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FIx the bug with the missing vertical object lines
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The bug would ocour only for objects drawn with odd scx register.
Since the state machine of the sprite fetcher worked in steps
of 2 t_cycles it would miss some lines.
Moved the state machine to work for every t_cycle and not
for the even ones.
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@alloncm
alloncm committed Sep 3, 2021
1 parent 1926087 commit dff63cb
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Showing 3 changed files with 86 additions and 63 deletions.
13 changes: 12 additions & 1 deletion lib_gb/src/ppu/fifo/bg_fetcher.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ pub struct BGFetcher{
rendered_window:bool,
rendering_window:bool,
current_fetching_state:FethcingState,
t_cycles_counter:u8,
}

impl BGFetcher{
Expand All @@ -20,7 +21,8 @@ impl BGFetcher{
fifo:Vec::<u8>::with_capacity(8),
window_line_counter:0,
rendered_window:false,
rendering_window:false
rendering_window:false,
t_cycles_counter:0
}
}

Expand All @@ -30,10 +32,12 @@ impl BGFetcher{
self.current_fetching_state = FethcingState::TileNumber;
self.rendered_window = false;
self.rendering_window = false;
self.t_cycles_counter = 0;
}

pub fn pause(&mut self){
self.current_fetching_state = FethcingState::TileNumber;
self.t_cycles_counter = 0;
}

pub fn try_increment_window_counter(&mut self){
Expand All @@ -43,6 +47,11 @@ impl BGFetcher{
}

pub fn fetch_pixels(&mut self, vram:&VRam, lcd_control:u8, ly_register:u8, window_pos:&Vec2<u8>, bg_pos:&Vec2<u8>){
if self.t_cycles_counter % 2 == 0{
self.t_cycles_counter = (self.t_cycles_counter + 1) % 8;
return;
}

let last_rendering_status = self.rendering_window;
self.rendering_window = self.is_redering_wnd(lcd_control, window_pos, ly_register);
if self.rendering_window{
Expand Down Expand Up @@ -105,6 +114,8 @@ impl BGFetcher{
}
}
}

self.t_cycles_counter = (self.t_cycles_counter + 1) % 8;
}

fn get_tila_data_address(&self, lcd_control:u8, bg_pos:&Vec2<u8>, ly_register:u8, tile_num:u8)->u16{
Expand Down
48 changes: 24 additions & 24 deletions lib_gb/src/ppu/fifo/fifo_ppu.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -214,31 +214,31 @@ impl<GFX:GfxDevice> FifoPpu<GFX>{
self.t_cycles_passed += 2;
}
PpuState::PixelTransfer=>{
if self.pixel_x_pos < 160{
if self.lcd_control & BIT_1_MASK != 0{
self.sprite_fetcher.fetch_pixels(&self.vram, self.lcd_control, self.ly_register, self.pixel_x_pos);
}
if self.sprite_fetcher.rendering{
self.bg_fetcher.pause();
}
else{
self.bg_fetcher.fetch_pixels(&self.vram, self.lcd_control, self.ly_register, &self.window_pos, &self.bg_pos);
for _ in 0..2{
self.try_push_to_lcd();
if self.pixel_x_pos == 160 {
self.state = PpuState::Hblank;
if self.h_blank_interrupt_request{
self.trigger_stat_interrupt = true;
}
self.bg_fetcher.try_increment_window_counter();
self.bg_fetcher.reset();
self.sprite_fetcher.reset();
for _ in 0..2{
if self.pixel_x_pos < 160{
if self.lcd_control & BIT_1_MASK != 0{
self.sprite_fetcher.fetch_pixels(&self.vram, self.lcd_control, self.ly_register, self.pixel_x_pos);
}
if self.sprite_fetcher.rendering{
self.bg_fetcher.pause();
}
else{
self.bg_fetcher.fetch_pixels(&self.vram, self.lcd_control, self.ly_register, &self.window_pos, &self.bg_pos);
self.try_push_to_lcd();
if self.pixel_x_pos == 160 {
self.state = PpuState::Hblank;
if self.h_blank_interrupt_request{
self.trigger_stat_interrupt = true;
}
self.bg_fetcher.try_increment_window_counter();
self.bg_fetcher.reset();
self.sprite_fetcher.reset();

