internal void Step(uint instructionTime)
{
if (!LCDC.HasFlag(LCDC.LCDEnable))
{
return;
}
_modeClock += instructionTime;
GPUMode mode = Mode;
switch (mode)
{
case GPUMode.Mode0: // HBlank
Mode0();
break;
case GPUMode.Mode1: // VBlank
Mode1();
break;
case GPUMode.Mode2: // OAM
Mode2();
break;
case GPUMode.Mode3: // LCD Transfer
Mode3();
break;
default:
break;
}
}
public override string ToString()
{
return(String.Format("{0}{1}Scanline: {2}{3}Window X,Y: {4} , {5}{6}BG Scroll X, Y: {7} , {8}{9}",
LCDC.ToString(),
STAT.ToString(),
ppu.CurrentScanline, Environment.NewLine,
WindowX, WindowY, Environment.NewLine,
BgScrollX, BgScrollY, Environment.NewLine));
}
public override void process_sprite()
{
int y;
if (SL_sprites[sl_use_index * 4 + 3].Bit(6))
{
if (LCDC.Bit(2))
{
y = LY - (SL_sprites[sl_use_index * 4] - 16);
y = 15 - y;
sprite_sel[0] = Core.VRAM[(SL_sprites[sl_use_index * 4 + 2] & 0xFE) * 16 + y * 2];
sprite_sel[1] = Core.VRAM[(SL_sprites[sl_use_index * 4 + 2] & 0xFE) * 16 + y * 2 + 1];
}
else
{
y = LY - (SL_sprites[sl_use_index * 4] - 16);
y = 7 - y;
sprite_sel[0] = Core.VRAM[SL_sprites[sl_use_index * 4 + 2] * 16 + y * 2];
sprite_sel[1] = Core.VRAM[SL_sprites[sl_use_index * 4 + 2] * 16 + y * 2 + 1];
}
}
else
{
if (LCDC.Bit(2))
{
y = LY - (SL_sprites[sl_use_index * 4] - 16);
sprite_sel[0] = Core.VRAM[(SL_sprites[sl_use_index * 4 + 2] & 0xFE) * 16 + y * 2];
sprite_sel[1] = Core.VRAM[(SL_sprites[sl_use_index * 4 + 2] & 0xFE) * 16 + y * 2 + 1];
}
else
{
y = LY - (SL_sprites[sl_use_index * 4] - 16);
sprite_sel[0] = Core.VRAM[SL_sprites[sl_use_index * 4 + 2] * 16 + y * 2];
sprite_sel[1] = Core.VRAM[SL_sprites[sl_use_index * 4 + 2] * 16 + y * 2 + 1];
}
}
if (SL_sprites[sl_use_index * 4 + 3].Bit(5))
{
int b0, b1, b2, b3, b4, b5, b6, b7 = 0;
for (int i = 0; i < 2; i++)
{
b0 = (sprite_sel[i] & 0x01) << 7;
b1 = (sprite_sel[i] & 0x02) << 5;
b2 = (sprite_sel[i] & 0x04) << 3;
b3 = (sprite_sel[i] & 0x08) << 1;
b4 = (sprite_sel[i] & 0x10) >> 1;
b5 = (sprite_sel[i] & 0x20) >> 3;
b6 = (sprite_sel[i] & 0x40) >> 5;
b7 = (sprite_sel[i] & 0x80) >> 7;
sprite_sel[i] = (byte)(b0 | b1 | b2 | b3 | b4 | b5 | b6 | b7);
}
}
}
private ReadOnlySpan <byte> GetSelectedBackgroundTileMap()
{
if (LCDC.HasFlag(LCDC.BGTileMapSelect))
{
return(BackgroundMap1);
}
else
{
return(BackgroundMap0);
}
}
private void Scanline()
{
int line = LY;
var frameLine = _frame.AsSpan(line * 256, 256);
ReadOnlySpan <byte> windowTileMap = GetSelectedWindowTileMap();
ReadOnlySpan <byte> bgTileMap = GetSelectedBackgroundTileMap();
ReadOnlySpan <BGTile> bgTileData = SelectedBackgroundTileData;
bool isWindowDisplayEnabled = LCDC.HasFlag(LCDC.WindowDisplayEnabled);
var tileMapSliced = bgTileMap.Slice(line / 8 * 32, 32);
if (isWindowDisplayEnabled)
{
// TODO : Draw the window over
}
}
public override void render(int render_cycle)
{
// we are now in STAT mode 3
// NOTE: presumably the first necessary sprite is fetched at sprite evaulation
// i.e. just keeping track of the lowest x-value sprite
if (render_cycle == 0)
{
OAM_access_read = false;
OAM_access_write = true;
VRAM_access_read = false;
// window X is latched for the scanline, mid-line changes have no effect
window_x_latch = window_x;
OAM_scan_index = 0;
read_case = 0;
internal_cycle = 0;
pre_render = true;
tile_inc = 0;
pixel_counter = -8;
sl_use_index = 0;
fetch_sprite = false;
fetch_sprite_01 = false;
fetch_sprite_4 = false;
going_to_fetch = false;
first_fetch = true;
no_sprites = false;
evaled_sprites = 0;
window_pre_render = false;
window_latch = LCDC.Bit(5);
// TODO: If Window is turned on midscanline what happens? When is this check done exactly?
