64x64 PICO-8 resolution with run-time zoom

-- interpolated value - [0.5, 1]
local zoom = 1
-- discrete value - either 0.5 or 1
local zoom_target = 1

function _update()
    -- write any game update logic here

    -- end game update logic

    if btnp(5) then
        zoom_target = zoom_target == 1 and 0.5 or 1
    end

    zoom = lerp(zoom, zoom_target, 0.2)
end

function lerp(from, to, amount)
    local dist = to - from
    if abs(dist) <= 0.01 then return to end
    return from + (dist * amount)
end

function _draw()
    -- set video mode to 128x128
    poke(0x5f2c, 0)

    -- do your game draw operations here as normal

    -- end game draw operations

    -- set video mode to 64x64
    poke(0x5f2c, 3)

    -- video remapping (screen is now treated as the spritesheet for draw operations)
    poke(0x5f54, 0x60)

    -- draw screen to screen
    -- (originx,originy) is the coordinate center of the zoom.
    -- (-32,-32) will put the center of the 128x128 canvas on the center of the 64x64 screen.
    local sx = originx * (zoom - 0.5) * 2
    local sy = originy * (zoom - 0.5) * 2
    local sw = 128 * zoom
    local sh = 128 * zoom
    -- treat the screen as a spritesheet when drawing to the screen (thanks video remapping)
    sspr(0, 0, 128, 128, sx, sy, sw, sh)

    -- video remap back to defaults (screen is the screen, spritesheet is the spritesheet)
    poke(0x5f54, 0x00)
end