Class: Rubyboy::Ppu

Inherits:
Object
  • Object
show all
Defined in:
lib/rubyboy/ppu.rb

Constant Summary collapse

MODE = 
{
  hblank: 0,
  vblank: 1,
  oam_scan: 2,
  drawing: 3
}.freeze
LCDC = 
{
  bg_window_enable: 0,
  sprite_enable: 1,
  sprite_size: 2,
  bg_tile_map_area: 3,
  bg_window_tile_data_area: 4,
  window_enable: 5,
  window_tile_map_area: 6,
  lcd_ppu_enable: 7
}.freeze
STAT = 
{
  ly_eq_lyc: 2,
  hblank: 3,
  vblank: 4,
  oam_scan: 5,
  lyc: 6
}.freeze
SPRITE_FLAGS = 
{
  bank: 3,
  dmg_palette: 4,
  x_flip: 5,
  y_flip: 6,
  priority: 7
}.freeze
LCD_WIDTH = 
160
LCD_HEIGHT = 
144
OAM_SCAN_CYCLES = 
80
DRAWING_CYCLES = 
172
HBLANK_CYCLES = 
204
ONE_LINE_CYCLES = 
OAM_SCAN_CYCLES + DRAWING_CYCLES + HBLANK_CYCLES

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(interrupt) ⇒ Ppu

Returns a new instance of Ppu.



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# File 'lib/rubyboy/ppu.rb', line 49

def initialize(interrupt)
  @mode = MODE[:oam_scan]
  @lcdc = 0x91
  @stat = 0x00
  @scy = 0x00
  @scx = 0x00
  @ly = 0x00
  @lyc = 0x00
  @obp0 = 0x00
  @obp1 = 0x00
  @wy = 0x00
  @wx = 0x00
  @bgp = 0x00
  @vram = Array.new(0x2000, 0x00)
  @oam = Array.new(0xa0, 0x00)
  @wly = 0x00
  @cycles = 0
  @interrupt = interrupt
  @buffer = Array.new(144 * 160 * 3, 0x00)
  @bg_pixels = Array.new(LCD_WIDTH, 0x00)
end

Instance Attribute Details

#buffer ⇒ Object (readonly)

Returns the value of attribute buffer.



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# File 'lib/rubyboy/ppu.rb', line 5

def buffer
  @buffer
end

Instance Method Details

#read_byte(addr) ⇒ Object 



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# File 'lib/rubyboy/ppu.rb', line 71

def read_byte(addr)
  case addr
  when 0x8000..0x9fff
    @mode == MODE[:drawing] ? 0xff : @vram[addr - 0x8000]
  when 0xfe00..0xfe9f
    @mode == MODE[:oam_scan] || @mode == MODE[:drawing] ? 0xff : @oam[addr - 0xfe00]
  when 0xff40
    @lcdc
  when 0xff41
    @stat | 0x80 | @mode
  when 0xff42
    @scy
  when 0xff43
    @scx
  when 0xff44
    @ly
  when 0xff45
    @lyc
  when 0xff47
    @bgp
  when 0xff48
    @obp0
  when 0xff49
    @obp1
  when 0xff4a
    @wy
  when 0xff4b
    @wx
  end
end

#render_bg ⇒ Object 



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# File 'lib/rubyboy/ppu.rb', line 189

def render_bg
  return if @lcdc[LCDC[:bg_window_enable]] == 0

  y = (@ly + @scy) % 256
  tile_map_addr = @lcdc[LCDC[:bg_tile_map_area]] == 0 ? 0x1800 : 0x1c00
  tile_map_addr += (y / 8) * 32
  LCD_WIDTH.times do |i|
    x = (i + @scx) % 256
    tile_index = get_tile_index(tile_map_addr + (x / 8))
    pixel = get_pixel(tile_index << 4, 7 - (x % 8), (y % 8) * 2)
    color = get_color(@bgp, pixel)
    base = @ly * LCD_WIDTH * 3 + i * 3
    @buffer[base] = color
    @buffer[base + 1] = color
    @buffer[base + 2] = color
    @bg_pixels[i] = pixel
  end
end

#render_sprites ⇒ Object 



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# File 'lib/rubyboy/ppu.rb', line 232

def render_sprites
  return if @lcdc[LCDC[:sprite_enable]] == 0

  sprite_height = @lcdc[LCDC[:sprite_size]] == 0 ? 8 : 16
  sprites = []
  cnt = 0

  @oam.each_slice(4) do |y, x, tile_index, flags|
    y = (y - 16) % 256
    x = (x - 8) % 256
    next if y > @ly || y + sprite_height <= @ly

    sprites << { y:, x:, tile_index:, flags: }
    cnt += 1
    break if cnt == 10
  end
  sprites = sprites.sort_by.with_index { |sprite, i| [-sprite[:x], -i] }

  sprites.each do |sprite|
    flags = sprite[:flags]
    pallet = flags[SPRITE_FLAGS[:dmg_palette]] == 0 ? @obp0 : @obp1
    tile_index = sprite[:tile_index]
    tile_index &= 0xfe if sprite_height == 16
    y = (@ly - sprite[:y]) % 256
    y = sprite_height - y - 1 if flags[SPRITE_FLAGS[:y_flip]] == 1
    tile_index = (tile_index + 1) % 256 if y >= 8
    y %= 8

