From f7dbb1a8845ed4071f32b4ca6f62519ce5e35dd6 Mon Sep 17 00:00:00 2001
From: HybridDog <ovvv@web.de>
Date: Fri, 27 Mar 2020 18:17:25 +0100
Subject: [PATCH] Add (unoptimized) vector.triangle

---
 init.lua | 107 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 106 insertions(+), 1 deletion(-)

diff --git a/init.lua b/init.lua
index 3a621fd..b2cd9d4 100644
--- a/init.lua
+++ b/init.lua
@@ -6,7 +6,8 @@ function funcs.pos_to_string(pos)
 	return "("..pos.x.."|"..pos.y.."|"..pos.z..")"
 end
 
-local r_corr = 0.25 --remove a bit more nodes (if shooting diagonal) to let it look like a hole (sth like antialiasing)
+local r_corr = 0.25 --remove a bit more nodes (if shooting diagonal) to let it
+-- look like a hole (sth like antialiasing)
 
 -- this doesn't need to be calculated every time
 local f_1 = 0.5-r_corr
@@ -1006,6 +1007,110 @@ function funcs.serialize(vec)
 	return "{x=" .. vec.x .. ",y=" .. vec.y .. ",z=" .. vec.z .. "}"
 end
 
+function funcs.triangle(pos1, pos2, pos3)
+	local normal = vector.cross(vector.subtract(pos2, pos1),
+		vector.subtract(pos3, pos1))
+	-- Find the biggest absolute component of the normal vector
+	local dir = vector.get_max_coord({
+		x = math.abs(normal.x),
+		y = math.abs(normal.y),
+		z = math.abs(normal.z),
+	})
+	-- Find the other directions for the for loops
+	local all_other_dirs = {
+		x = {"z", "y"},
+		y = {"z", "x"},
+		z = {"y", "x"},
+	}
+	local other_dirs = all_other_dirs[dir]
+	-- Sort the positions along the other directions
+	--[[
+	local sorteds = {}
+	for i = 1,2 do
+		local odir = other_dirs[i]
+		local ps = {}
+		if pos1[odir] < pos2[odir] then
+			if pos1[odir] < pos3[odir] then
+				ps[1] = pos1
+				if pos2[odir] < pos3[odir] then
+					ps[2] = pos2
+					ps[3] = pos3
+				else
+					ps[3] = pos2
+					ps[2] = pos3
+				end
+			else
+				ps[1] = pos3
+				ps[2] = pos1
+				ps[3] = pos2
+			end
+		elseif pos1[odir] < pos3[odir] then
+			ps[1] = pos2
+			ps[2] = pos1
+			ps[3] = pos3
+		else
+			ps[3] = pos1
+			if pos2[odir] < pos3[odir] then
+				ps[1] = pos2
+				ps[2] = pos3
+			else
+				ps[1] = pos3
+				ps[2] = pos2
+			end
+		end
+		sorteds[i] = ps
+	end
+		--~ p1[i] = sorteds[odir][1][odir]
+		--~ p2[i] = sorteds[odir][3][odir]
+	--]]
+	-- The boundaries of the 2D AABB along other_dirs
+	local odir1, odir2 = other_dirs[1], other_dirs[2]
+	local pos1_2d = {pos1[odir1], pos1[odir2]}
+	local pos2_2d = {pos2[odir1], pos2[odir2]}
+	local pos3_2d = {pos3[odir1], pos3[odir2]}
+	local p1 = {}
+	local p2 = {}
+	for i = 1,2 do
+		p1[i] = math.floor(math.min(pos1_2d[i], pos2_2d[i], pos3_2d[i]))
+		p2[i] = math.ceil(math.max(pos1_2d[i], pos2_2d[i], pos3_2d[i]))
+	end
+	-- The lines along the triangle boundaries
+	--~ local lines = {}
+	--~ local ps2 = sorteds[2]
+	--~ local s = {ps2[1][other_dirs[1]], ps2[1][other_dirs[2]]}
+	--~ local e = {ps2[2][other_dirs[1]], ps2[2][other_dirs[2]]}
+	--~ local line_left = {s[1], s[2], e[1] - s[1], e[2] - s[2]}
+
+	-- https://www.scratchapixel.com/lessons/3d-basic-rendering/rasterization-practical-implementation/rasterization-stage
+	local function edgefunc(p1, p2, pos)
+		return (pos[1] - p1[1]) * (p2[2] - p1[2])
+			- (pos[2] - p1[2]) * (p2[1] - p1[1])
+	end
+	local a_all_inv = 1.0 / edgefunc(pos1_2d, pos2_2d, pos3_2d)
+	-- Calculate the triangle points
+	local points = {}
+	local barycentric_coords = {}
+	local n = 0
+	for v1 = p1[1], p2[1] do
+		for v2 = p1[2], p2[2] do
+			-- Not optimized
+			local p = {v1, v2}
+			local k3 = edgefunc(pos1_2d, pos2_2d, p) * a_all_inv
+			local k1 = edgefunc(pos2_2d, pos3_2d, p) * a_all_inv
+			local k2 = 1 - k1 - k3
+			if k1 >= 0 and k2 >= 0 and k3 >= 0 then
+				-- On triangle
+				local h = math.floor(k1 * pos1[dir] + k2 * pos2[dir] +
+					k3 * pos3[dir] + 0.5)
+				n = n+1
+				points[n] = {[odir1] = v1, [odir2] = v2, [dir] = h}
+				barycentric_coords[n] = {k1, k2, k3}
+			end
+		end
+	end
+	return points, n, barycentric_coords
+end
+
 
 vector_extras_functions = funcs