NES Star Soldier (J) tile display for FCEUX

StarSoldier-tile.lua

----------------------------------------------------------------------
-- NES Star Soldier (J) tile display for FCEUX
----------------------------------------------------------------------


----------------------------------------------------------------------
-- util
----------------------------------------------------------------------

local function mem_read_u8(addr)
    return memory.readbyte(addr)
end

local function mem_read_bytes(addr, len)
    local buf = {}
    for i = 1, len do
        buf[i] = mem_read_u8(addr + i-1)
    end
    return buf
end


----------------------------------------------------------------------
-- main
----------------------------------------------------------------------

local COLS = 20
local ROWS = 15

local COLOR_GRID = "#00FFFF"

local fmt = string.format

local function get_info()
    local info = {}

    info.scroll_x = mem_read_u8(0x13)
    info.scroll_y = mem_read_u8(0x14)

    info.tiles = mem_read_bytes(0x06CA, COLS * ROWS)

    return info
end

local function line(src_x, src_y, dst_x, dst_y, color)
    gui.line(src_x, src_y, dst_x, dst_y, color)
end

local function text(x, y, str)
    gui.text(x, y, str)
end

local function draw_grid(scroll_x, scroll_y)
    local off_x = -scroll_x
    local off_y = -(scroll_y % 16) - 1

    for row = 0, ROWS-1 do
        line(          off_x, 16*row + off_y,
             16*COLS + off_x, 16*row + off_y,
             COLOR_GRID)
    end

    for col = 0, COLS-1 do
        line(16*col + off_x,           off_y,
             16*col + off_x, 16*ROWS + off_y,
             COLOR_GRID)
    end
end

local function draw_tile(tiles, scroll_x, scroll_y)
    local off_x = -scroll_x
    local off_y = -(scroll_y % 16) - 1

    for row = 0, ROWS-1 do
        for col = 0, COLS-1 do
            local tile = tiles[COLS*row + col + 1]
            text(16*col + off_x + 2, 16*row + off_y + 2,
                 fmt("%02X", tile))
        end
    end
end

local function draw()
    local info = get_info()

    draw_grid(info.scroll_x, info.scroll_y)

    draw_tile(info.tiles, info.scroll_x, info.scroll_y)
end

local function main()
    gui.opacity(0.7)

    emu.registerafter(draw)
end

main()