c8.html

<canvas id=C width=64></canvas><a href=//github.com/xem/chip8><img style="position:absolute;top:0;right:0;border:0;" src="https://s3.amazonaws.com/github/ribbons/forkme_right_darkblue_121621.png" alt="Fork me on GitHub"></a><h1>1kb chip8 emulator</h1><h2>Commented cource code, with sound</h2><div><a href=.>Homepage</a><br><br>Choose a ROM:<br><a href="c8.html?1#ROM/C8PIC.ch8">C8PIC</a><br><a href="c8.html?2#ROM/IBM.ch8">IBM</a><br><a href="c8.html?3#ROM/Rocket2.ch8">Rocket2</a> (press Y to launch)<br><a href="c8.html?4#ROM/X-MIRROR.ch8">X-MIRROR</a> (press 2,4,6,8 to draw)<br><a href="c8.html?5#ROM/TAPEWORM.ch8">TAPEWORM</a> (Y to start, 2,4,6,8 to move)<br><a href="c8.html?6#ROM/TIMEBOMB.ch8">TIMEBOMB</a> (set up with 2 and 8, start with 5)<br><a href="c8.html?8#ROM/AIRPLANE.ch8">AIRPLANE</a> (send bombs with 2)<br><a href="c8.html?10#ROM/BLITZ.ch8">BLITZ</a> (send bombs with 2)<br><a href="c8.html?11#ROM/BREAKOUT.ch8">BREAKOUT</a> (move with 4 and 6)<br><a href="c8.html?12#ROM/BRIX.ch8">BRIX</a> (move with 4 and 6)<br><a href="c8.html?13#ROM/CAVE.ch8">CAVE</a> (start with Y, move with 2,4,6,8)<br><a href="c8.html?14#ROM/CONNECT4.ch8">CONNECT4</a><br><a href="c8.html?15#ROM/FIGURES.ch8">FIGURES</a><br><a href="c8.html?16#ROM/FILTER.ch8">FILTER</a><br><a href="c8.html?17#ROM/GUESS.ch8">GUESS</a><br><a href="c8.html?18#ROM/HIDDEN.ch8">HIDDEN</a><br><a href="c8.html?19#ROM/INVADERS.ch8">INVADERS</a><br><a href="c8.html?20#ROM/KALEID.ch8">KALEID</a><br><a href="c8.html?21#ROM/LANDING.ch8">LANDING</a><br><a href="c8.html?22#ROM/MAZE.ch8">MAZE</a><br><a href="c8.html?23#ROM/MERLIN.ch8">MERLIN</a><br><a href="c8.html?24#ROM/MISSILE.ch8">MISSILE</a><br><a href="c8.html?25#ROM/PADDLES.ch8">PADDLES</a><br><a href="c8.html?26#ROM/PONG (1P).ch8">PONG (1P)</a><br><a href="c8.html?27#ROM/PONG.ch8">PONG</a><br><a href="c8.html?28#ROM/PONG2.ch8">PONG2</a><br><a href="c8.html?29#ROM/PUZZLE.ch8">PUZZLE</a><br><a href="c8.html?30#ROM/ROCKET.ch8">ROCKET</a><br><a href="c8.html?31#ROM/SOCCER.ch8">SOCCER</a><br><a href="c8.html?32#ROM/SPACEF.ch8">SPACEF</a><br><a href="c8.html?33#ROM/SQUASH.ch8">SQUASH</a><br><a href="c8.html?34#ROM/SYZYGY.ch8">SYZYGY</a><br><a href="c8.html?35#ROM/TANK.ch8">TANK</a><br><a href="c8.html?36#ROM/TETRIS.ch8">TETRIS</a><br><a href="c8.html?37#ROM/TICTAC.ch8">TICTAC</a><br><a href="c8.html?38#ROM/TRON.ch8">TRON</a><br><a href="c8.html?39#ROM/UFO.ch8">UFO</a><br><a href="c8.html?40#ROM/VBRIX.ch8">VBRIX</a><br><a href="c8.html?41#ROM/VERS.ch8">VERS</a><br><a href="c8.html?42#ROM/WALL.ch8">WALL</a><br><a href="c8.html?43#ROM/WIPEOFF.ch8">WIPEOFF</a><br><br></div><style>*{text-indent:-9999;color:#fff;font-family:arial}h1,h2,div{color: #000;text-indent:0}a{color:blue}h1,h2,canvas{position:absolute;left:10px}canvas{overflow:hidden;top:100px;-webkit-transform:scale(4);transform:scale(4);-webkit-transform-origin:0 0;transform-origin:0 0}h1{top:0;text-indent:0}h2{top:40px;text-indent:0}div{position:absolute;top:250px}</style><script>
/** Initialization **/