if ((window_started && window_latch) || (window_is_reset && !window_latch && (LY > window_y)))
{
window_y_tile_inc++;
if (window_y_tile_inc == 8)
{
window_y_tile_inc = 0;
window_y_tile++;
window_y_tile %= 32;
}
}
window_started = false;
if (SL_sprites_index == 0)
{
no_sprites = true;
}
// it is much easier to process sprites if we order them according to the rules of sprite priority first
if (!no_sprites)
{
reorder_and_assemble_sprites();
}
}
// before anything else, we have to check if windowing is in effect
if (window_latch && !window_started && (LY >= window_y) && (pixel_counter >= (window_x_latch - 7)) && (window_x_latch < 167))
{
/*
* Console.Write(LY);
* Console.Write(" ");
* Console.Write(cycle);
* Console.Write(" ");
* Console.Write(window_y_tile_inc);
* Console.Write(" ");
* Console.Write(window_x_latch);
* Console.Write(" ");
* Console.WriteLine(pixel_counter);
*/
if (window_x_latch <= 7)
{
// if the window starts at zero, we still do the first access to the BG
// but then restart all over again at the window
read_case = 9;
}
else
{
// otherwise, just restart the whole process as if starting BG again
read_case = 4;
}
window_pre_render = true;
window_counter = 0;
render_counter = 0;
window_x_tile = (int)Math.Floor((float)(pixel_counter - (window_x_latch - 7)) / 8);
window_tile_inc = 0;
window_started = true;
window_is_reset = false;
}
if (!pre_render && !fetch_sprite)
{
// start shifting data into the LCD
if (render_counter >= (render_offset + 8))
{
pixel = tile_data_latch[0].Bit(7 - (render_counter % 8)) ? 1 : 0;
pixel |= tile_data_latch[1].Bit(7 - (render_counter % 8)) ? 2 : 0;
int ref_pixel = pixel;
if (LCDC.Bit(0))
{
pixel = (BGP >> (pixel * 2)) & 3;
}
else
{
pixel = 0;
}
// now we have the BG pixel, we next need the sprite pixel
if (!no_sprites)
{
bool have_sprite = false;
int s_pixel = 0;
int sprite_attr = 0;
if (sprite_present_list[pixel_counter] == 1)
{
have_sprite = true;
s_pixel = sprite_pixel_list[pixel_counter];
sprite_attr = sprite_attr_list[pixel_counter];
}
if (have_sprite)
{
bool use_sprite = false;
if (LCDC.Bit(1))
{
if (!sprite_attr.Bit(7))
{
use_sprite = true;
}
else if (ref_pixel == 0)
{
use_sprite = true;
}
if (!LCDC.Bit(0))
{
use_sprite = true;
}
}
if (use_sprite)
{
if (sprite_attr.Bit(4))
{
pixel = (obj_pal_1 >> (s_pixel * 2)) & 3;
}
else
{
pixel = (obj_pal_0 >> (s_pixel * 2)) & 3;
}
}
}
}
// based on sprite priority and pixel values, pick a final pixel color
Core._vidbuffer[LY * 160 + pixel_counter] = (int)Core.color_palette[pixel];
pixel_counter++;
if (pixel_counter == 160)
{
read_case = 8;
hbl_countdown = 5;
}
}
else if (pixel_counter < 0)
{
pixel_counter++;
}
render_counter++;
}
if (!fetch_sprite)
{
if (!pre_render)
{
// before we go on to read case 3, we need to know if we stall there or not
// Gekkio's tests show that if sprites are at position 0 or 1 (mod 8)
// then it takes an extra cycle (1 or 2 more t-states) to process them
if (!no_sprites && (pixel_counter < 160))
{
for (int i = 0; i < SL_sprites_index; i++)
{
if ((pixel_counter >= (SL_sprites[i * 4 + 1] - 8)) &&
(pixel_counter < (SL_sprites[i * 4 + 1])) &&
!evaled_sprites.Bit(i))
{
going_to_fetch = true;
fetch_sprite = true;
