Make animation speed independent of config.fps, add config.animation_rate to fine-tune animation speed (#93)

* animation rate config field

* @franko's math magic to make it look more correct

data/core/config.lua

@@ -19,6 +19,7 @@ config.line_limit = 80
 config.max_symbols = 4000
 config.max_project_files = 2000
 config.transitions = true
+config.animation_rate = 1.0
 config.blink_period = 0.8
 
 -- Disable plugin loading setting to false the config entry

data/core/view.lua

@@ -24,7 +24,10 @@ function View:move_towards(t, k, dest, rate)
   if not config.transitions or math.abs(val - dest) < 0.5 then
     t[k] = dest
   else
-    t[k] = common.lerp(val, dest, rate or 0.5)
+    rate = common.clamp(rate or 0.5, 1e-8, 1 - 1e-8)
+    local alpha = math.log(1 - rate) * config.animation_rate
+    local dt = 60 / config.fps
+    t[k] = common.lerp(val, dest, 1 - math.exp(alpha * dt))
   end
   if val ~= dest then
     core.redraw = true