From 0abc0b9b7928cd72b1c92b3af9f30674397013d1 Mon Sep 17 00:00:00 2001
From: ubq323 <ubq323@ubq323.website>
Date: Mon, 13 Feb 2023 01:18:57 +0000
Subject: add collisions and sliding for player movement

---
 client/movement.lua | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 client/movement.lua

(limited to 'client/movement.lua')

diff --git a/client/movement.lua b/client/movement.lua
new file mode 100644
index 0000000..78af5f0
--- /dev/null
+++ b/client/movement.lua
@@ -0,0 +1,92 @@
+local Pos = require"common.coords".Pos
+
+local function sign(x)
+	if x == 0 then return 0
+	elseif x <  0 then return -1
+	elseif x > 	0 then return 1
+	end
+end
+local function clamp(x,minv,maxv)
+	return math.min(math.max(x,minv),maxv)
+end
+
+	
+
+-- https://iquilezles.org/articles/distgradfunctions2d/
+local function iqz_hex_sdgf(px,py, r)
+	local kx,ky,kz = -0.866025404,0.5,0.577350269
+	local sx,sy = sign(px),sign(py)
+	px = math.abs(px)
+	py = math.abs(py)
+	local w = kx*px+ky*py
+	
+	local _1 = 2*math.min(w,0)
+	px = px - _1*kx
+	py = py - _1*ky
+
+	px = px - clamp(px,-kz*r,kz*r)
+	py = py - r
+
+	d = math.sqrt(px*px+py*py)*sign(py)
+
+	local gx,gy
+	if w<0 then
+		gx = -ky*px - kx*py
+		gy = -kx*px + ky*py
+	else
+		gx,gy = px,py
+	end
+
+	-- dist, gradx, grady
+	return d, sx*gx/d, sy*gy/d
+
+end
+
+
+-- rotate by 30 degrees
+local c30,s30 = math.cos(math.rad(30)), math.sin(math.rad(30))
+local function  t_in(x,y) return c30*x-s30*y,  s30*x+c30*y end
+local function t_out(x,y) return c30*x+s30*y, -s30*x+c30*y end
+
+-- above sdf has flat top not pointy-top hexagons
+-- so need to rotate
+-- also, 'r' parameter in the above seems to be distance to side
+-- but in our unit system, 1 unit is distance to vertex
+-- conversion factor between these is also cos(30deg)
+-- this is distance to hex at 0,0
+local function hex_sdgf_00(pos)
+	local tpx,tpy = t_in(pos.x,pos.y)
+	local d,gx,gy = iqz_hex_sdgf(tpx,tpy,c30)
+	return d, t_out(gx,gy)
+end
+
+local function hex_sdgf(pos, hex)
+	return hex_sdgf_00(pos-hex:to_pos())
+end
+
+local PLAYER_SIZE = 0.35
+local function collide_with_terrain(old_pos, try_pos, map, tries_remaining)
+	tries_remaining = tries_remaining or 3
+	if tries_remaining <= 0 then return old_pos end
+	local try_h = try_pos:to_hex():round()
+	for near_h in try_h:iter_neighbours(1) do
+		local tile = map:at(near_h)
+		if tile then
+			local d,gx,gy = hex_sdgf(try_pos, near_h)
+			if d < PLAYER_SIZE then
+				local push_dist = PLAYER_SIZE - d
+				local push_dir = Pos:make(gx,gy)
+				local new_try_pos = try_pos + (push_dist*push_dir)
+				return collide_with_terrain(old_pos,new_try_pos,map,tries_remaining-1)
+			end
+		end
+	end
+
+	return try_pos
+end
+
+
+return {
+	collide_with_terrain = collide_with_terrain,
+	hex_sdgf=hex_sdgf
+}
-- 
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