if ((SL_sprites[i * 4 + 1] % 8) < 2)
{
fetch_sprite_01 = true;
}
if ((SL_sprites[i * 4 + 1] % 8) > 3)
{
fetch_sprite_4 = true;
}
}
}
}
}
switch (read_case)
{
case 0: // read a background tile
if ((internal_cycle % 2) == 0)
{
// calculate the row number of the tiles to be fetched
y_tile = ((int)Math.Floor((float)(scroll_y + LY) / 8)) % 32;
temp_fetch = y_tile * 32 + (x_tile + tile_inc) % 32;
tile_byte = Core.VRAM[0x1800 + (LCDC.Bit(3) ? 1 : 0) * 0x400 + temp_fetch];
}
else
{
read_case = 1;
if (!pre_render)
{
tile_inc++;
}
}
break;
case 1: // read from tile graphics (0)
if ((internal_cycle % 2) == 0)
{
y_scroll_offset = (scroll_y + LY) % 8;
if (LCDC.Bit(4))
{
tile_data[0] = Core.VRAM[tile_byte * 16 + y_scroll_offset * 2];
}
else
{
// same as before except now tile byte represents a signed byte
if (tile_byte.Bit(7))
{
tile_byte -= 256;
}
tile_data[0] = Core.VRAM[0x1000 + tile_byte * 16 + y_scroll_offset * 2];
}
}
else
{
read_case = 2;
}
break;
case 2: // read from tile graphics (1)
if ((internal_cycle % 2) == 0)
{
y_scroll_offset = (scroll_y + LY) % 8;
if (LCDC.Bit(4))
{
// if LCDC somehow changed between the two reads, make sure we have a positive number
if (tile_byte < 0)
{
tile_byte += 256;
}
tile_data[1] = Core.VRAM[tile_byte * 16 + y_scroll_offset * 2 + 1];
}
else
{
// same as before except now tile byte represents a signed byte
if (tile_byte.Bit(7) && tile_byte > 0)
{
tile_byte -= 256;
}
tile_data[1] = Core.VRAM[0x1000 + tile_byte * 16 + y_scroll_offset * 2 + 1];
}
}
else
{
if (pre_render)
{
// here we set up rendering
pre_render = false;
render_offset = scroll_x % 8;
render_counter = 0;
latch_counter = 0;
read_case = 0;
}
else
{
read_case = 3;
}
}
break;
case 3: // read from sprite data
if ((internal_cycle % 2) == 0)
{
// nothing to do if not fetching
}
else
{
read_case = 0;
latch_new_data = true;
}
break;
case 4: // read from window data
if ((window_counter % 2) == 0)
{
temp_fetch = window_y_tile * 32 + (window_x_tile + window_tile_inc) % 32;
tile_byte = Core.VRAM[0x1800 + (LCDC.Bit(6) ? 1 : 0) * 0x400 + temp_fetch];;
}
else
{
window_tile_inc++;
read_case = 5;
}
window_counter++;
break;
case 5: // read from tile graphics (for the window)
if ((window_counter % 2) == 0)
{
y_scroll_offset = (window_y_tile_inc) % 8;
if (LCDC.Bit(4))
{
tile_data[0] = Core.VRAM[tile_byte * 16 + y_scroll_offset * 2];
}
else
{
// same as before except now tile byte represents a signed byte
if (tile_byte.Bit(7))
{
tile_byte -= 256;
}
tile_data[0] = Core.VRAM[0x1000 + tile_byte * 16 + y_scroll_offset * 2];
}
}
else
{
read_case = 6;
}
window_counter++;
break;
case 6: // read from tile graphics (for the window)
if ((window_counter % 2) == 0)
{
y_scroll_offset = (window_y_tile_inc) % 8;
if (LCDC.Bit(4))
{
// if LCDC somehow changed between the two reads, make sure we have a positive number
if (tile_byte < 0)
{
tile_byte += 256;
}
tile_data[1] = Core.VRAM[tile_byte * 16 + y_scroll_offset * 2 + 1];
}
else
{
// same as before except now tile byte represents a signed byte
if (tile_byte.Bit(7) && tile_byte > 0)
{
tile_byte -= 256;
}
tile_data[1] = Core.VRAM[0x1000 + tile_byte * 16 + y_scroll_offset * 2 + 1];
}
}
else
{
if (window_pre_render)
{
// here we set up rendering
