From c043bb8ecfae0aed494d1c76e973b006d361824a Mon Sep 17 00:00:00 2001
From: Kazhnuz <antoine@sortilege.net>
Date: Mon, 1 Jul 2019 18:06:25 +0200
Subject: [PATCH] feat(actor3D): add zSorting support

---
 gamecore/modules/world/world3D.lua | 99 ++++++++++++++++++++++++++----
 1 file changed, 88 insertions(+), 11 deletions(-)

diff --git a/gamecore/modules/world/world3D.lua b/gamecore/modules/world/world3D.lua
index 06813db..e910d13 100644
--- a/gamecore/modules/world/world3D.lua
+++ b/gamecore/modules/world/world3D.lua
@@ -29,6 +29,7 @@ local World3D   = BaseWorld:extend()
 local Sti           = require(cwd .. "libs.sti")
 local Bump          = require(cwd .. "libs.bump")
 local Bump3D        = require(cwd .. "libs.bump-3dpd")
+local Tsort         = require(cwd .. "libs.tsort")
 local CameraSystem  = require(cwd .. "camera")
 
 local PADDING_VALUE = 10/100
@@ -79,17 +80,7 @@ function BaseWorld:getVisibleActors(id)
     actors = self:getActors()
   end
 
-  table.sort(actors, function(a,b)
-    if (a.y == b.y) then
-      if (a.depth == b.depth) then
-        return a.creationID < b.creationID
-      else
-        return a.depth > b.depth
-      end
-    else
-      return a.y < b.y
-    end
-  end)
+  actors = self:zSortItems(actors)
 
   return actors
 end
@@ -199,4 +190,90 @@ function World3D:getShapeInRect(x, y, w, h)
   return self.shapes:queryRect(x, y, w, h)
 end
 
+-- DRAW FUNCTIONS
+-- Functions to draw the world
+
+function World3D:zSortItems(items)
+  -- zSorting algorithm taken from bump3D example, adapted to gamecore.
+  local graph = Tsort.new()
+  local noOverlap = {}
+
+  -- Iterate through all visible items, and calculate ordering of all pairs
+  -- of overlapping items.
+  -- TODO: Each pair is calculated twice currently. Maybe this is slow?
+  for _, itemA in ipairs(items) do repeat
+    local x, y, w, h = self.shapes:getRect(itemA)
+    local otherItemsFilter = function(other) return other ~= itemA end
+    local overlapping, len = self.shapes:queryRect(x, y, w, h, otherItemsFilter)
+
+    if len == 0 then
+      table.insert(noOverlap, itemA)
+
+      break
+    end
+
+    local _, aY, aZ, _, aH, aD = self.bodies:getCube(itemA.mainHitbox)
+    aDepth  = itemA.depth
+    aID     = itemA.id
+    aType   = itemA.type
+    aZ     = math.ceil(aZ)
+    aY     = math.ceil(aY)
+
+    for _, itemB in ipairs(overlapping) do
+      local _, bY, bZ, _, bH, bD = self.bodies:getCube(itemB.mainHitbox)
+      bDepth = itemB.depth
+      bID    = itemB.id
+      bType  = itemB.type
+      bZ     = math.ceil(bZ)
+      bY     = math.ceil(bY)
+
+      if aZ >= bZ + bD then
+        -- item A is completely above item B
+        graph:add(itemB, itemA)
+      elseif bZ >= aZ + aD then
+        -- item B is completely above item A
+        graph:add(itemA, itemB)
+      elseif aY + aH <= bY then
+        -- item A is completely behind item B
+        graph:add(itemA, itemB)
+      elseif bY + bH <= aY then
+        -- item B is completely behind item A
+        graph:add(itemB, itemA)
+      elseif (aY - aZ) + aH > (bY - bZ) + bH then
+        -- item A's forward-most point is in front of item B's forward-most point
+        graph:add(itemB, itemA)
+      elseif (aY - aZ) + aH < (bY - bZ) + bH then
+        -- item B's forward-most point is in front of item A's forward-most point
+        graph:add(itemA, itemB)
+      else
+        -- item A's forward-most point is the same than item B's forward-most point
+        if aDepth > bDepth then
+          graph:add(itemB, itemA)
+        elseif aDepth < bDepth then
+          graph:add(itemA, itemB)
+        else
+          if aID > bID then
+            graph:add(itemA, itemB)
+          elseif aID < bID then
+            graph:add(itemB, itemA)
+          else
+            err("two object can't have the same ID")
+          end
+        end
+      end
+    end
+  until true end
+
+  local sorted, err = graph:sort()
+  if err then
+    error(err)
+  end
+  for _, item in ipairs(noOverlap) do
+    table.insert(sorted, item)
+  end
+
+  return sorted
+
+end
+
 return World3D