nudge colliding definitions aside when moving

Implementation copied from:
  https://akkartik.itch.io/carousel/devlog/649349/handling-cascading-collisions

0006-on.mouse_press

@@ -25,9 +25,10 @@ on.mouse_press = function(x,y, mouse_button)
 	local node = on_handle(x,y)
 	if node then
 		-- move node
+		prepare_to_move()
 		Move = {xoff=App.mouse_x()-vx(node.x), yoff=App.mouse_y()-vy(node.y), node=node}
 		return
 	end
 	-- pan surface
 	Pan = {x=Viewport.x+x/Viewport.zoom, y=Viewport.y+y/Viewport.zoom}
-end
+end

0018-on.update

@@ -23,6 +23,9 @@ on.update = function(dt)
 		-- quantize the x axis to discrete columns
 		Move.node.x = round(Move.node.x/100)*100
 		A1(Move.node.key)
+		Move.node.pos.x = Move.node.x+Move.node.w/2
+		Move.node.pos.y = Move.node.y+Move.node.h/2
+		move_others(Move.node)
 		return
 	end
-end
+end

0127-collide

@@ -0,0 +1,15 @@
+-- returns the _minimum separation vector_ if there's a collision
+-- requires a pos+halfsize representation for nodes
+collide = function(a, b)
+	local delta = {x=a.pos.x-b.pos.x, y=a.pos.y-b.pos.y}
+	local abs_delta = {x=math.abs(a.pos.x-b.pos.x), y=math.abs(a.pos.y-b.pos.y)}
+	local size = {x=a.hs.x+b.hs.x, y=a.hs.y+b.hs.y}
+	local abs_amount = {x=size.x-abs_delta.x, y=size.y-abs_delta.y}
+	if abs_amount.x > 0 and abs_amount.y > 0 then
+		if abs_amount.x <= abs_amount.y then
+			return {x=abs_amount.x*sign(delta.x), y=0}
+		else 
+			return {x=0, y=abs_amount.y*sign(delta.y)}
+		end
+	end
+end

0128-move_others

@@ -0,0 +1,13 @@
+-- move any colliding Rects to make room for `a`
+move_others = function(a)
+	for _,d in pairs(Definitions) do
+		if d ~= a then
+			local msv = collide(a, d)
+			if msv then
+				move(d, msv)
+				A1(d.key)
+				move_others(d)
+			end
+		end
+	end
+end

0129-prepare_to_move

@@ -0,0 +1,12 @@
+prepare_to_move = function()
+	for _,def in pairs(Definitions) do
+		assert(def.w)
+		assert(def.h)
+		if def.pos == nil then def.pos = {} end
+		if def.hs == nil then def.hs = {} end
+		def.pos.x = def.x + def.w/2
+		def.pos.y = def.y + def.h/2
+		def.hs.x = def.w/2
+		def.hs.y = def.h/2
+	end
+end

0130-move

@@ -0,0 +1,6 @@
+move = function(def, msv)
+	def.x = def.x - msv.x
+	def.y = def.y - msv.y
+	def.pos.x = def.pos.x - msv.x
+	def.pos.y = def.pos.y - msv.y
+end

0131-sign

@@ -0,0 +1,5 @@
+sign = function(v)
+  if v < 0 then return -1 end
+  if v > 0 then return 1 end
+  return 0
+end