// unlike for the normal background case, there is no pre-render period for the window
// so start shifting in data to the screen right away
render_offset = 0;
render_counter = 8;
latch_counter = 0;
latch_new_data = true;
window_pre_render = false;
read_case = 4;
}
else
{
read_case = 7;
}
}
window_counter++;
break;
case 7: // read from sprite data
if ((window_counter % 2) == 0)
{
// nothing to do if not fetching
}
else
{
read_case = 4;
latch_new_data = true;
}
window_counter++;
break;
case 8: // done reading, we are now in phase 0
pre_render = true;
// the other interrupts appear to be delayed by 1 CPU cycle, so do the same here
if (hbl_countdown > 0)
{
hbl_countdown--;
if (hbl_countdown == 0)
{
STAT &= 0xFC;
STAT |= 0x00;
if (STAT.Bit(3))
{
HBL_INT = true;
}
OAM_access_read = true;
OAM_access_write = true;
VRAM_access_read = true;
VRAM_access_write = true;
}
}
break;
case 9:
// this is a degenerate case for starting the window at 0
// kevtris' timing doc indicates an additional normal BG access
// but this information is thrown away, so it's faster to do this then constantly check
// for it in read case 0
read_case = 4;
break;
}
internal_cycle++;
if (latch_new_data)
{
latch_new_data = false;
tile_data_latch[0] = tile_data[0];
tile_data_latch[1] = tile_data[1];
}
}
// every in range sprite takes 6 cycles to process
// sprites located at x=0 still take 6 cycles to process even though they don't appear on screen
// sprites above x=168 do not take any cycles to process however
if (fetch_sprite)
{
if (going_to_fetch)
{
going_to_fetch = false;
sprite_fetch_counter = first_fetch ? 2 : 0;
first_fetch = false;
if (fetch_sprite_01)
{
sprite_fetch_counter += 2;
fetch_sprite_01 = false;
}
if (fetch_sprite_4)
{
sprite_fetch_counter -= 2;
fetch_sprite_4 = false;
}
int last_eval = 0;
// at this time it is unknown what each cycle does, but we only need to accurately keep track of cycles
for (int i = 0; i < SL_sprites_index; i++)
{
if ((pixel_counter >= (SL_sprites[i * 4 + 1] - 8)) &&
(pixel_counter < (SL_sprites[i * 4 + 1])) &&
!evaled_sprites.Bit(i))
{
sprite_fetch_counter += 6;
evaled_sprites |= (1 << i);
last_eval = SL_sprites[i * 4 + 1];
}
}
// if we didn't evaluate all the sprites immediately, 2 more cycles are added to restart it
if (evaled_sprites != (Math.Pow(2, SL_sprites_index) - 1))
{
if ((last_eval % 8) == 0)
{
sprite_fetch_counter += 3;
}
else if ((last_eval % 8) == 1)
{
sprite_fetch_counter += 2;
}
else if ((last_eval % 8) == 2)
{
sprite_fetch_counter += 3;
}
else if ((last_eval % 8) == 3)
{
sprite_fetch_counter += 2;
}
else if ((last_eval % 8) == 4)
{
sprite_fetch_counter += 3;
}
else
{
sprite_fetch_counter += 2;
}
}
}
else
{
sprite_fetch_counter--;
if (sprite_fetch_counter == 0)
{
fetch_sprite = false;
}
}
}
}
public override void WriteReg(int addr, byte value)
{
switch (addr)
{
case 0xFF40: // LCDC
if (LCDC.Bit(7) && !value.Bit(7))
{
VRAM_access_read = true;
VRAM_access_write = true;
OAM_access_read = true;
OAM_access_write = true;
}
if (!LCDC.Bit(7) && value.Bit(7))
{
// don't draw for one frame after turning on
blank_frame = true;
}
LCDC = value;
break;
case 0xFF41: // STAT
// writing to STAT during mode 0 or 2 causes a STAT IRQ
