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Two Players Example
Screenshot

Simultaneous multi-controller input handling.

Learning Objectives

After this lesson, you will understand:

  • Reading from multiple controller ports
  • Independent sprite control per player
  • Controller disconnection detection
  • Separate palettes for player identification

Prerequisites

  • Completed basic input examples
  • Understanding of sprite basics

What This Example Does

Two-player simultaneous control:

  • Player 1 (blue sprite) controlled by Controller 1
  • Player 2 (red sprite) controlled by Controller 2
  • Each player moves independently
  • Screen boundary checking for both
+----------------------------------------+
| |
| [P1 BLUE] [P2 RED] |
| |
| |
| |
| |
| Controller 1 Controller 2 |
+----------------------------------------+

Controls:

  • Controller 1 D-Pad: Move blue sprite (Player 1)
  • Controller 2 D-Pad: Move red sprite (Player 2)

Code Type

C with Direct Register Access

Component Type
Console init Library (consoleInit, setScreenOn)
Sprite display Library (oamInit, oamSet, oamUpdate)
Input reading Library (padHeld(0), padHeld(1))
Boundary check C code

Reading Two Controllers

Controller Registers

Register Address Purpose
JOY1L $4218 Controller 1 low byte
JOY1H $4219 Controller 1 high byte
JOY2L $421A Controller 2 low byte
JOY2H $421B Controller 2 high byte

Reading Both Controllers

/* Read both controllers (NMI handler reads joypads automatically) */
pad1 = padHeld(0);
pad2 = padHeld(1);
bx
static u16 bx
Definition main.c:159
padHeld
u16 padHeld(u8 pad)
Get buttons currently held.

Player State

Struct Pattern (Required)

Using a struct with s16 coordinates is required for reliable movement. Separate u16 variables cause horizontal movement issues due to a compiler quirk.

typedef struct {
s16 x, y;
} Player;
Player p1 = {64, 112};
Player p2 = {192, 112};
p2
u8 p2[]
Player 2 state, initialized at right-center of screen.
Definition main.c:103
p1
u8 p1[]
Player 1 state, initialized at left-center of screen.
Definition main.c:101
s16
signed short s16
16-bit signed integer (-32768 to 32767)
Definition types.h:49
Player
Per-player position state.
Definition main.c:95

Player Movement

Independent Control

/* Player 1 movement */
if (pad1 & KEY_RIGHT) { if (p1.x < 248) p1.x++; }
if (pad1 & KEY_LEFT) { if (p1.x > 0) p1.x--; }
if (pad1 & KEY_DOWN) { if (p1.y < 224) p1.y++; }
if (pad1 & KEY_UP) { if (p1.y > 0) p1.y--; }
/* Player 2 movement */
if (pad2 & KEY_RIGHT) { if (p2.x < 248) p2.x++; }
if (pad2 & KEY_LEFT) { if (p2.x > 0) p2.x--; }
if (pad2 & KEY_DOWN) { if (p2.y < 224) p2.y++; }
if (pad2 & KEY_UP) { if (p2.y > 0) p2.y--; }
KEY_RIGHT
#define KEY_RIGHT
Definition input.h:78
KEY_DOWN
#define KEY_DOWN
Definition input.h:76
KEY_LEFT
#define KEY_LEFT
Definition input.h:77
KEY_UP
#define KEY_UP
Definition input.h:75

Player Differentiation

Separate Palettes

/* Palette 0: Blue (Player 1) */
REG_CGADD = 128;
REG_CGDATA = 0xE0; REG_CGDATA = 0x7C; /* Blue */
/* Palette 1: Red (Player 2) */
REG_CGADD = 128 + 16;
REG_CGDATA = 0x1F; REG_CGDATA = 0x00; /* Red */
REG_CGADD
#define REG_CGADD
CGRAM address (W)
Definition registers.h:148
REG_CGDATA
#define REG_CGDATA
CGRAM data write (W)
Definition registers.h:151

Sprite Setup

/* Player 1: Palette 0 (blue) */
oamSet(0, p1.x, p1.y, 0, 0, 3, 0);
/* Player 2: Palette 1 (red) */
oamSet(1, p2.x, p2.y, 0, 1, 3, 0);
oamSet
void oamSet(u16 id, u16 x, u16 y, u16 tile, u16 palette, u16 priority, u16 flags)
Set sprite properties.

Controller Detection

Disconnected Controller

/* 0xFFFF indicates no controller connected */
if (pad2 == 0xFFFF) {
/* Controller 2 not connected */
/* Could display "CONNECT CONTROLLER 2" */
}

Controller Types

The SNES supports various controllers:

  • Standard gamepad (most common)
  • Mouse
  • Super Scope
  • Multitap (4+ players)

Build & Run

cd $OPENSNES_HOME
make -C examples/input/two_players

Then open two_players.sfc in your emulator (Mesen2 recommended). Configure the emulator for two controllers.

Files

File Purpose
main.c Two-player input handling, sprite setup, palette
Makefile Build configuration (LIB_MODULES := console input sprite dma text)

Exercises

Exercise 1: Player Collision

Detect when players touch:

if (abs(p1.x - p2.x) < 16 && abs(p1.y - p2.y) < 16) {
/* Players colliding! */
}

Exercise 2: Different Speeds

Give players different speeds:

#define P1_SPEED 2
#define P2_SPEED 3 /* Faster */

Exercise 3: Button Actions

Add button-triggered actions:

if (pad1 & KEY_A) {
/* Player 1 action */
}
if (pad2 & KEY_A) {
/* Player 2 action */
}
KEY_A
#define KEY_A
Definition input.h:81

Exercise 4: Split Screen

Implement split-screen view for versus games (advanced):

/* Use windows to divide screen */
/* Each player has their own camera */

Technical Notes

Auto-Joypad Read

The SNES automatically reads controllers during VBlank:

  • Enabled by NMITIMEN register
  • Takes ~4 scanlines
  • Check HVBJOY bit 0 for completion

Multitap Support

For more than 2 players, use the multitap:

  • Requires different register access
  • Up to 4-5 players depending on adapter

Input Latency

Controller reads happen once per frame:

  • 60Hz = ~16.7ms input latency
  • Additional latency from game logic

Button Layout

Both controllers have identical mapping:

Bit 15: B Bit 7: A
Bit 14: Y Bit 6: X
Bit 13: Select Bit 5: L
Bit 12: Start Bit 4: R
Bit 11: Up Bits 3-0: ID (always $F)
Bit 10: Down
Bit 9: Left
Bit 8: Right

What's Next?

Collision: Collision Demo - Hit detection

Game: Breakout - Complete game with collision and sprites