-- ROTOZOOMER TUTORIAL: IEScript submission of the Mode7 blitter.
--
-- This program stages a 256 by 256 texture in guest memory, renders it into
-- a 640 by 480 back buffer, then copies that buffer to the framebuffer. The
-- common affine mapping is evaluated by the blitter, not by this Lua loop:
--
--   U = U0 + x * dU_col + y * dU_row
--   V = V0 + x * dV_col + y * dV_row
--
-- U0 and V0 are signed 16.16 values. `fixed` converts a Lua number to that
-- representation. The four deltas form the rotation and scale matrix. The
-- texture-width and texture-height registers receive 255, the wrap masks for
-- this power-of-two texture, rather than the dimensions themselves.
--
-- `stage_assets` is host-side setup. It pauses the guest CPU while writing
-- file contents into guest memory. `render_frame` is the guest-facing part:
-- it writes the documented blitter registers, starts an operation, and polls
-- BLT_CTRL until the busy bit clears before reusing the registers or buffer.
--
-- The copy operation makes the Mode7 destination a private back buffer. It
-- does not make presentation atomic. `sys.wait_frames(1)` yields once after a
-- completed copy. Set IE_ROTO_DISABLE_AUDIO to skip the optional MIDI setup,
-- or IE_ROTO_MAX_FRAMES to stop after a chosen number of completed frames.

local VIDEO_CTRL = 0xF0000
local VIDEO_MODE = 0xF0004
local BLT_CTRL = 0xF001C
local BLT_OP = 0xF0020
local BLT_SRC = 0xF0024
local BLT_DST = 0xF0028
local BLT_WIDTH = 0xF002C
local BLT_HEIGHT = 0xF0030
local BLT_SRC_STRIDE = 0xF0034
local BLT_DST_STRIDE = 0xF0038
local BLT_MODE7_U0 = 0xF0058
local BLT_MODE7_V0 = 0xF005C
local BLT_MODE7_DU_COL = 0xF0060
local BLT_MODE7_DV_COL = 0xF0064
local BLT_MODE7_DU_ROW = 0xF0068
local BLT_MODE7_DV_ROW = 0xF006C
local BLT_MODE7_TEX_W = 0xF0070
local BLT_MODE7_TEX_H = 0xF0074
local VIDEO_COLOR_MODE = 0xF0080
local VIDEO_FB_BASE = 0xF0084
local BLT_FLAGS = 0xF0488

local MIDI_PLAY_PTR = 0xF0BA0
local MIDI_PLAY_LEN = 0xF0BA4
local MIDI_PLAY_CTRL = 0xF0BA8
local MIDI_VOLUME = 0xF0BB4

local MODE_640x480 = 0
local BLT_START = 1
local BLT_BUSY = 2
local BLT_OP_COPY = 0
local BLT_OP_MODE7 = 5

local WIDTH = 640
local HEIGHT = 480
local BYTES_PER_PIXEL = 4
local TEXTURE_WIDTH = 256
local TEXTURE_HEIGHT = 256
local TEXTURE_BASE = 0x600000
local VRAM_BASE = 0x100000
local BACK_BUFFER = 0x900000
local MIDI_DATA_BASE = 0xA40000
local FRAME_BYTES = WIDTH * HEIGHT * BYTES_PER_PIXEL
local FRAME_STRIDE = WIDTH * BYTES_PER_PIXEL
local TEXTURE_STRIDE = TEXTURE_WIDTH * BYTES_PER_PIXEL

local audio_started = false

local function write32(addr, value)
    mem.write32(addr, value)
end

local function fixed(n)
    if n >= 0 then
        return math.floor(n * 65536 + 0.5)
    end
    return math.floor(n * 65536 - 0.5)
end

local function blit_wait()
    while bit32.band(mem.read32(BLT_CTRL), BLT_BUSY) ~= 0 do
        sys.wait_ms(1)
    end
end

