Fast vertex setting in Love using ImageData and the FFI

main.lua

local num_verts = 100000
local vertices = {}
for i=1,num_verts do
  vertices[i] = {0, 0, 0, 0, 255, 255, 255, 255}
end

local ffi = require('ffi')
ffi.cdef[[
typedef struct {
  float x, y;
  float s, t;
  unsigned char r, g, b, a;
} fm_vertex;
]]
local vertex_size = ffi.sizeof('fm_vertex')
local pixel_size = ffi.sizeof('unsigned char[4]')
local imageData = love.image.newImageData(num_verts / pixel_size * vertex_size, 1)
local data = ffi.cast("fm_vertex*", imageData:getPointer())

local times = {}

local mesh = love.graphics.newMesh(num_verts, 'fan', 'stream')

function love.load()
  for i=0,num_verts-1 do
    local vertex = data[i]
    vertex.r = 255
    vertex.g = 255
    vertex.b = 255
    vertex.a = 255
  end
end

local t = 0
function love.update(dt)
  t = t + dt
  local radius = 300
  for i=1,num_verts do
    local phi = (i - 1) / num_verts * math.pi * 2
    vertices[i][1] = math.cos(phi) * radius + math.cos(t + phi) * radius / 4
    vertices[i][2] = math.sin(phi) * radius

    local vertex = data[i - 1]
    vertex.x = vertices[i][1]
    vertex.y = vertices[i][2]
  end

  local start = love.timer.getTime()
  -- mesh:setVertices(vertices) -- SLOW
  mesh:setVertices(imageData) -- FAST
  local stop = love.timer.getTime()
  local time = stop - start
  table.insert(times, time)
end

function love.draw()
  love.graphics.draw(mesh, love.graphics.getWidth() / 2, love.graphics.getHeight() / 2)
end

function love.keypressed()
  local total = 0
  for i,time in ipairs(times) do
    total = total + time
  end
  print('average', string.format("%0.32f", total / #times))
end