Update spring solver

test/spring-test.luau

@@ -0,0 +1,71 @@
+local vide = require "src/init"
+local testkit = require("test/testkit")
+
+local program_time = os.clock()
+
+local function step(): number
+    local FPS = 60
+    local DT = 1/FPS
+
+    repeat until os.clock() - program_time >= DT
+    program_time += DT
+    return DT
+end
+
+local function main()
+    local source = vide.source
+    local spring = vide.spring
+    local watch = vide.watch
+
+    local TERMINAL_HEIGHT = 73 --* REDUCE IF BAR DOES NOT FIT IN TERMINAL
+    local MIN_ALPHA = 0.3
+    local MAX_ALPHA = 0.7
+
+    local MIN = TERMINAL_HEIGHT * MIN_ALPHA
+    local MAX = TERMINAL_HEIGHT * MAX_ALPHA
+    local OFFSET = TERMINAL_HEIGHT - MAX
+
+    local BLOCK = "█"
+
+    local function remainder_to_block(x)
+        return
+            if x > 7/8 then "█"
+            elseif x > 6/8 then "▇"
+            elseif x > 5/8 then "▆"
+            elseif x > 4/8 then "▅"
+            elseif x > 3/8 then "▄"
+            elseif x > 2/8 then "▃"
+            elseif x > 1/8 then "▂"
+            else "▁"
+    end
+
+    local value = source(MAX)
+    local sprung = spring(value, 1, 0.3)
+
+    watch(function()
+        local v = sprung()
+        local fv = math.floor(v)
+        local reset = "\27[H\27[2J" -- ANSI clear terminal
+        local offset = string.rep("\n", MAX - fv + OFFSET)
+        local bar = testkit.color.gray(remainder_to_block(v - fv) .. "\n" .. string.rep(BLOCK .. "\n", fv))
+        print(reset .. offset .. bar)
+    end)
+
+    local elapsed = 0
+    repeat local dt = step()
+        vide.step(dt)
+
+        local T = 3
+        elapsed += dt
+        while elapsed >= T do
+            elapsed -= T
+            value(value() == MAX and MIN or MAX)
+        end
+
+    until false
+end
+
+main()
+
+
+