if (LCDC.Bit(7))
{
if (((STAT & 3) == 0) || ((STAT & 3) == 1))
{
LYC_INT = true;
}
}
STAT = (byte)((value & 0xF8) | (STAT & 7) | 0x80);
break;
case 0xFF42: // SCY
scroll_y = value;
break;
case 0xFF43: // SCX
scroll_x = value;
// calculate the column number of the tile to start with
x_tile = (int)Math.Floor((float)(scroll_x) / 8);
break;
case 0xFF44: // LY
LY = 0; /*reset*/
break;
case 0xFF45: // LYC
LYC = value;
if (LCDC.Bit(7))
{
if (LY != LYC)
{
STAT &= 0xFB;
}
else
{
STAT |= 0x4;
}
}
break;
case 0xFF46: // DMA
DMA_addr = value;
DMA_start = true;
DMA_OAM_access = true;
DMA_clock = 0;
DMA_inc = 0;
break;
case 0xFF47: // BGP
BGP = value;
break;
case 0xFF48: // OBP0
obj_pal_0 = value;
break;
case 0xFF49: // OBP1
obj_pal_1 = value;
break;
case 0xFF4A: // WY
window_y = value;
break;
case 0xFF4B: // WX
window_x = value;
break;
}
}
public override void tick()
{
// the ppu only does anything if it is turned on via bit 7 of LCDC
if (LCDC.Bit(7))
{
// start the next scanline
if (cycle == 456)
{
// scanline callback
if ((LY + LY_inc) == Core._scanlineCallbackLine)
{
if (Core._scanlineCallback != null)
{
Core.GetGPU();
Core._scanlineCallback(LCDC);
}
}
cycle = 0;
LY += LY_inc;
Core.cpu.LY = LY;
no_scan = false;
if (LY == 0 && LY_inc == 0)
{
LY_inc = 1;
Core.in_vblank = false;
VBL_INT = false;
if (STAT.Bit(3))
{
HBL_INT = true;
}
STAT &= 0xFC;
// special note here, the y coordiate of the window is kept if the window is deactivated
// meaning it will pick up where it left off if re-enabled later
// so we don't reset it in the scanline loop
window_y_tile = 0;
window_y_tile_inc = 0;
window_started = false;
if (!LCDC.Bit(5))
{
window_is_reset = true;
}
}
// Automatically restore access to VRAM at this time (force end drawing)
// Who Framed Roger Rabbit seems to run into this.
VRAM_access_write = true;
VRAM_access_read = true;
if (LY == 144)
{
Core.in_vblank = true;
}
}
// exit vblank if LCD went from off to on
if (LCD_was_off)
{
//VBL_INT = false;
Core.in_vblank = false;
LCD_was_off = false;
// we exit vblank into mode 0 for 4 cycles
// but no hblank interrupt, presumably this only happens transitioning from mode 3 to 0
STAT &= 0xFC;
// also the LCD doesn't turn on right away
// also, the LCD does not enter mode 2 on scanline 0 when first turned on
no_scan = true;
cycle = 8;
}
// the VBL stat is continuously asserted
if ((LY >= 144))
{
if (STAT.Bit(4))
{
if ((cycle >= 4) && (LY == 144))
{
VBL_INT = true;
}
else if (LY > 144)
{
VBL_INT = true;
}
}
if ((cycle == 4) && (LY == 144))
{
HBL_INT = false;
// set STAT mode to 1 (VBlank) and interrupt flag if it is enabled
STAT &= 0xFC;
STAT |= 0x01;
if (Core.REG_FFFF.Bit(0))
{
Core.cpu.FlagI = true;
}
Core.REG_FF0F |= 0x01;
}
if ((LY >= 144) && (cycle == 4))
{
// a special case of OAM mode 2 IRQ assertion, even though PPU Mode still is 1
if (STAT.Bit(5))
{
OAM_INT = true;
}
}
if ((LY == 153) && (cycle == 6))
{
LY = 0;
LY_inc = 0;
Core.cpu.LY = LY;
}
}
if (!Core.in_vblank)
{
if (no_scan)
{
// timings are slightly different if we just turned on the LCD
// there is no mode 2 (presumably it missed the trigger)
// mode 3 is very short, probably in some self test mode before turning on?