    8.times do |x|
      x_flipped = flags[SPRITE_FLAGS[:x_flip]] == 1 ? 7 - x : x

      pixel = get_pixel(tile_index << 4, 7 - x_flipped, (y % 8) * 2)
      i = (sprite[:x] + x) % 256

      next if pixel == 0 || i >= LCD_WIDTH
      next if flags[SPRITE_FLAGS[:priority]] == 1 && @bg_pixels[i] != 0

      color = get_color(pallet, pixel)
      base = @ly * LCD_WIDTH * 3 + i * 3
      @buffer[base] = color
      @buffer[base + 1] = color
      @buffer[base + 2] = color
    end
  end
end

#render_window ⇒ Object 



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# File 'lib/rubyboy/ppu.rb', line 208

def render_window
  return if @lcdc[LCDC[:bg_window_enable]] == 0 || @lcdc[LCDC[:window_enable]] == 0 || @ly < @wy

  rendered = false
  y = @wly
  tile_map_addr = @lcdc[LCDC[:window_tile_map_area]] == 0 ? 0x1800 : 0x1c00
  tile_map_addr += (y / 8) * 32
  LCD_WIDTH.times do |i|
    next if i < @wx - 7

    rendered = true
    x = i - (@wx - 7)
    tile_index = get_tile_index(tile_map_addr + (x / 8))
    pixel = get_pixel(tile_index << 4, 7 - (x % 8), (y % 8) * 2)
    color = get_color(@bgp, pixel)
    base = @ly * LCD_WIDTH * 3 + i * 3
    @buffer[base] = color
    @buffer[base + 1] = color
    @buffer[base + 2] = color
    @bg_pixels[i] = pixel
  end
  @wly += 1 if rendered
end

#step(cycles) ⇒ Object 



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# File 'lib/rubyboy/ppu.rb', line 133

def step(cycles)
  return false if @lcdc[LCDC[:lcd_ppu_enable]] == 0

  res = false
  @cycles += cycles

  case @mode
  when MODE[:oam_scan]
    if @cycles >= OAM_SCAN_CYCLES
      @cycles -= OAM_SCAN_CYCLES
      @mode = MODE[:drawing]
    end
  when MODE[:drawing]
    if @cycles >= DRAWING_CYCLES
      render_bg
      render_window
      render_sprites
      @cycles -= DRAWING_CYCLES
      @mode = MODE[:hblank]
      @interrupt.request(:lcd) if @stat[STAT[:hblank]] == 1
    end
  when MODE[:hblank]
    if @cycles >= HBLANK_CYCLES
      @cycles -= HBLANK_CYCLES
      @ly += 1
      handle_ly_eq_lyc

      if @ly == LCD_HEIGHT
        @mode = MODE[:vblank]
        @interrupt.request(:vblank)
        @interrupt.request(:lcd) if @stat[STAT[:vblank]] == 1
      else
        @mode = MODE[:oam_scan]
        @interrupt.request(:lcd) if @stat[STAT[:oam_scan]] == 1
      end
    end
  when MODE[:vblank]
    if @cycles >= ONE_LINE_CYCLES
      @cycles -= ONE_LINE_CYCLES
      @ly += 1
      handle_ly_eq_lyc

      if @ly == 154
        @ly = 0
        @wly = 0
        handle_ly_eq_lyc
        @mode = MODE[:oam_scan]
        @interrupt.request(:lcd) if @stat[STAT[:oam_scan]] == 1
        res = true
      end
    end
  end

  res
end

#write_byte(addr, value) ⇒ Object 



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# File 'lib/rubyboy/ppu.rb', line 102

def write_byte(addr, value)
  case addr
  when 0x8000..0x9fff
    @vram[addr - 0x8000] = value if @mode != MODE[:drawing]
  when 0xfe00..0xfe9f
    @oam[addr - 0xfe00] = value if @mode != MODE[:oam_scan] && @mode != MODE[:drawing]
  when 0xff40
    @lcdc = value
  when 0xff41
    @stat = value & 0x78
  when 0xff42
    @scy = value
  when 0xff43
    @scx = value
  when 0xff44
    # ly is read only
  when 0xff45
    @lyc = value
  when 0xff47
    @bgp = value
  when 0xff48
    @obp0 = value
  when 0xff49
    @obp1 = value
  when 0xff4a
    @wy = value
  when 0xff4b
    @wx = value
  end
end