From eb3a654c6768b07e95ed08fa9a91217a3c2ceb39 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Fri, 28 Jun 2019 23:59:41 +0300
Subject: [PATCH] Fix visibility (mostly)

---
 bundle/main.lua | 84 +++++++++++++++++++++++++++++++++++--------------
 1 file changed, 61 insertions(+), 23 deletions(-)

diff --git a/bundle/main.lua b/bundle/main.lua
index 586ddf5..bed6ac2 100644
--- a/bundle/main.lua
+++ b/bundle/main.lua
@@ -247,51 +247,89 @@ function generateVisibilityMap()
 end
 
 function stepVisibilityMapGeneration(queue)
-	-- TODO: Handle corners somehow correctly
 	-- Do a modified floodfill, where each cell will only expand in its given direction, not
 	-- every direction like in a normal floodfill
 	local new_queue = {}
 
 	for i, item in ipairs(queue) do
-		visibility_map[item.x][item.y] = true
-
 		if cavern[item.x][item.y] == tiletypes.empty then
 			-- Did not yet hit a wall
 			if item.direction == directions.up then
+				visibility_map[item.x][item.y] = true
 				table.insert(new_queue, {x = item.x, y = item.y - 1, direction = directions.up})
 			elseif item.direction == directions.left then
+				visibility_map[item.x][item.y] = true
 				table.insert(new_queue, {x = item.x - 1, y = item.y, direction = directions.left})
 			elseif item.direction == directions.down then
+				visibility_map[item.x][item.y] = true
 				table.insert(new_queue, {x = item.x, y = item.y + 1, direction = directions.down})
 			elseif item.direction == directions.right then
+				visibility_map[item.x][item.y] = true
 				table.insert(new_queue, {x = item.x + 1, y = item.y, direction = directions.right})
 			elseif item.direction == directions.upleft then
-				--     ⌜^
-				-- ⌜   <x
-				table.insert(new_queue, {x = item.x - 1, y = item.y - 1, direction = directions.upleft})
-				table.insert(new_queue, {x = item.x, y = item.y - 1, direction = directions.up})
-				table.insert(new_queue, {x = item.x - 1, y = item.y, direction = directions.left})
+				-- Check that we could have gotten here also by moving only 4-ways
+				--
+				-- The possible cases are:
+				-- (o represents old position, x is new, and # is a wall)
+				--
+				-- x    x#   x    x#
+				--  o    o   #o   #o
+				--
+				-- In the first three, the movement is possible, but in the last one
+				-- it is not. We can therefore check whether the movement is valid
+				-- by testing if either the cell to our right or below us (the
+				-- directions opposite to the ones in an up.left movement) is empty
+				if cavern[item.x + 1][item.y] == tiletypes.empty or cavern[item.x][item.y + 1] == tiletypes.empty then
+					--     ⌜^
+					-- ⌜   <x
+					visibility_map[item.x][item.y] = true
+					table.insert(new_queue, {x = item.x - 1, y = item.y - 1, direction = directions.upleft})
+					table.insert(new_queue, {x = item.x, y = item.y - 1, direction = directions.up})
+					table.insert(new_queue, {x = item.x - 1, y = item.y, direction = directions.left})
+				end
 			elseif item.direction == directions.downleft then
-				-- ⌞   <x
-				--     ⌞v
-				table.insert(new_queue, {x = item.x - 1, y = item.y, direction = directions.left})
-				table.insert(new_queue, {x = item.x - 1, y = item.y + 1, direction = directions.downleft})
-				table.insert(new_queue, {x = item.x, y = item.y + 1, direction = directions.down})
+				-- See under item.direction == directions.upleft
+				if cavern[item.x + 1][item.y] == tiletypes.empty or cavern[item.x][item.y - 1] == tiletypes.empty then
+					-- ⌞   <x
+					--     ⌞v
+					visibility_map[item.x][item.y] = true
+					table.insert(new_queue, {x = item.x - 1, y = item.y, direction = directions.left})
+					table.insert(new_queue, {x = item.x - 1, y = item.y + 1, direction = directions.downleft})
+					table.insert(new_queue, {x = item.x, y = item.y + 1, direction = directions.down})
+				end
 			elseif item.direction == directions.downright then
-				-- ⌟   x>
-				--     v⌟
-				table.insert(new_queue, {x = item.x + 1, y = item.y, direction = directions.right})
-				table.insert(new_queue, {x = item.x, y = item.y + 1, direction = directions.down})
-				table.insert(new_queue, {x = item.x + 1, y = item.y + 1, direction = directions.downright})
+				-- See under item.direction == directions.upleft
+				if cavern[item.x - 1][item.y] == tiletypes.empty or cavern[item.x][item.y - 1] == tiletypes.empty then
+					-- ⌟   x>
+					--     v⌟
+					visibility_map[item.x][item.y] = true
+					table.insert(new_queue, {x = item.x + 1, y = item.y, direction = directions.right})
+					table.insert(new_queue, {x = item.x, y = item.y + 1, direction = directions.down})
+					table.insert(new_queue, {x = item.x + 1, y = item.y + 1, direction = directions.downright})
+				end
 			elseif item.direction == directions.upright then
-				--     ^⌝
-				-- ⌝   x>
-				table.insert(new_queue, {x = item.x, y = item.y - 1, direction = directions.up})
-				table.insert(new_queue, {x = item.x + 1, y = item.y - 1, direction = directions.upright})
-				table.insert(new_queue, {x = item.x + 1, y = item.y, direction = directions.right})
+				-- See under item.direction == directions.upleft
+				if cavern[item.x - 1][item.y] == tiletypes.empty or cavern[item.x][item.y + 1] == tiletypes.empty then
+					--     ^⌝
+					-- ⌝   x>
+					visibility_map[item.x][item.y] = true
+					table.insert(new_queue, {x = item.x, y = item.y - 1, direction = directions.up})
+					table.insert(new_queue, {x = item.x + 1, y = item.y - 1, direction = directions.upright})
+					table.insert(new_queue, {x = item.x + 1, y = item.y, direction = directions.right})
+				end
 			else
 				error("Visibility floodfill item travelling in an impossible direction")
 			end
+		else
+			-- Hit a wall
+			if item.direction == directions.up or
+			   item.direction == directions.left or
+			   item.direction == directions.down or
+			   item.direction == directions.right then
+				-- Only draw it as visible if we reached it with a non-diagonal move
+				-- because diagonals might have been non-valid moves
+				visibility_map[item.x][item.y] = true
+			end
 		end
 	end