if (cycle == 8)
{
if (LY != LYC)
{
LYC_INT = false;
STAT &= 0xFB;
}
if ((LY == LYC) && !STAT.Bit(2))
{
// set STAT coincidence FLAG and interrupt flag if it is enabled
STAT |= 0x04;
if (STAT.Bit(6))
{
LYC_INT = true;
}
}
}
if (cycle == 84)
{
STAT &= 0xFC;
STAT |= 0x03;
OAM_INT = false;
OAM_access_read = false;
OAM_access_write = false;
VRAM_access_read = false;
VRAM_access_write = false;
}
if (cycle == 256)
{
STAT &= 0xFC;
OAM_INT = false;
if (STAT.Bit(3))
{
HBL_INT = true;
}
OAM_access_read = true;
OAM_access_write = true;
VRAM_access_read = true;
VRAM_access_write = true;
}
}
else
{
if (cycle < 80)
{
if (cycle == 2)
{
if (LY != 0)
{
if (STAT.Bit(5))
{
OAM_INT = true;
}
}
}
else if (cycle == 4)
{
// apparently, writes can make it to OAM one cycle longer then reads
OAM_access_write = false;
// here mode 2 will be set to true and interrupts fired if enabled
STAT &= 0xFC;
STAT |= 0x2;
if (LY == 0)
{
if (STAT.Bit(5))
{
OAM_INT = true;
}
}
HBL_INT = false;
}
// here OAM scanning is performed
OAM_scan(cycle);
}
else if ((cycle >= 80) && (LY < 144))
{
if (cycle == 84)
{
STAT &= 0xFC;
STAT |= 0x03;
OAM_INT = false;
OAM_access_write = false;
VRAM_access_write = false;
}
// render the screen and handle hblank
render(cycle - 80);
}
}
}
if ((LY_inc == 0))
{
if (cycle == 12)
{
LYC_INT = false;
STAT &= 0xFB;
// Special case of LY = LYC
if ((LY == LYC) && !STAT.Bit(2))
{
// set STAT coincidence FLAG and interrupt flag if it is enabled
STAT |= 0x04;
if (STAT.Bit(6))
{
LYC_INT = true;
}
}
// also a special case of OAM mode 2 IRQ assertion, even though PPU Mode still is 1
if (STAT.Bit(5))
{
OAM_INT = true;
}
}
if (cycle == 92)
{
OAM_INT = false;
}
}
// here LY=LYC will be asserted or cleared (but only if LY isnt 0 as that's a special case)
if ((cycle == 2) && (LY != 0))
{
if (LY_inc == 1)
{
LYC_INT = false;
STAT &= 0xFB;
}
}
else if ((cycle == 4) && (LY != 0))
{
if ((LY == LYC) && !STAT.Bit(2))
{
// set STAT coincidence FLAG and interrupt flag if it is enabled
STAT |= 0x04;
if (STAT.Bit(6))
{
LYC_INT = true;
}
}
}
cycle++;
}
else
{
STAT &= 0xFC;
VBL_INT = LYC_INT = HBL_INT = OAM_INT = false;
Core.in_vblank = true;
LCD_was_off = true;
LY = 0;
Core.cpu.LY = LY;
cycle = 0;
}
// assert the STAT IRQ line if the line went from zero to 1
stat_line = VBL_INT | LYC_INT | HBL_INT | OAM_INT;
if (stat_line && !stat_line_old)
{
if (Core.REG_FFFF.Bit(1))
{
Core.cpu.FlagI = true;
}
Core.REG_FF0F |= 0x02;
}
stat_line_old = stat_line;
// process latch delays
//latch_delay();
}
public override void OAM_scan(int OAM_cycle)
{
// we are now in STAT mode 2
// TODO: maybe stat mode 2 flags are set at cycle 0 on visible scanlines?
if (OAM_cycle == 0)
{
OAM_access_read = false;
OAM_scan_index = 0;
SL_sprites_index = 0;
write_sprite = 0;
}
// the gameboy has 80 cycles to scan through 40 sprites, picking out the first 10 it finds to draw
// the following is a guessed at implmenentation based on how NES does it, it's probably pretty close
if (OAM_cycle < 10)
{
// start by clearing the sprite table (probably just clears X on hardware, but let's be safe here.)