// Vars
var imageData, audio, oscillator, i, memory, stack, pc, sp, I, timer, sound_timer, keys, keys_pressed, xhr, opcodes, tmp, opcode, interval, prefix, NNN, NN, N, X, Y, VX, VY, value, i, j, x, y;

// Canvas

// The context2D (C) already exists
imageData = (C = C.getContext("2d")).createImageData(64, 32);

// The canvas is white. The pixels are black. We just have to toggle their opacity to render black or white
for(i=64*32*4; i--;){
  imageData.data[i] = i%4-3 ? 0 : 255;
}

// Audio
audio = new (AudioContext = this.AudioContext || webkitAudioContext || 0);

// Memory
memory = [];

// Sprites of the characters 0-9,A-F (8*5px) are placed in the 160 first c8es of memory: 0xF0, 0x90, ...
for(i=80; i--;){
  memory[i] = eval("0x" + "F999F26227F1F8FF1F1F99F11F8F1FF8F9FF1244F9F9FF9F1FF9F99E9E9EF888FE999EF8F8FF8F88"[i] + "0");
}

// Registers
V = new Uint8Array(new ArrayBuffer(16));

// Stack
stack = [];

// Program counter
pc = 512;

// Stack pointer
sp = 0;

// Address register
I = 0;

// Timer
timer = 0;

// Sound timer
sound_timer = 0;

/** Detect keys pressed **/

// key map (keycodes to use for each chip8 key: numpad0-9 + QWERTY)
keys = [96,103,104,105,100,101,102,97,98,99,81,87,69,82,84,89];

// Keys currently pressed
keys_pressed = [];

/** Load ROM **/

xhr = new XMLHttpRequest;
xhr.open('GET', location.hash.slice(1));
xhr.responseType = 'arraybuffer';
xhr.send();
xhr.onload = function(){

  // Put ROM in memory
  for(i=(tmp = new Uint8Array(xhr.response)).length; i--;){
    memory[i+512] = tmp[i];
  }

  /** Loop **/
  interval = setInterval(function(){

    // Decrement the timers while > 0
    timer && timer--;
    sound_timer && sound_timer--;

    // Start sound if sound timer > 0
    if(audio && sound_timer && !oscillator){

      // New oscillator
      oscillator = audio.createOscillator();

      // Cross-browser start/stop
      if(!oscillator.start){
        oscillator.noteOn = oscillator.start;
      }
      if(!oscillator.stop){
        oscillator.noteOff = oscillator.stop;
      }

      // Start sound
      oscillator.connect(audio.destination);
      oscillator.type = 3;
      oscillator.start(0);
    }

    // Stop sound if sound timer == 0
    if(audio && !sound_timer && oscillator){
      oscillator.stop(0);
      oscillator = 0;
    }

    // Execute 4 opcodes
    for(opcodes = 4; opcodes--;){

      // Read opcode
      opcode = memory[pc] << 8 | memory[pc+1];
      //console.log("@"+pc + ": "+("00" + opcode.toString(16)).slice(-4));

      // Read opcode fields
      prefix = opcode >> 12;
      NNN = opcode & 0xFFF;
      NN = opcode & 0xFF;
      N = opcode & 0xF;
      X = opcode >> 8 & 0xF;
      VX = V[X];
      VY = V[opcode >> 4 & 0xF];

      // 00E0: clear
      if(opcode == 0xE0){
        for(i = 64*32*4; i--;){
          imageData.data[i] = i%4-3 ? 0 : 255;
        }
      }

      // 00EE: return from subprogram
      if(opcode == 0xEE){
        pc = stack.pop();
      }

      // 1NNN: jump to NNN
      if(prefix == 1){
        pc = NNN - 2;
      }

      // 2NNN: call subprogram at NNN
      if(prefix == 2){
        stack.push(pc);
        pc = NNN - 2;
      }

      // 3XNN: ignore next opcode if VX == NN
      // 4XNN: ignore next opcode if VX != NN
      // 5XY0: ignore next opcode if VX == VY
      // 9XY0: ignore next opcode if VX != VY
      // EX9E: ignore next opcode if VX is pressed
      // EXA1: ignore next opcode if VX is not pressed
      if((prefix == 3 && VX == NN)
      || (prefix == 4 && VX != NN)
      || (prefix == 5 && VX == VY)
      || (prefix == 9 && VX != VY)
      || (prefix == 0xE && ((NN == 0x9E && keys_pressed[VX]) || (NN == 0xA1 && !keys_pressed[VX])))
      ){
        pc += 2;
      }

