Animated Sprite -- Direction States and Sprite Sheets

Screenshot

What This Example Shows

How to animate a character sprite that walks in 4 directions with 3 animation frames each. Demonstrates sprite sheet layout, direction state machines, and horizontal flip to reuse art.

Prerequisites

Read sprites/simple_sprite first (OAM basics, tile loading).

Controls

Button	Action
D-PAD Up	Walk up
D-PAD Down	Walk down
D-PAD Left	Walk left (flipped)
D-PAD Right	Walk right

Build & Run

cd $OPENSNES_HOME
make -C examples/graphics/sprites/animated_sprite

Then open animated_sprite.sfc in your emulator (Mesen2 recommended).

How It Works

1. Sprite sheet layout

The sprite sheet is a PNG strip containing 9 frames of 16x16 sprites, loaded to VRAM at startup via oamInitGfxSet(). Each 16x16 sprite occupies 2 tile columns in VRAM. The frame index maps to tile numbers:

• Walking down: tiles 0, 2, 4
• Walking up: tiles 6, 8, 10
• Walking right: tiles 12, 14, 32
• Walking left: same as right, but with OBJ_FLIPX

2. State machine

enum SpriteState {
    W_DOWN = 0,
    W_UP = 1,
    W_RIGHT = 2,
    W_LEFT = 2  /* Reuses W_RIGHT with flipx */
};

Left and right share the same animation row – the PPU's horizontal flip flag (OBJ_FLIPX) mirrors the sprite at zero CPU cost. This is a standard SNES technique that halves the sprite art needed for left/right movement.

3. Animation timing

monster.anim_delay++;
if (monster.anim_delay >= ANIM_DELAY) {
    monster.anim_delay = 0;
    monster.anim_frame++;
    if (monster.anim_frame >= 3) monster.anim_frame = 0;
}

Animation only advances when a direction button is held. ANIM_DELAY (6 frames) controls walking speed – at 60 fps, this means about 10 animation steps per second.

4. Tile calculation

The tile number is computed from the state and frame:

if (state == W_DOWN)  tile = frame * 2;          /* 0, 2, 4 */
if (state == W_UP)    tile = 6 + frame * 2;      /* 6, 8, 10 */
if (state == W_RIGHT) tile = 12 + frame * 2;     /* 12, 14, (32) */

Frame 2 of the right-walk is at tile 32 (next row in VRAM) because the sheet wraps at 16 tiles per row.

SNES Concepts

OBJ_FLIPX – Hardware Horizontal Mirror

The PPU can flip any sprite horizontally by setting a single bit in the OAM attribute byte. This costs nothing – no extra tiles in VRAM, no CPU work. Many SNES games use this to halve the sprite art needed for left/right movement.

Sprite Sheets in VRAM

All animation frames are loaded into VRAM at once via oamInitGfxSet(). The active frame is selected by changing the tile number in oamSet(). This means switching frames is instant – just change a number, no DMA needed.

16x16 Tiles in OAM

In OAM, a 16x16 sprite uses 4 hardware 8x8 tiles arranged in a 2x2 grid. The tile number refers to the top-left tile; the PPU fills in the rest automatically using the SNES tile numbering convention (right tile = tile+1, bottom tiles follow the 16-tile-per-row VRAM layout).

Project Structure

File	Purpose
main.c	Input handling, state machine, animation logic
data.asm	Sprite tile data and palette via .INCBIN
res/sprites.png	Source sprite sheet (9 frames, 16x16 each)
Makefile	LIB_MODULES := console sprite dma input

Going Further

• Add diagonal movement: Check for simultaneous Up+Right, Down+Left, etc. Choose a direction state based on the last-pressed direction.
• Variable walk speed: Use fixed-point positions (8.8 format) for sub-pixel movement. This gives smoother motion at speeds between 1 and 2 pixels per frame.
• Explore related examples:
  • sprites/dynamic_sprite – Stream frames instead of pre-loading all of them
  • games/breakout – Multiple sprites interacting with game logic