Merge pull request #61 from ernisto/fix/spring

fix(spring tolerance): guarantee a minimun movement to goal

src/spring.luau

@@ -9,8 +9,6 @@ local update_descendants = graph.update_descendants
 local push_scope_as_child_of = graph.push_scope_as_child_of
 
 local UPDATE_RATE = 120
-local TOLERANCE = 0.001
-local TOLERANCE_VECTOR = vector.create(TOLERANCE, TOLERANCE, TOLERANCE)
 
 type Animatable = number | CFrame | Color3 | UDim | UDim2 | Vector2 | Vector3
 
@@ -232,6 +230,24 @@ local function spring<T>(source: () -> T, period: number?, damping_ratio: number
     end, config
 end
 
+-- luau vectors have f32 for each component, unlike luau number which is f64 
+local FLOAT32_MANTISSA_BITS = 23
+type float32 = number
+
+local function get_min_step(x: float32)
+    local _,exponent = math.frexp(x)
+
+    local lower_mantissa = math.ldexp(1, -FLOAT32_MANTISSA_BITS - 1)
+    return math.ldexp(lower_mantissa, exponent)
+end
+local function get_min_vector_step(goal: vector): vector
+    return vector.create(
+        get_min_step(goal.x),
+        get_min_step(goal.y),
+        get_min_step(goal.z)
+    )
+end
+
 local function step_springs(dt: number)
     for data in springs do
         local k, c,
@@ -241,6 +257,8 @@ local function step_springs(dt: number)
             data.x0_123, data.x1_123, data.v_123,
             data.x0_456, data.x1_456, data.v_456
 
+        if x0_123 == x1_123 and x0_456 == x1_456 then continue end
+
         -- calculate displacement from target
         local dx_123 = x0_123 - x1_123
         local dx_456 = x0_456 - x1_456
@@ -261,9 +279,13 @@ local function step_springs(dt: number)
         local v_123 = u_123 + dv_123
         local v_456 = u_456 + dv_456
 
+        -- guarantee pos < pos + velocity <= goal
+        local a_123 = vector.max(get_min_vector_step(x0_123), vector.abs(v_123) * dt) * vector.sign(v_123)
+        local a_456 = vector.max(get_min_vector_step(x0_456), vector.abs(v_456) * dt) * vector.sign(v_456)
+
         -- calculate new position
-        local x_123 = x0_123 + v_123*dt
+        local x_123 = x0_123 + a_123
-        local x_456 = x0_456 + v_456*dt
+        local x_456 = x0_456 + a_456
 
         data.x0_123, data.x0_456 = x_123, x_456
         data.v_123, data.v_456 = v_123, v_456
@@ -272,21 +294,8 @@ end
 
 local function update_spring_sources()
     for data, output in springs do
-        local x0_123, x1_123, v_123,
+        local x0_123, x0_456 = data.x0_123, data.x0_456
-        x0_456, x1_456, v_456 =
+        if x0_123 == data.x1_123 and x0_456 == data.x1_456 then
-            data.x0_123, data.x1_123, data.v_123,
-            data.x0_456, data.x1_456, data.v_456
-
-        local max_difference = vector.max(
-            vector.abs(x0_123 - x1_123 :: any),
-            vector.abs(x0_456 - x1_456 :: any),
-            vector.abs(v_123 :: any),
-            vector.abs(v_456 :: any),
-            TOLERANCE_VECTOR
-        )
-
-        if max_difference == TOLERANCE_VECTOR then
-            -- close enough to target, unshedule spring and set value to target
             springs[data] = nil
             output.cache = data.source_value
         else