From e98af7966f1cb3071806f8124dceea1a4c4c45d2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Sat, 3 Jun 2023 21:14:11 +0300
Subject: [PATCH] Smoother missile tail fade

---
 bundle/main.lua | 47 +++++++++++++++++++++++++++++------------------
 1 file changed, 29 insertions(+), 18 deletions(-)

diff --git a/bundle/main.lua b/bundle/main.lua
index d9cc55e..4617d89 100644
--- a/bundle/main.lua
+++ b/bundle/main.lua
@@ -7,7 +7,9 @@ local wall_thickness = 0.01
 
 local missiles = {}
 local missile_radius = 0.005
-local missile_trail_length = 15
+local missile_trail_fade = 0.4
+local missile_trail_min_visibility = 0.03
+local missile_trail_length = math.log(missile_trail_min_visibility, missile_trail_fade)
 
 local cities = {}
 local city_radius = 0.05
@@ -102,6 +104,7 @@ function spawnMissile(x, y, target_x, target_y, speed)
 		history = {
 			{x = x, y = y}
 		},
+		trail_length = 0,
 		alive = true
 	})
 end
@@ -130,25 +133,20 @@ function updateMissiles(dt)
 		missile.x = missile.x + missile.dx * dt
 		missile.y = missile.y + missile.dy * dt
 
-		local collided = false
-
 		if missile.y < wall_thickness + missile_radius then
 			-- Collision with top wall
 			missile.y = wall_thickness + missile_radius
 			missile.dy = -missile.dy
-			collided = true
 		end
 
 		if missile.x < wall_thickness + missile_radius then
 			-- Collision with left wall
 			missile.x = wall_thickness + missile_radius
 			missile.dx = -missile.dx
-			collided = true
 		elseif missile.x > 1 - (wall_thickness + missile_radius) then
 			-- Collision with right wall
 			missile.x = 1 - (wall_thickness + missile_radius)
 			missile.dx = -missile.dx
-			collided = true
 		end
 
 		local paddle_left = paddle_x - paddle_width/2
@@ -159,7 +157,6 @@ function updateMissiles(dt)
 			missile.y = paddle_top
 			missile.dy = -missile.dy
 			missile.reflected = true
-			collided = true
 		end
 
 		for _, city in ipairs(cities) do
@@ -188,16 +185,23 @@ function updateMissiles(dt)
 			end
 		end
 
-		if collided then
-			table.insert(missile.history, 1, {
-				x = missile.x,
-				y = missile.y
-			})
-			-- Remove the oldest segments
-			if #missile.history > missile_trail_length then
-				table.remove(missile.history)
-			end
+		local dx = missile.history[1].x - missile.x
+		local dy = missile.history[1].y - missile.y
+		local distance = math.sqrt(dx * dx + dy * dy)
+		missile.history[1].length = distance
+		missile.trail_length = missile.trail_length + distance
+		table.insert(missile.history, 1, {
+			x = missile.x,
+			y = missile.y,
+			length = nil,
+		})
+		-- Remove the oldest segments
+		while missile.trail_length > missile_trail_length do
+			local length = missile.history[#missile.history].length
+			missile.trail_length = missile.trail_length - length
+			table.remove(missile.history)
 		end
+		print(#missile.history)
 	end
 
 	local i = 1
@@ -335,16 +339,23 @@ function drawMissiles()
 
 	-- Trails
 	for _, missile in ipairs(missiles) do
+		local dx = missile.history[1].x - missile.x
+		local dy = missile.history[1].y - missile.y
+		local length = math.sqrt(dx * dx + dy * dy)
+
 		local from_x, from_y = toScreenCoordinates(missile.x, missile.y)
-		local visibility = 1
 		for _, point in ipairs(missile.history) do
+			local visibility = missile_trail_fade ^ length
+			if point.length ~= nil then
+				length = length + point.length
+			end
+
 			local x, y = toScreenCoordinates(point.x, point.y)
 			if missile.reflected then
 				love.graphics.setColor(1 * visibility, 1 * visibility, 0.5 * visibility)
 			else
 				love.graphics.setColor(1 * visibility, 0.4 * visibility, 0 * visibility)
 			end
-			visibility = visibility * 0.8
 			love.graphics.line(from_x, from_y, x, y)
 			from_x = x
 			from_y = y