp, 768 tiles)
$6000 2 KB BG1 tilemap
$6800 2 KB BG2 tilemap
$7000 2 KB BG3 tilemap
$8000 16 KB Sprite tiles (4bpp, 512 tiles)

VRAM Address Registers

Register Purpose
$2107 BG1 tilemap address (bits 7-2 × $400)
$2108 BG2 tilemap address
$2109 BG3 tilemap address
$210B BG1/2 tile address (nibbles × $1000)
$210C BG3/4 tile address
$2101 Sprite tile address + size select

Palettes

CGRAM Layout (256 colors × 2 bytes)

Range Colors Use
$00-$7F 128 Background palettes (8 × 16 colors)
$80-$FF 128 Sprite palettes (8 × 16 colors)

Color Format (15-bit BGR)

0BBB BBGG GGGR RRRR
│││││││││││└────── Red (0-31)
│││││└└└└└──────── Green (0-31)
└└└└└───────────── Blue (0-31)

Palette Selection

Backgrounds: Tilemap bits 10-12 select palette 0-7 Sprites: OAM byte 3 bits 1-3 select palette 0-7 (from upper CGRAM)

Asset Requirements

For SNES Compatibility

Asset Type Requirements
Tiles 8×8 pixels, indexed color
BG Palette Max 16 colors per palette (4bpp)
Sprite Palette Max 16 colors, color 0 = transparent
Tilemap Max 1024 unique tiles per layer
Character 16×16 to 32×32 typical

Recommended Workflow

  1. Create art in any tool (Aseprite, GIMP, Photoshop)
  2. Reduce colors to 16 per palette
  3. Export as indexed PNG (8×8 grid alignment)
  4. Convert with gfx4snes or similar tool
  5. Load via DMA during VBlank

Tools & Resources

Graphics Conversion Tools

Tool Purpose Link
gfx4snes PNG to SNES tiles/palettes OpenSNES/tools
M1TE2 Tile editor, map maker Third-party
SuperTileMapper VRAM/tilemap editor GitHub
Aseprite Pixel art (paid) aseprite.org
GIMP Free image editor gimp.org

Free Asset Sources (CC0/Public Domain)

Source Link
itch.io CC0 Pixel Art https://itch.io/game-assets/assets-cc0/tag-pixel-art
itch.io 16-bit Assets https://itch.io/game-assets/free/tag-16-bit
OpenGameArt CC0 https://opengameart.org/content/cc0-resources
Kenney Assets https://kenney.nl/assets (CC0)

Documentation

Resource Description
SNESdev Wiki - Sprites Comprehensive sprite reference
Super Famicom Wiki Hardware documentation
nesdoug tutorials C/ASM tutorials with examples
Fabien Sanglard PPU Deep PPU internals

Quick Reference

Register Cheat Sheet

$2100 INIDISP - Screen on/off, brightness
$2101 OBJSEL - Sprite VRAM address, sizes
$2105 BGMODE - Background mode, tile size
$2107 BG1SC - BG1 tilemap address, size
$210B BG12NBA - BG1/2 tile address
$212C TM - Main screen layer enable
$212D TS - Sub screen layer enable
$2115 VMAIN - VRAM address increment mode
$2116 VMADDL - VRAM address (low)
$2117 VMADDH - VRAM address (high)
$2118 VMDATAL - VRAM data write (low)
$2119 VMDATAH - VRAM data write (high)
$2121 CGADD - Palette address
$2122 CGDATA - Palette data write

DMA Registers (for fast transfers)

$4300 DMAP0 - DMA parameters
$4301 BBAD0 - B-bus address ($18 for VRAM, $22 for CGRAM)
$4302 A1T0L - Source address (low)
$4303 A1T0H - Source address (high)
$4304 A1B0 - Source bank
$4305 DAS0L - Transfer size (low)
$4306 DAS0H - Transfer size (high)
$420B MDMAEN - Start DMA (bit 0 = channel 0)