SNES Lag Visualization

-- PARAMETERS

local END_OF_VBLANK = 0x2C3
local END_OF_GAME_LOOP = 0x75
-- location in ROM space, e.g. $0082C3 = 0x2C3

-------------

local V_TOP = 1
local V_BOTTOM = 38
local H_LEFT = 22
local H_RIGHT = 62

local vv, vh = -20, -30
local gv, gh = -20, -30
local lag = 0
local function get_vblank_scan()
    lag = lag + 1
    vh = memory.getregister("hcounter")
    vv = memory.getregister("vcounter")
end
memory.registerexec("ROM",END_OF_VBLANK,get_vblank_scan)
local function get_game_scan()
    lag = 0
    gv = memory.getregister("vcounter")
    gh = memory.getregister("hcounter")
end
memory.registerexec("ROM",END_OF_GAME_LOOP,get_game_scan)

function on_paint()
    gui.top_gap(2*V_TOP)
    gui.left_gap(2*H_LEFT)
    gui.right_gap(2*H_RIGHT)
    gui.bottom_gap(2*V_BOTTOM)

    if lag ~= 0 then
        gui.rectangle(2*(0-H_LEFT),2*(0-V_TOP),2*340,2*263,0x6000FF00,0x6000FF00)
    else
        if gv < 0xE1 then
            gui.rectangle(2*(0-H_LEFT),2*(0xE1-V_TOP),2*340,2*38,0x6000FF00,0x6000FF00)
            gui.rectangle(2*(0-H_LEFT),2*(0-V_TOP),2*340,2*gv,0x6000FF00,0x6000FF00)
            gui.rectangle(2*(0-H_LEFT),2*(gv-V_TOP),2*(math.floor(gh/4)),2*1,0x6000FF00,0x6000FF00)
        else
            gui.rectangle(2*(0-H_LEFT),2*(0xE1-V_TOP),2*340,2*(gv-0xE1),0x6000FF00,0x6000FF00)
            gui.rectangle(2*(0-H_LEFT),2*(gv-V_TOP),2*(math.floor(gh/4)),2*1,0x6000FF00,0x6000FF00)
        end
    end

    if vv < 0xE1 then
        gui.rectangle(2*(0-H_LEFT),2*(0xE1-V_TOP),2*340,2*38,0x60FF0000,0x60FF0000)
        gui.rectangle(2*(0-H_LEFT),2*(0-V_TOP),2*340,2*vv,0x60FF0000,0x60FF0000)
        gui.rectangle(2*(0-H_LEFT),2*(vv-V_TOP),2*(math.floor(vh/4)),2*1,0x60FF0000,0x60FF0000)
    else
        gui.rectangle(2*(0-H_LEFT),2*(0xE1-V_TOP),2*340,2*(vv-0xE1),0x60FF0000,0x60FF0000)
        gui.rectangle(2*(0-H_LEFT),2*(vv-V_TOP),2*(math.floor(vh/4)),2*1,0x60FF0000,0x60FF0000)
    end

    gui.text(10,10,"lag: " .. lag)
    gui.text(10,30,"game: (" .. gv .. "," .. gh .. ")")
    gui.text(10,50,"vblank: (" .. vv .. "," .. vh .. ")")
end
gui.repaint()