public PPU(Cpu cpu, Cartridge cartridge, IDisplay display, Nes nes)
{
_nes = nes;
_display = display;
_cpu = cpu;
_cartridge = cartridge;
for (int i = 0; i < 64; i++)
{
Oam[i] = new Oam();
}
}
public void Clock()
{
if (_scanline >= -1 && _scanline < 240)
{
if (_scanline == 0 && _cycle == 0)
{
_cycle = 1;
}
else if (_scanline == -1 && _cycle == 1)
{
PPURegisters.PPUSTATUS.VerticalBlank = false;
// Clear Shifters
for (int i = 0; i < 8; i++)
{
_spriteShifterPatternLow[i] = 0;
_spriteShifterPatternHigh[i] = 0;
PPURegisters.PPUSTATUS.SpriteOverflow = false;
PPURegisters.PPUSTATUS.SpriteHit = false;
}
}
else if ((_cycle >= 2 && _cycle < 258) || (_cycle >= 321 && _cycle < 338))
{
UpdateShifters();
switch ((_cycle - 1) % 8)
{
case 0:
LoadBgShifters();
_bgNextTileId = ReadPpu(NAMETABLE | (_vram.Value & 0x0FFF));
break;
case 2:
_bgNextTileAttr = ReadPpu(NAMETABLE_ATTRIBUTES | (_vram.NametableY << 11)
| (_vram.NametableX << 10)
| ((_vram.CoarseY >> 2) << 3)
| (_vram.CoarseX >> 2));
if ((_vram.CoarseY & 0x02) != 0)
{
_bgNextTileAttr >>= 4;
}
if ((_vram.CoarseX & 0x02) != 0)
{
_bgNextTileAttr >>= 2;
}
_bgNextTileAttr &= 0x03;
break;
case 4:
_bgNextTileLo = ReadPpu(((PPURegisters.PPUCTRL.PatternBackground ? 1 : 0) << 12)
+ (_bgNextTileId << 4) + _vram.FineY);
break;
case 6:
_bgNextTileHi = ReadPpu(((PPURegisters.PPUCTRL.PatternBackground ? 1 : 0) << 12)
+ (_bgNextTileId << 4) + (_vram.FineY) + 8);
break;
case 7:
IncrementScrollX();
break;
default:
break;
}
}
if (_cycle == 256)
{
IncrementScrollY();
}
else if (_cycle == 257)
{
LoadBgShifters();
TransferAddressX();
}
else if (_cycle == 338 || _cycle == 340)
{
_bgNextTileId = ReadPpu(NAMETABLE | (_vram.Value & 0x0FFF));
}
else if (_scanline == -1 && _cycle >= 280 && _cycle < 305)
{
TransferAddressY();
}
if (_cycle == 257 && _scanline >= 0)
{
for (int i = 0; i < 8; i++)
{
_spriteScanline[i] = new Oam();
}
_spriteCount = 0;
for (int i = 0; i < 8; i++)
{
_spriteShifterPatternLow[i] = 0;
_spriteShifterPatternHigh[i] = 0;
}
byte index = 0;
_spriteZeroHitPossible = false;
while (index < 64 && _spriteCount < 9)
{
int diff = _scanline - Oam[index].Y;
if (diff >= 0 && diff < (PPURegisters.PPUCTRL.SpriteHeight ? 16 : 8))
{
if (_spriteCount < 8)
{
if (index == 0)
{
_spriteZeroHitPossible = true;
}
_spriteScanline[_spriteCount] = Oam[index];
_spriteCount++;
}
}
index++;
}
PPURegisters.PPUSTATUS.SpriteOverflow = (_spriteCount > 8);
}
if (_cycle == 340)
{
for (byte i = 0; i < _spriteCount; i++)
{
byte spritePatternBitsLo, spritePatternBitsHi;
ushort spritePatternAddrLo, spritePatternAddrHi;
if (!PPURegisters.PPUCTRL.SpriteHeight)
{
if ((_spriteScanline[i].Attributes & 0x80) == 0)
{
spritePatternAddrLo = (ushort)(
((PPURegisters.PPUCTRL.PatternSprite ? 1 : 0) << 12)
| (_spriteScanline[i].Id << 4)
| (_scanline - _spriteScanline[i].Y));
}
else
{
spritePatternAddrLo = (ushort)(
((PPURegisters.PPUCTRL.PatternSprite ? 1 : 0) << 12)
| (_spriteScanline[i].Id << 4)
| (7 - (_scanline - _spriteScanline[i].Y)));
}
}
else
{
if ((_spriteScanline[i].Attributes & 0x80) == 0)
{
if (_scanline - _spriteScanline[i].Y < 8)
{
spritePatternAddrLo = (ushort)(
((_spriteScanline[i].Id & 0x01) << 12)
| ((_spriteScanline[i].Id & 0xFE) << 4)
| ((_scanline - _spriteScanline[i].Y) & 0x07));
}
else
{
spritePatternAddrLo = (ushort)(
((_spriteScanline[i].Id & 0x01) << 12)
| (((_spriteScanline[i].Id & 0xFE) + 1) << 4)
| ((_scanline - _spriteScanline[i].Y) & 0x07));
}
}
else
{
