From f3cc0907c8e345882b0d98fda74f4ed47fe96326 Mon Sep 17 00:00:00 2001
From: Eric Wasylishen <ewasylishen@gmail.com>
Date: Wed, 2 Nov 2022 00:56:23 -0600
Subject: [PATCH] faceextents_t: refactor to remove lightmapshift member

---
 common/bsputils.cc         | 17 ++++++++++++++---
 include/common/bsputils.hh |  3 ++-
 tests/test_ltface.cc       | 13 +++++++++++++
 3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/common/bsputils.cc b/common/bsputils.cc
index 63afe36a..2c195d24 100644
--- a/common/bsputils.cc
+++ b/common/bsputils.cc
@@ -682,7 +682,7 @@ qmat4x4f TexSpaceToWorld(const mbsp_t *bsp, const mface_t *f)
 
 // faceextents_t
 
-faceextents_t::faceextents_t(const mface_t &face, const mbsp_t &bsp, float lmshift) : lightmapshift(lmshift)
+faceextents_t::faceextents_t(const mface_t &face, const mbsp_t &bsp, float lightmapshift)
 {
     worldToTexCoordMatrix = WorldToTexSpace(&bsp, &face);
     texCoordToWorldMatrix = TexSpaceToWorld(&bsp, &face);
@@ -731,6 +731,13 @@ faceextents_t::faceextents_t(const mface_t &face, const mbsp_t &bsp, float lmshi
 
     origin = bounds.mins() + radius;
     this->radius = qv::length(radius);
+
+    LMToTexCoordMatrix = qmat3x3f::row_major({
+        lightmapshift, 0,             texmins[0] * lightmapshift,
+        0            , lightmapshift, texmins[1] * lightmapshift,
+        0            , 0            , 1
+    });
+    TexCoordToLMMatrix = qv::inverse(LMToTexCoordMatrix);
 }
 
 int faceextents_t::width() const
@@ -755,12 +762,16 @@ qvec2i faceextents_t::texsize() const
 
 qvec2f faceextents_t::lightmapCoordToTexCoord(const qvec2f &LMCoord) const
 {
-    return {lightmapshift * (texmins[0] + LMCoord[0]), lightmapshift * (texmins[1] + LMCoord[1])};
+    qvec3f LMCoordPadded = {LMCoord[0], LMCoord[1], 1.0f};
+    qvec2f tex = LMToTexCoordMatrix * LMCoordPadded;
+    return tex;
 }
 
 qvec2f faceextents_t::texCoordToLightmapCoord(const qvec2f &tc) const
 {
-    return {(tc[0] / lightmapshift) - texmins[0], (tc[1] / lightmapshift) - texmins[1]};
+    qvec3f tcPadded = {tc[0], tc[1], 1.0f};
+    qvec2f lm = TexCoordToLMMatrix * tcPadded;
+    return lm;
 }
 
 qvec2f faceextents_t::worldToTexCoord(qvec3f world) const
diff --git a/include/common/bsputils.hh b/include/common/bsputils.hh
index 1444fcb2..3b600abe 100644
--- a/include/common/bsputils.hh
+++ b/include/common/bsputils.hh
@@ -125,9 +125,10 @@ class faceextents_t
 public:
     qvec2i texmins;
     qvec2i texextents;
-    float lightmapshift;
     qmat4x4f worldToTexCoordMatrix;
     qmat4x4f texCoordToWorldMatrix;
+    qmat3x3f LMToTexCoordMatrix;
+    qmat3x3f TexCoordToLMMatrix;
 
     qvec3d origin;
     vec_t radius;
diff --git a/tests/test_ltface.cc b/tests/test_ltface.cc
index e8b5f77a..14593d05 100644
--- a/tests/test_ltface.cc
+++ b/tests/test_ltface.cc
@@ -1,6 +1,7 @@
 #include <doctest/doctest.h>
 
 #include <light/light.hh>
+#include <common/bspinfo.hh>
 #include <qbsp/qbsp.hh>
 #include <testmaps.hh>
 
@@ -39,6 +40,18 @@ static void LoadTestmap(const std::filesystem::path &name, std::vector<std::stri
         };
         light_main(light_args);
     }
+
+    // serialize obj
+    {
+        bspdata_t bspdata;
+        LoadBSPFile(bsp_path, &bspdata);
+
+        ConvertBSPFormat(&bspdata, &bspver_generic);
+
+        // write to .json for inspection
+        serialize_bsp(bspdata, std::get<mbsp_t>(bspdata.bsp),
+            fs::path(qbsp_options.bsp_path).replace_extension(".bsp.json"));
+    }
 }
 
 TEST_CASE("TestLight") {