Walk-in-place locomotion example

examples/Locomotion/Walking_In_Place/main.lua

@@ -0,0 +1,101 @@
+-- Walk or jog in place to move forward
+
+local motion = {
+  pose = lovr.math.newMat4(), -- Transformation in VR initialized to origin (0,0,0) looking down -Z
+  -- Walk in place parameters
+  amplification = 25, -- Walking speed compared to head bob intensity
+  damping = 0.15,     -- Lower value adds inertia, higher value makes walking less "floaty"
+  -- State
+  speed = 0,
+  headPitch = 0,
+  warmup = 0,
+}
+
+-- IIR filter section (direct II form) ------------------------------------------------------------
+local formII
+formII = {
+  new = function(a, b)
+    local self = setmetatable({}, formII)
+    self.a1, self.a2 = a[2], a[3]                 -- a coefficients (denominator)
+    self.b0, self.b1, self.b2 = b[1], b[2], b[3]  -- b coefficients (nominator)
+    self.v0, self.v1, self.v2 = 0, 0, 0           -- mid-point calculation and its delays
+    return self
+  end,
+  process = function(self, x)
+    self.v2, self.v1 = self.v1, self.v0                               -- process delays
+    self.v0 = x - self.a1 * self.v1 - self.a2 * self.v2               -- mid-value
+    return self.b0 * self.v0 + self.b1 * self.v1 + self.b2 * self.v2  -- output
+  end,
+}
+formII.__index = formII ---------------------------------------------------------------------------
+
+-- Construct a band-pass filter
+--  Coefficients obtained with `butter(1, [1.5,2.8], 'bandpass', False, 'sos', 60)` from scipy.signal
+motion.filterSection1 = formII.new({1.0, -1.8587017, 0.9066295}, {0.0029759,  0.0059517, 0.0029759})
+motion.filterSection2 = formII.new({1.0, -1.9198555, 0.9394925}, {1.0000000, -2.0000000, 1.0000000})
+
+function motion.walkinplace(dt)
+  local _, y, _ = lovr.headset.getPosition('head')
+  -- Warm-up phase allows filter to settle in while adapting to user height
+  if motion.warmup < 0.5 then
+    for i = 1, 20 do
+      motion.filterSection2:process(motion.filterSection1:process(y))
+    end
+    motion.warmup = motion.warmup + dt
+    return
+  end
+  local direction = quat(lovr.headset.getOrientation('head')):direction()
+  local pitch = direction.y
+  -- Detect pitch changes (looking up/down) and inhibit walking until pitch motion ends
+  motion.headPitch = ((pitch - motion.headPitch) * 0.1 + motion.headPitch)
+  local pitchChange = math.abs(pitch - motion.headPitch) * 10
+  local walkInhibit = math.max(1 - pitchChange, 0)
+  -- Estimate intensity of head bob due to walking or jogging
+  --  Filter y signal with bandpass to isolate frequencies around 2 Hz
+  --  Take absolute value of signal and amplify with parameter
+  local filtered = motion.filterSection2:process(motion.filterSection1:process(y))
+  local walkIntensity = math.abs(filtered) * motion.amplification
+  -- Apply estimated walk intensity to speed
+  -- Simple lowpass IIR is applied for smoothness and inertia
+  motion.speed = motion.speed * (1 - motion.damping) + walkIntensity * walkInhibit
+  direction.y = 0
+  motion.pose:translate(direction * motion.speed * dt)
+end
+
+
+function lovr.update(dt)
+  motion.walkinplace(dt)
+end
+
+function lovr.draw()
+  lovr.graphics.setBackgroundColor(0.1, 0.1, 0.1)
+  lovr.graphics.print(string.format('%2.3f', motion.speed), 19, 1, -15, 0.05)
+  lovr.graphics.transform(mat4(motion.pose):invert())
+  -- Render hands
+  lovr.graphics.setColor(1,1,1)
+  local radius = 0.04
+  for _, hand in ipairs(lovr.headset.getHands()) do
+    -- Whenever pose of hand or head is used, need to account for VR movement
+    local poseRW = mat4(lovr.headset.getPose(hand))
+    local poseVR = mat4(motion.pose):mul(poseRW)
+    poseVR:scale(radius)
+    lovr.graphics.sphere(poseVR)
+  end
+  -- Some scenery
+  lovr.math.setRandomSeed(0)
+  local goldenRatio = (math.sqrt(5) + 1) / 2
+  local goldenAngle = (2 - goldenRatio) * (2 * math.pi)
+  local k = 1.8
+  for i = 1, 500 do
+    local r = math.sqrt(i) * k
+    local x = math.cos(goldenAngle * i) * r
+    local y = math.sin(goldenAngle * i) * r
+    if lovr.math.random() < 0.05 then
+      lovr.graphics.setColor(0.5, 0, 0)
+    else
+      local shade = 0.1 + 0.3 * lovr.math.random()
+      lovr.graphics.setColor(shade, shade, shade)
+    end
+    lovr.graphics.cylinder(x, -0.01, y,  0.02, math.pi / 2, 1,0,0, 1, 1)
+  end
+end