public void draw(int x, int y, int n)
{
registers[0x0F] = 0;
for (int dY = 0; dY < n; dY++)
{
ushort location = (ushort)(I + dY);
byte pixel = Chip8Memory.memory[location];
for (int dX = 0; dX < 8; dX++)
{
int offset = ((y + dY) * Chip8Display.SCREEN_WIDTH) + x + dX;
if ((pixel & (0x80 >> dX)) != 0)
{
if (Chip8Display.isWhite(offset))
{
registers[0x0F] = 1;
}
bool isWhite = Chip8Display.isWhite(offset) ^ true;
Chip8Display.draw(offset, isWhite);
}
}
}
}
public void executeInstruction()
{
byte byte1 = Chip8Memory.memory[Chip8InstructionPointer.offset++];
byte byte2 = Chip8Memory.memory[Chip8InstructionPointer.offset++];
byte registerX = registers[Chip8Opcode.getX(byte1)];
byte registerY = registers[Chip8Opcode.getY(byte2)];
byte value;
switch (Chip8Opcode.getCode(byte1))
{
case 0x00:
switch (Chip8Opcode.getNN(byte2))
{
case 0xE0:
Chip8Display.clear();
break;
case 0xEE:
byte returnByte1 = Chip8Memory.memory[--Chip8StackPointer.offset];
byte returnByte2 = Chip8Memory.memory[--Chip8StackPointer.offset];
Chip8InstructionPointer.offset = (ushort)((returnByte1 << 8) + returnByte2);
break;
default:
throw new IllegalChip8OpcodeException("Illegal Opcode " + byte1.ToString("X2") + byte2.ToString("X2"));
}
break;
case 0x01:
Chip8InstructionPointer.offset = Chip8Opcode.getNNN(byte1, byte2);
break;
case 0x02:
Chip8Memory.memory[Chip8StackPointer.offset++] = (byte)(Chip8InstructionPointer.offset & 0x0F);
Chip8Memory.memory[Chip8StackPointer.offset++] = (byte)(Chip8InstructionPointer.offset >> 8);
Chip8InstructionPointer.offset = Chip8Opcode.getNNN(byte1, byte2);
break;
case 0x03:
if (registerX == Chip8Opcode.getNN(byte2))
{
Chip8InstructionPointer.increment();
}
break;
case 0x04:
if (registerX != Chip8Opcode.getNN(byte2))
{
Chip8InstructionPointer.increment();
}
break;
case 0x05:
if (registerX == registerY)
{
Chip8InstructionPointer.increment();
}
break;
case 0x06:
registers[Chip8Opcode.getX(byte1)] = Chip8Opcode.getNN(byte2);
break;
case 0x07:
value = (byte)(registerX + Chip8Opcode.getNN(byte2));
registers[Chip8Opcode.getX(byte1)] = value;
break;
case 0x08:
switch (Chip8Opcode.getN(byte2))
{
case 0x00:
registers[Chip8Opcode.getX(byte1)] = registerY;
break;
case 0x01:
value = (byte)(registerX | registerY);
registers[Chip8Opcode.getX(byte1)] = value;
break;
case 0x02:
value = (byte)(registerX & registerY);
registers[Chip8Opcode.getX(byte1)] = value;
break;
case 0x03:
value = (byte)(registerX ^ registerY);
registers[Chip8Opcode.getX(byte1)] = value;
break;
case 0x04:
// handle VF
value = (byte)(registerX + registerY);
registers[Chip8Opcode.getX(byte1)] = value;
break;
case 0x05:
//handle VF
value = (byte)(registerX - registerY);
registers[Chip8Opcode.getX(byte1)] = value;
break;
case 0x06:
//handle VF
value = (byte)(registerY >> 1);
registers[Chip8Opcode.getX(byte1)] = value;
break;
case 0x07:
//handle VF
value = (byte)(registerY - registerX);
registers[Chip8Opcode.getX(byte1)] = value;
break;
case 0x0E:
//handle VF
value = (byte)(registerY << 1);
registers[Chip8Opcode.getX(byte1)] = value;
registers[Chip8Opcode.getY(byte2)] = value;
break;
default:
throw new IllegalChip8OpcodeException("Illegal Opcode " + byte1.ToString("X2") + byte2.ToString("X2"));
}
break;
case 0x09:
if (registerX != registerY)
{
Chip8InstructionPointer.increment();
}
break;
case 0x0A:
I = Chip8Opcode.getNNN(byte1, byte2);
break;
case 0x0B:
ushort offset = (ushort)(registers[0] + Chip8Opcode.getNNN(byte1, byte2));
Chip8InstructionPointer.offset = offset;
break;
case 0x0C:
value = (byte)(random.Next(256) & Chip8Opcode.getNN(byte2));
registers[Chip8Opcode.getX(byte1)] = value;
break;
case 0x0D:
int x = registerX;
int y = registerY;
int n = Chip8Opcode.getN(byte2);
draw(x, y, n);
break;
case 0x0E:
switch (Chip8Opcode.getNN(byte2))
{
case 0x9E:
if (keyboard.keyState[Chip8Opcode.getX(byte1)])
{
Chip8InstructionPointer.increment();
}
break;
case 0xA1:
if (!keyboard.keyState[Chip8Opcode.getX(byte1)])
{
Chip8InstructionPointer.increment();
}
break;
default:
throw new IllegalChip8OpcodeException("Illegal Opcode " + byte1.ToString("X2") + byte2.ToString("X2"));
}
break;
case 0x0F:
switch (Chip8Opcode.getNN(byte2))
{
case 0x07:
registers[Chip8Opcode.getX(byte1)] = (byte)delayTimer.get();
break;
case 0x0A:
// TODO: implment readkey
registers[Chip8Opcode.getX(byte1)] = 0; // should be read key
break;
case 0x15:
delayTimer.set(registerX);
break;
case 0x18:
soundTimer.set(registerX);
break;
case 0x1E:
I += registerX;
break;
case 0x29:
I = (byte)(Chip8Fontset.FONT_HEIGHT * registerX);
break;
case 0x33:
Chip8Memory.memory[I] = (byte)(registerX / 100);
Chip8Memory.memory[I + 1] = (byte)((registerX % 100) / 10);
Chip8Memory.memory[I + 2] = (byte)(registerX % 10);
break;
case 0x55:
for (int i = 0; i <= Chip8Opcode.getX(byte1); i++)
{
Chip8Memory.memory[I++] = registers[i];
}
break;
case 0x65:
for (int i = 0; i <= Chip8Opcode.getX(byte1); i++)
{
registers[i] = Chip8Memory.memory[I++];
}
break;
default:
throw new IllegalChip8OpcodeException("Illegal Opcode " + byte1.ToString("X2") + byte2.ToString("X2"));
}
break;
default:
throw new IllegalChip8OpcodeException("Illegal Opcode " + byte1.ToString("X2") + byte2.ToString("X2"));
}
}