      // 6XNN: set VX to NN
      if(prefix == 6){
        V[X] = NN;
      }

      // 7XNN: add NN to VX
      if(prefix == 7){
        V[X] = VX + NN;
      }

      // 8XYN:
      if(prefix == 8){

        // 8XY0: set VX to VY
        if(!N){
          V[X] = VY;
        }

        // 8XY1: set VX to VX OR VY
        if(N == 1){
          V[X] |= VY;
        }

        // 8XY2: set VX to VX AND VY
        if(N == 2){
          V[X] &= VY;
        }

        // 8XY3: set VX to VX XOR VY
        if(N == 3){
          V[X] ^= VY;
        }

        // 8XY4: add VY to VX, put carry in VF
        if(N == 4){
          V[0xF] = +((V[X] += VY) > 0xFF);
        }

        // 8XY5: substract VY to VX, put NOT borrow in VF
        if(N == 5){
          V[0xF] = +((V[X] -= VY) >= 0);
        }

        // 8XY6: right shift VX, put shifted bit in VF
        if(N == 6){
          V[0xF] = VX & 0x1;
          V[X] /= 2;
        }

        // 8XY7: VX = VY - VX, put NOT borrow in VF
        if(N == 7){
          V[0xF] = +((V[X] = VY - VX) >= 0);
        }

        // 8XYE: left shift VX, put shifted bit in VF
        if(N == 0xE){
          V[0xF] = VX >> 7;
          V[X] *= 2;
        }
      }

      // ANNN: set I to NNN
      if(prefix == 0xA){
        I = NNN;
      }

      // BNNN: jump to NNN + V0
      if(prefix == 0xB){
        pc = NNN + V[0];
      }

      // CXNN: set VX to a random number < NN
      if(prefix == 0xC){
        V[X] = Math.floor(Math.random() * NN);
      }

      // DXYN: draw the 8*N px sprite stored at address I at coordinates [X:Y]
      if(prefix == 0xD){

        V[0xF] = 0;

        // Loop on the N lines of the sprite
        for(i = N; i--;){

          // Loop on the 8 pixels of the current line of the sprite
          for(j = 8; j--;){

            // Get the value of the pixel
            value = (memory[I+i]>>(7-j))&0x1;

            // Get the coordinates of the pixel
            x = VX + j;
            y = VY + i;

            // If the pixel is on
            if(value){

              // If the pixel is out of bounds, wrap
              if(x > 63){
                x -= 63;
              }

              if(y > 31){
                y -= 31;
              }

              // If the pixel is already white (opacity == 0), make it black and set VF to 1. Else, make it white.
              tmp = 4*(64*y+x)+3;
              if(imageData.data[tmp]){
                imageData.data[tmp] = 0;
              }
              else{
                imageData.data[tmp] = 255;
                V[0xF] = 1;
              }
            }
          }
        }
      }

      // FXNN:
      if(prefix == 0xF){

        // FX07: set VX to the timer value
        if(NN == 0x07){
          V[X] = timer;
        }

        // FX0A: prompt, store key pressed in VX
        if(NN == 0x0A){

          // Loop until VX != -1
          if(!~(V[X] = keys_pressed.c8Of(!0))){
            pc -= 2;
          }
        }

        // FX15: set timer to VX
        if(NN == 0x15){
          timer = VX;
        }

        // FX18: set sound timer to VX
        if(NN == 0x18){
          sound_timer = VX;
        }

        // FX1E: add VX to I, set VF to I's overflow (I>0xFFF)
        if(NN == 0x1E){
          I += VX;
          V[0xF] = +(I > 0xFFF);
          I &= 0xFFF;
        }

        // FX29: set I to the character VX
        if(NN == 0x29){
          I = VX * 5;
        }

        // FX33: store the decimal value of VX in memory at address I (hundreds), I+1 (dozens), I+2 (units)
        if(NN == 0x33){
          for(i = 3; i--;){
            memory[I+i]=(""+VX)[i];
          }
        }

        // FX55: store V0 to VX in memory from address I
        if(NN == 0x55){
          for(i = X; i--;){
            memory[I + i] = V[i];
          }
        }

        // FX65: load V0 to VX from memory at address I
        if(NN == 0x65){
          for(i = X; i--;){
            V[i] = memory[I + i];
          }
        }
      }

      // Next instruction
      pc += 2;
    }

    // Refresh screen
    C.putImageData(imageData, 0, 0);

  },16);
}

onkeydown = function(e){
  keys_pressed[keys.indexOf(e.keyCode)] = !0;
}

onkeyup = function(e){
  keys_pressed[keys.indexOf(e.keyCode)] = !1;
}
</script>