if (_scanline - _spriteScanline[i].Y < 8)
{
spritePatternAddrLo = (ushort)(
((_spriteScanline[i].Id & 0x01) << 12)
| (((_spriteScanline[i].Id & 0xFE) + 1) << 4)
| (7 - (_scanline - _spriteScanline[i].Y) & 0x07));
}
else
{
spritePatternAddrLo = (ushort)(((_spriteScanline[i].Id & 0x01) << 12)
| ((_spriteScanline[i].Id & 0xFE) << 4)
| (7 - (_scanline - _spriteScanline[i].Y) & 0x07));
}
}
}
spritePatternAddrHi = (ushort)(spritePatternAddrLo + 8);
spritePatternBitsLo = ReadPpu(spritePatternAddrLo);
spritePatternBitsHi = ReadPpu(spritePatternAddrHi);
if ((_spriteScanline[i].Attributes & 0x40) > 0)
{
spritePatternBitsLo = FlipByte(spritePatternBitsLo);
spritePatternBitsHi = FlipByte(spritePatternBitsHi);
}
_spriteShifterPatternLow[i] = spritePatternBitsLo;
_spriteShifterPatternHigh[i] = spritePatternBitsHi;
}
}
}
else if (_scanline == 240)
{
//do nothing
}
else if (_scanline == 241 && _cycle == 1)
{
//First pixel of the nonvisible scanline
PPURegisters.PPUSTATUS.VerticalBlank = true;
if (PPURegisters.PPUCTRL.NmiEnabled)
{
_cpu.Nmi();
}
}
if (_cycle > 0 && _scanline >= 0 && _cycle - 1 < 256 && _scanline < 240)
{
byte bg_pixel = 0x00;
byte bg_palette = 0x00;
if (PPURegisters.PPUMASK.BackgroundEnable)
{
var bit_mux = (ushort)(0x8000 >> _fineX);
var p0_pixel = (_bgShifterPatternLo & bit_mux) != 0 ? 1 : 0;
var p1_pixel = (_bgShifterPatternHi & bit_mux) != 0 ? 1 : 0;
bg_pixel = (byte)((p1_pixel << 1) | p0_pixel);
var bg_pal0 = (_bgShifterAttributeLo & bit_mux) != 0 ? 1 : 0;
var bg_pal1 = (_bgShifterAttributeHi & bit_mux) != 0 ? 1 : 0;
bg_palette = (byte)((bg_pal1 << 1) | bg_pal0);
}
byte fg_pixel = 0x00;
byte fg_palette = 0x00;
byte fg_priority = 0x00;
if (PPURegisters.PPUMASK.SpriteEnable)
{
_spriteZeroBeingRendered = false;
for (byte i = 0; i < _spriteCount; i++)
{
if (_spriteScanline[i].X == 0)
{
byte fg_pixel_lo = (byte)((_spriteShifterPatternLow[i] & 0x80) > 0 ? 1 : 0);
byte fg_pixel_hi = (byte)((_spriteShifterPatternHigh[i] & 0x80) > 0 ? 1 : 0);
fg_pixel = (byte)((fg_pixel_hi << 1) | fg_pixel_lo);
fg_palette = (byte)((_spriteScanline[i].Attributes & 0x03) + 0x04);
fg_priority = (byte)((_spriteScanline[i].Attributes & 0x20) == 0 ? 1 : 0);
if (fg_pixel != 0)
{
if (i == 0)
{
_spriteZeroBeingRendered = true;
}
break;
}
}
}
}
byte pixel = 0x00;
byte palette = 0x00;
if (bg_pixel == 0 && fg_pixel == 0)
{
pixel = 0x00;
palette = 0x00;
}
else if (bg_pixel == 0 && fg_pixel > 0)
{
pixel = fg_pixel;
palette = fg_palette;
}
else if (bg_pixel > 0 && fg_pixel == 0)
{
pixel = bg_pixel;
palette = bg_palette;
}
else if (bg_pixel > 0 && fg_pixel > 0)
{
if (fg_priority == 1)
{
pixel = fg_pixel;
palette = fg_palette;
}
else
{
pixel = bg_pixel;
palette = bg_palette;
}
if (_spriteZeroHitPossible && _spriteZeroBeingRendered)
{
if (PPURegisters.PPUMASK.SpriteEnable && PPURegisters.PPUMASK.BackgroundEnable)
{
if (!(PPURegisters.PPUMASK.BackgroundLeftColumnEnable || PPURegisters.PPUMASK.SpriteLeftColumnEnable))
{
if (_cycle >= 9 && _cycle < 258)
{
PPURegisters.PPUSTATUS.SpriteHit = true;
}
}
else
{
if (_cycle >= 1 && _cycle < 258)
{
PPURegisters.PPUSTATUS.SpriteHit = true;
}
}
}
}
}
_display.DrawPixel(_cycle - 1, _scanline, GetColorFromPalette(palette, pixel));
if (_nes.SuperSlow > 0 && _cycle > 2 && _cycle < 256)
{
_display.DrawPixel((_cycle - 1 + 1) % 256, _scanline, 0xFF00fF);
}
}
_cycle++;
if (_cycle >= 341)
{
_cycle = 0;
_scanline++;
if (_scanline >= 261)
{
_scanline = -1;
FrameFinished = true;
_display.SetFrameFinished();
}
}
}