local function stop_midi()
    if audio_started then
        write32(MIDI_PLAY_CTRL, 2)
        audio_started = false
    end
end

local function stage_assets()
    local texture = sys.read_file("sdk/examples/assets/rotozoomtexture_ies.raw")
    cpu.freeze()
    mem.write_block(TEXTURE_BASE, texture)
    cpu.resume()

    if IE_ROTO_DISABLE_AUDIO then
        return
    end

    local midi = sys.read_file("sdk/examples/assets/music/yourlove.mid")
    cpu.freeze()
    mem.write_block(MIDI_DATA_BASE, midi)
    cpu.resume()

    write32(MIDI_PLAY_PTR, MIDI_DATA_BASE)
    write32(MIDI_PLAY_LEN, string.len(midi))
    write32(MIDI_VOLUME, 180)
    write32(MIDI_PLAY_CTRL, 1 + 4)
    audio_started = true
end

local function configure_video()
    video.write_reg(VIDEO_MODE, MODE_640x480)
    video.write_reg(VIDEO_COLOR_MODE, 0)
    video.write_reg(VIDEO_FB_BASE, 0)
    video.write_reg(BLT_FLAGS, 0)
    video.write_reg(VIDEO_CTRL, 1)
end

local function render_frame(angle, scale_phase)
    local zoom = 0.85 + math.sin(scale_phase) * 0.35
    local ca = math.cos(angle) * zoom
    local sa = math.sin(angle) * zoom

    local du_col = fixed(ca)
    local dv_col = fixed(sa)
    local du_row = fixed(-sa)
    local dv_row = fixed(ca)
    local u0 = fixed(TEXTURE_WIDTH / 2) - (WIDTH / 2) * du_col - (HEIGHT / 2) * du_row
    local v0 = fixed(TEXTURE_HEIGHT / 2) - (WIDTH / 2) * dv_col - (HEIGHT / 2) * dv_row

    write32(BLT_OP, BLT_OP_MODE7)
    write32(BLT_SRC, TEXTURE_BASE)
    write32(BLT_DST, BACK_BUFFER)
    write32(BLT_WIDTH, WIDTH)
    write32(BLT_HEIGHT, HEIGHT)
    write32(BLT_SRC_STRIDE, TEXTURE_STRIDE)
    write32(BLT_DST_STRIDE, FRAME_STRIDE)
    write32(BLT_MODE7_U0, u0)
    write32(BLT_MODE7_V0, v0)
    write32(BLT_MODE7_DU_COL, du_col)
    write32(BLT_MODE7_DV_COL, dv_col)
    write32(BLT_MODE7_DU_ROW, du_row)
    write32(BLT_MODE7_DV_ROW, dv_row)
    write32(BLT_MODE7_TEX_W, TEXTURE_WIDTH - 1)
    write32(BLT_MODE7_TEX_H, TEXTURE_HEIGHT - 1)
    write32(BLT_CTRL, BLT_START)
    blit_wait()

    write32(BLT_OP, BLT_OP_COPY)
    write32(BLT_SRC, BACK_BUFFER)
    write32(BLT_DST, VRAM_BASE)
    write32(BLT_WIDTH, WIDTH)
    write32(BLT_HEIGHT, HEIGHT)
    write32(BLT_SRC_STRIDE, FRAME_STRIDE)
    write32(BLT_DST_STRIDE, FRAME_STRIDE)
    write32(BLT_CTRL, BLT_START)
    blit_wait()
end

local function main()
    stage_assets()
    configure_video()

    local angle = 0
    local scale_phase = 0
    local frame = 0
    while true do
        angle = angle + 0.03
        scale_phase = scale_phase + 0.01
        render_frame(angle, scale_phase)
        frame = frame + 1
        if IE_ROTO_MAX_FRAMES and frame >= IE_ROTO_MAX_FRAMES then
            break
        end
        sys.wait_frames(1)
    end
    stop_midi()
end

local ok, err = pcall(main)
stop_midi()
if not ok then
    error(err)
end