A testbed for light probe generation from a dynamically rendered skybox

lightprobe_skybox.lua

local shh = require'shh'  -- grab from https://github.com/bjornbytes/shh

-- a newer version of skybox might be available https://github.com/jmiskovic/lovr-atmo
local skybox = {}
skybox.__index = skybox

local cubemap_transforms = {
  Mat4():lookAt(vec3(0, 0, 0), vec3( 1, 0, 0), vec3(0, 1, 0)),
  Mat4():lookAt(vec3(0, 0, 0), vec3(-1, 0, 0), vec3(0, 1, 0)),
  Mat4():lookAt(vec3(0, 0, 0), vec3( 0, 1, 0), vec3(0, 0,-1)),
  Mat4():lookAt(vec3(0, 0, 0), vec3( 0,-1, 0), vec3(0, 0, 1)),
  Mat4():lookAt(vec3(0, 0, 0), vec3( 0, 0, 1), vec3(0, 1, 0)),
  Mat4():lookAt(vec3(0, 0, 0), vec3( 0, 0,-1), vec3(0, 1, 0))
}

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', 'storage'}})
  self.horizon_color = lovr.math.newVec3()
  return self
end


function skybox:bake(drawfn)
  -- render scene to cubemap texture
  self.render_pass = self.render_pass or lovr.graphics.newPass({self.cubetex, samples=1})
  self.render_pass:reset()
  local projection = mat4():perspective(math.pi / 2, 1, 0, 0)
  for i, transform in ipairs(cubemap_transforms) do
    self.render_pass:setProjection(i, projection)
    self.render_pass:setViewPose(i, transform)
  end
  drawfn(self.render_pass)
  lovr.graphics.submit(self.render_pass)
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.);
  }
]])

sh = shh.new()

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

function drawLight(pass)
  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)
    v.x = -v.x -- TODO: this shouldn't be needed, something's off in skybox
    v.z = -v.z
    light_pos:lerp(v, dt)
  end
  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)
  sh = shh.new(box.cubetex)
end


function lovr.draw(pass)
  pass:skybox(box.cubetex)
  pass:setColor(0.2, 0.2, 0.2)
  pass:setColor(1,1,1)
  shh.setShader(pass, sh)
  pass:monkey(mat4(0, 1, -3))
end