l65/samples/vcs_flush.l65

require'vcs'
mappers['4K']()

local HEADER_LEN = 92
local PICTURE_LEN = 64
local STEP_COUNT = 32

-- FLUSH text as playfield
local logo_img = assert(l65.image("flush.png")) -- analyse the image twice, so load it separately
@@logo_col samepage byte(0x00, 0xd4, 0x72, linecol(logo_img)) end
local pfs = playfield(logo_img)
for i=1,#pfs do
    local pf = pfs[i]
    section("logo_pf"..(i-1)) samepage byte(0, pf[1], pf[#pf], pf) end
end
local LOGO_HEIGHT = #pfs[1]

-- background
local bg = linecol("flushbg.png")
@@logo_bg_all
samepage
    @logo_bg_pre for i=1,8 do dc.b bg[1] end
    @logo_bg
        for i=1,13 do dc.b bg[1] end
        byte(bg)
        for i=1,13 do dc.b bg[#bg] end
    @logo_bg_post for i=1,8 do dc.b bg[#bg] end
end

-- generate offset tables into logo_pf*
do
    local DISP_HEIGHT = PICTURE_LEN
    local transfo,bgshift = {},{}
    for x=0,STEP_COUNT-1 do
        local theta = x/(STEP_COUNT-1) * math.pi/2 - math.pi/4
        local s,c = math.sin(theta),math.cos(theta)
        local ra,rb,rc,rd = -c, s-c, s+c, c
        for y=0,DISP_HEIGHT-1 do
            local r = DISP_HEIGHT / LOGO_HEIGHT
            local yn = r * (2 * y/(DISP_HEIGHT-1) - 1)
            local function f()
                local y = (s-yn) / c
                return math.min(math.floor((y+1)/2*LOGO_HEIGHT), LOGO_HEIGHT-1) + 3
            end
            local v
            if rd < rc then v = yn>rc and 0 or yn>rb and f(yn) or yn>ra and 2 or 0
            else v = yn>rd and 0 or yn>rc and 1 or yn>rb and f(yn) or 0 end
            transfo[x*DISP_HEIGHT+DISP_HEIGHT-y] = v
        end
        bgshift[#bgshift+1] = math.floor(math.sin(math.pi+theta)*LOGO_HEIGHT/4)
    end
    @@logo_transfo byte(transfo)
    @@logo_bgshift byte(bgshift)
end

-- rotation anim
do
    local PERIOD = 128
    local f = \x((math.sin(x*2*math.pi/PERIOD)+1)/2 * (STEP_COUNT-1))
    local rotation = {}
    for x=1,PERIOD do
        rotation[#rotation+1] = math.floor(math.min(f(x-1), (STEP_COUNT-1)))
    end
    @@logo_rotation byte(rotation)
end

local bg_ptr = 0x80
local trans_ptr = 0x82
local time = 0x84
local tmp = 0x85

local on_vblank = function()
    inc time asl time lsr time
    ldy time lda logo_rotation,y sta tmp

    ldy tmp lda logo_bgshift,y sta bg_ptr
    lda#logo_bg&0xff clc adc bg_ptr sta bg_ptr lda#logo_bg>>8 sta bg_ptr+1

    setptr(logo_transfo, trans_ptr)
    lda tmp asl asl asl asl asl asl clc adc trans_ptr sta trans_ptr
    lda trans_ptr+1 adc#0 sta trans_ptr+1
    lda tmp lsr lsr clc adc trans_ptr+1 sta trans_ptr+1

    ldy#PICTURE_LEN-1 lda (bg_ptr),y sta COLUBK
end

local kernel = function()
    ldy#HEADER_LEN @_header sta WSYNC dey bne _header
    samepage @_line
        lda (trans_ptr),y tax
        lda (bg_ptr),y 
        sta WSYNC sta COLUBK
        lda logo_col,x sta COLUPF
        lda logo_pf0,x sta PF0
        lda logo_pf1,x sta PF1
        lda logo_pf2,x sta PF2
        lda logo_pf3,x sta PF0
        lda logo_pf4,x sta PF1
        lda logo_pf5,x sta PF2
        iny cpy#PICTURE_LEN bne _line
    end
    lda#0 sta WSYNC sta PF0 sta PF1 sta PF2
end

@@main
    init()
@_frame
    overscan() vblank(on_vblank) screen(kernel) jmp _frame

;
writebin(filename..'.bin')
writesym(filename..'.sym')
print(stats)