// If im on the first iteration and finished the 160 pixels break;
// In this case the number of t_cycles should be eneven but it will break
// my code way too much for now so Im leaving this as it is... (maybe in the future)
break;
}
// If im on the first iteration and finished the 160 pixels break;
// In this case the number of t_cycles should be eneven but it will break
// my code way too much for now so Im leaving this as it is... (maybe in the future)
break;
}
}
}
}
Expand Down
88 changes: 50 additions & 38 deletions lib_gb/src/ppu/fifo/sprite_fetcher.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@ pub struct SpriteFetcher{

current_fetching_state:FethcingState,
current_oam_entry:u8,
t_cycle_inner_state_counter:u8,
}

impl SpriteFetcher{
Expand All @@ -34,14 +35,16 @@ impl SpriteFetcher{
oam_entries_len:0,
oam_entries,
fifo:Vec::<(u8,u8)>::with_capacity(8),
rendering:false
rendering:false,
t_cycle_inner_state_counter:0,
}
}

pub fn reset(&mut self){
self.current_oam_entry = 0;
self.oam_entries_len = 0;
self.current_fetching_state = FethcingState::TileNumber;
self.t_cycle_inner_state_counter = 0;
self.fifo.clear();
self.rendering = false;
}
Expand All @@ -67,54 +70,63 @@ impl SpriteFetcher{
self.rendering = false;
}
FethcingState::LowTileData(tile_num)=>{
let oam_attribute = &self.oam_entries[self.current_oam_entry as usize];
let current_tile_data_address = Self::get_current_tile_data_address(ly_register, oam_attribute, sprite_size, tile_num);
let low_data = vram.read_current_bank(current_tile_data_address);
self.current_fetching_state = FethcingState::HighTileData(tile_num, low_data);
if self.t_cycle_inner_state_counter % 2 != 0{
let oam_attribute = &self.oam_entries[self.current_oam_entry as usize];
let current_tile_data_address = Self::get_current_tile_data_address(ly_register, oam_attribute, sprite_size, tile_num);
let low_data = vram.read_current_bank(current_tile_data_address);
self.current_fetching_state = FethcingState::HighTileData(tile_num, low_data);
}
}
FethcingState::HighTileData(tile_num, low_data)=>{
let oam_attribute = &self.oam_entries[self.current_oam_entry as usize];
let current_tile_data_address = Self::get_current_tile_data_address(ly_register, oam_attribute, sprite_size, tile_num);
let high_data = vram.read_current_bank(current_tile_data_address + 1);
self.current_fetching_state = FethcingState::Push(low_data, high_data);
if self.t_cycle_inner_state_counter % 2 != 0{
let oam_attribute = &self.oam_entries[self.current_oam_entry as usize];
let current_tile_data_address = Self::get_current_tile_data_address(ly_register, oam_attribute, sprite_size, tile_num);
let high_data = vram.read_current_bank(current_tile_data_address + 1);
self.current_fetching_state = FethcingState::Push(low_data, high_data);
}
}
FethcingState::Push(low_data, high_data)=>{
let oam_attribute = &self.oam_entries[self.current_oam_entry as usize];
let start_x = self.fifo.len();

let skip_x = 8 - (oam_attribute.x - current_x_pos) as usize;

if oam_attribute.flip_x{
for i in (0 + skip_x)..8{
let mask = 1 << i;
let mut pixel = (low_data & mask) >> i;
pixel |= ((high_data & mask) >> i) << 1;
if i + skip_x >= start_x {
self.fifo.push((pixel, self.current_oam_entry));
}
else if self.fifo[i + skip_x].0 == 0{
self.fifo[i+ skip_x] = (pixel, self.current_oam_entry);
if self.t_cycle_inner_state_counter % 2 != 0{

let oam_attribute = &self.oam_entries[self.current_oam_entry as usize];
let start_x = self.fifo.len();

let skip_x = 8 - (oam_attribute.x - current_x_pos) as usize;

if oam_attribute.flip_x{
for i in (0 + skip_x)..8{
let mask = 1 << i;
let mut pixel = (low_data & mask) >> i;
pixel |= ((high_data & mask) >> i) << 1;
if i + skip_x >= start_x {
self.fifo.push((pixel, self.current_oam_entry));
}
else if self.fifo[i + skip_x].0 == 0{
self.fifo[i+ skip_x] = (pixel, self.current_oam_entry);
}
}
}
}
else{
for i in (0..(8 - skip_x)).rev(){
let mask = 1 << i;
let mut pixel = (low_data & mask) >> i;
pixel |= ((high_data & mask) >> i) << 1;
if 7 - skip_x - i >= start_x {
self.fifo.push((pixel, self.current_oam_entry));
}
else if self.fifo[7 - skip_x - i].0 == 0{
self.fifo[7 - skip_x - i] = (pixel, self.current_oam_entry);
else{
for i in (0..(8 - skip_x)).rev(){
let mask = 1 << i;
let mut pixel = (low_data & mask) >> i;
pixel |= ((high_data & mask) >> i) << 1;
if 7 - skip_x - i >= start_x {
self.fifo.push((pixel, self.current_oam_entry));
}
else if self.fifo[7 - skip_x - i].0 == 0{
self.fifo[7 - skip_x - i] = (pixel, self.current_oam_entry);
}
}
}
}

self.current_fetching_state = FethcingState::TileNumber;
self.current_oam_entry += 1;
self.current_fetching_state = FethcingState::TileNumber;
self.current_oam_entry += 1;
}
}
}

self.t_cycle_inner_state_counter = (self.t_cycle_inner_state_counter + 1) % 8;
}

// Receiving the tile_num since in case of extended sprite this could change (the first bit is reset)
Expand Down

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