SL_sprites[OAM_cycle * 4] = 0;
SL_sprites[OAM_cycle * 4 + 1] = 0;
SL_sprites[OAM_cycle * 4 + 2] = 0;
SL_sprites[OAM_cycle * 4 + 3] = 0;
}
else
{
if (write_sprite == 0)
{
if (OAM_scan_index < 40)
{
ushort temp = DMA_OAM_access ? Core.OAM[OAM_scan_index * 4] : (ushort)0xFF;
// (sprite Y - 16) equals LY, we have a sprite
if ((temp - 16) <= LY &&
((temp - 16) + 8 + (LCDC.Bit(2) ? 8 : 0)) > LY)
{
// always pick the first 10 in range sprites
if (SL_sprites_index < 10)
{
SL_sprites[SL_sprites_index * 4] = temp;
write_sprite = 1;
}
else
{
// if we already have 10 sprites, there's nothing to do, increment the index
OAM_scan_index++;
}
}
else
{
OAM_scan_index++;
}
}
}
else
{
ushort temp2 = DMA_OAM_access ? Core.OAM[OAM_scan_index * 4 + write_sprite] : (ushort)0xFF;
SL_sprites[SL_sprites_index * 4 + write_sprite] = temp2;
write_sprite++;
if (write_sprite == 4)
{
write_sprite = 0;
SL_sprites_index++;
OAM_scan_index++;
}
}
}
}
public override void WriteReg(int addr, byte value)
{
switch (addr)
{
case 0xFF40: // LCDC
if (LCDC.Bit(7) && !value.Bit(7))
{
VRAM_access_read = true;
VRAM_access_write = true;
OAM_access_read = true;
OAM_access_write = true;
clear_screen = true;
}
if (!LCDC.Bit(7) && value.Bit(7))
{
// don't draw for one frame after turning on
blank_frame = true;
}
LCDC = value;
break;
case 0xFF41: // STAT
// writing to STAT during mode 0 or 1 causes a STAT IRQ
// this appears to be a glitchy LYC compare
if (LCDC.Bit(7))
{
if (((STAT & 3) == 0) || ((STAT & 3) == 1))
{
LYC_INT = true;
//if (Core.REG_FFFF.Bit(1)) { Core.cpu.FlagI = true; }
//Core.REG_FF0F |= 0x02;
}
else
{
if (value.Bit(6))
{
if (LY == LYC)
{
LYC_INT = true;
}
else
{
LYC_INT = false;
}
}
}
}
STAT = (byte)((value & 0xF8) | (STAT & 7) | 0x80);
//if (!STAT.Bit(6)) { LYC_INT = false; }
if (!STAT.Bit(4))
{
VBL_INT = false;
}
break;
case 0xFF42: // SCY
scroll_y = value;
break;
case 0xFF43: // SCX
scroll_x = value;
break;
case 0xFF44: // LY
LY = 0; /*reset*/
break;
case 0xFF45: // LYC
LYC = value;
if (LCDC.Bit(7))
{
if (LY != LYC)
{
STAT &= 0xFB; LYC_INT = false;
}
else
{
STAT |= 0x4; LYC_INT = true;
}
// special case: the transition from 153 -> 0 acts strange
// the comparison to 153 expects to be true for longer then the value of LY expects to be 153
// this appears to be fixed in CGB
if ((LY_inc == 0) && cycle == 8)
{
if (153 != LYC)
{
STAT &= 0xFB; LYC_INT = false;
}
else
{
STAT |= 0x4; LYC_INT = true;
}
}
}
break;
case 0xFF46: // DMA
DMA_addr = value;
DMA_start = true;
DMA_OAM_access = true;
DMA_clock = 0;
DMA_inc = 0;
break;
case 0xFF47: // BGP
BGP = value;
break;
case 0xFF48: // OBP0
obj_pal_0 = value;
break;
case 0xFF49: // OBP1
obj_pal_1 = value;
break;
case 0xFF4A: // WY
window_y = value;
break;
case 0xFF4B: // WX
window_x = value;
break;
}
}
