Class: Amaterasu::GameBoy::Vram

Inherits:
Ram
  • Object
show all
Defined in:
lib/amaterasu/game_boy/vram.rb,
lib/amaterasu/game_boy/vram/tile.rb,
lib/amaterasu/game_boy/vram/tile_map.rb,
lib/amaterasu/game_boy/vram/tile_data.rb

Overview

Models the VRAM (Video RAM) from the DMG Game Boy.

The VRAM address range can be divided into 2 main parts.

  1. Tile Data:

- Lives in 0x8000 -> 0x97FF (6144 bytes)
- Each tile is composed of 8 x 8 = 64 pixels
- Each pixel is encoded as 2 bits in the DMG Game Boy
- So each tile has 64 * 2 = 128 bits (16 bytes)

  1. Tile Maps:

- Has a total of 2 Tile Maps (0x9800 -> 0x9BFF) / (0x9C00 -> 0x9FFF)
- Each Tile Map is a 32 x 32 grid of Tile indices (each index is 1 byte)
- So each Tile Map has exactly 1024 bytes (1 KiB)

Defined Under Namespace

Classes: Tile, TileData, TileMap

Constant Summary collapse

START_ADDRESS =

VRAM Start Address in the Memory Map

0x8000
END_ADDRESS =

VRAM End Address in the Memory Map

0x9FFF
SIZE_IN_BYTES =

VRAM Size in bytes: 8192 bytes (8 KiB)

(END_ADDRESS - START_ADDRESS) + 1

Instance Attribute Summary collapse

Attributes inherited from Ram

#size

Instance Method Summary collapse

Methods inherited from Ram

#disk_size, #read_backup, #read_byte, #restore_data, #save_data, #wipe_backup, #wipe_data, #write_byte

Constructor Details

#initialize ⇒ Vram

Creates “lens objects” passing the original VRAM @data Array, when a value is written into VRAM it will be correctly read by all the Tile Data and Tile Maps.



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# File 'lib/amaterasu/game_boy/vram.rb', line 35

def initialize
  super(size: SIZE_IN_BYTES, offset: START_ADDRESS)

  @tile_data     = TileData.new(vram_data: @data)
  @tile_map_low  = TileMap.new(vram_data: @data, base_offset: 0x1800)
  @tile_map_high = TileMap.new(vram_data: @data, base_offset: 0x1C00)
end

Instance Attribute Details

#tile_data ⇒ Object (readonly)

Exposes the tile data and maps to the PPU



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# File 'lib/amaterasu/game_boy/vram.rb', line 28

def tile_data
  @tile_data
end

#tile_map_high ⇒ Object (readonly)

Exposes the tile data and maps to the PPU



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# File 'lib/amaterasu/game_boy/vram.rb', line 28

def tile_map_high
  @tile_map_high
end

#tile_map_low ⇒ Object (readonly)

Exposes the tile data and maps to the PPU



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# File 'lib/amaterasu/game_boy/vram.rb', line 28

def tile_map_low
  @tile_map_low
end

Instance Method Details

#inspect ⇒ Object 



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# File 'lib/amaterasu/game_boy/vram.rb', line 43

def inspect
  '#<Vram ' \
    "@tile_data=#{@tile_data} " \
    "@tile_map_low=#{@tile_map_low} " \
    "@tile_map_high=#{@tile_map_high}>"
end