A testbed for light probe generation from a dynamically rendered skybox

lightprobe_skybox.lua

local skybox = {}        -- from https://github.com/jmiskovic/lovr-atmo
skybox.__index = skybox

function skybox.new(resolution)
  local self = setmetatable({}, skybox)
  self.resolution = math.floor(resolution or 256)
  assert(self.resolution > 0 and self.resolution < 6000)
  self.cubetex = lovr.graphics.newTexture(
    self.resolution, self.resolution, 6,
    {type='cube', mipmaps=false, usage = {'render', 'sample', 'transfer'}})
  self.horizon_color = lovr.math.newVec3()
  return self
end
function skybox:bake(drawfn)
  -- render scene to cubemap texture
  local render_pass = lovr.graphics.getPass('render', {self.cubetex, samples=1, mipmap=false})
  local projection = mat4():perspective(math.pi / 2, 1, 0, 0)
  local transforms = {
    mat4():lookAt(vec3(), vec3( 1, 0, 0), vec3(0, 1, 0)),
    mat4():lookAt(vec3(), vec3(-1, 0, 0), vec3(0, 1, 0)),
    mat4():lookAt(vec3(), vec3( 0, 1, 0), vec3(0, 0,-1)),
    mat4():lookAt(vec3(), vec3( 0,-1, 0), vec3(0, 0, 1)),
    mat4():lookAt(vec3(), vec3( 0, 0, 1), vec3(0, 1, 0)),
    mat4():lookAt(vec3(), vec3( 0, 0,-1), vec3(0, 1, 0))
  }
  for i, transform in ipairs(transforms) do
    render_pass:setProjection(i, projection)
    render_pass:setViewPose(i, transform)
  end
  drawfn(render_pass)
  -- read back the horizon color
  local transfer_pass = lovr.graphics.getPass('transfer')
  local readbacks = {
    transfer_pass:read(self.cubetex, 0, 0, 1, 1, self.resolution, self.resolution),
    transfer_pass:read(self.cubetex, 0, 0, 2, 1, self.resolution, self.resolution),
    transfer_pass:read(self.cubetex, 0, 0, 3, 1, self.resolution, self.resolution),
    transfer_pass:read(self.cubetex, 0, 0, 4, 1, self.resolution, self.resolution),
    transfer_pass:read(self.cubetex, 0, 0, 5, 1, self.resolution, self.resolution),
    transfer_pass:read(self.cubetex, 0, 0, 6, 1, self.resolution, self.resolution)
  }
  lovr.graphics.submit(render_pass, transfer_pass)
  self.images = {}
  for i, readback in ipairs(readbacks) do
    readback:wait()
    self.images[i] = readback:getImage()
    --lovr.filesystem.write('img'..i..'.png', self.images[i]:encode())
  end
end
function skybox:draw(pass)
  pass:setColor(1,1,1)
  pass:skybox(self.cubetex)
end
--------------------------------------

local box = skybox.new(64)

probeShader = lovr.graphics.newShader('unlit', [[
  layout(set = 2, binding = 0, std140) uniform LightProbe { vec3 lightProbe[9]; };

  vec3 evaluateLightProbe(vec3 probe[9], vec3 dir) {
    return
      .88622692545276 * probe[0] +

      1.0233267079465 * probe[1] * dir.y +
      1.0233267079465 * probe[2] * dir.z +
      1.0233267079465 * probe[3] * dir.x +

      .85808553080978 * probe[4] * dir.x * dir.y +
      .85808553080978 * probe[5] * dir.y * dir.z +
      .24770795610038 * probe[6] * (3. * dir.z * dir.z - 1.) +
      .85808553080978 * probe[7] * dir.x * dir.z +
      .42904276540489 * probe[8] * (dir.x * dir.x - dir.y * dir.y)
    ;
  }
  vec4 lovrmain() {
    vec3 lpc = evaluateLightProbe(lightProbe, normalize(Normal));
    float bias = 0;
    float scl = 1;
    lpc = (lpc - bias) * scl + bias;
    return vec4(lpc, 1.);
  }
]])

probe = lovr.math.newLightProbe()

light_pos = lovr.math.newVec3(0, 10, 0)

function drawLight(pass)
  local t = lovr.timer.getTime() * 0.2
  pass:setColor(1,1,1)
  pass:sphere(light_pos, 2)
end

function lovr.update(dt)
  if lovr.headset.isDown('left', 'trigger') then
    local v = vec3(quat(lovr.headset.getOrientation('left')):direction()):mul(5)
    light_pos:lerp(v, dt)
  end
  local t = lovr.timer.getTime()
  if     lovr.system.isKeyDown('1') then
    light_pos:lerp(0, 1, 0, dt * 4):normalize():mul(5)
  elseif lovr.system.isKeyDown('2') then
    light_pos:lerp(1, 0, 0, dt * 4):normalize():mul(5)
  elseif lovr.system.isKeyDown('3') then
    light_pos:lerp(0, -1, 0, dt * 4):normalize():mul(5)
  end
  box:bake(drawLight)
  probe = lovr.math.newLightProbe(box.images)
  probe:scale(1 / math.pi)
end


function lovr.draw(pass)
  pass:skybox(box.cubetex)
  pass:setColor(0.2, 0.2, 0.2)
  pass:setColor(1,1,1)
  pass:setShader(probeShader)
  pass:send('LightProbe', lovr.graphics.getBuffer(probe:getCoefficients(), {'vec3s', layout='std140'}))
  pass:monkey(mat4(0, 0, -1):scale(0.3))
end