From 9b42315ef051745b94eeb31d4680f821779b50a2 Mon Sep 17 00:00:00 2001
From: sanine <sanine.not@pm.me>
Date: Tue, 27 Sep 2022 20:36:05 -0500
Subject: fix off-by-1 bug in face indexing

---
 src/import/import.c           | 11 +++++++++--
 src/import/import_mesh.test.c | 17 +++++++++--------
 2 files changed, 18 insertions(+), 10 deletions(-)

(limited to 'src/import')

diff --git a/src/import/import.c b/src/import/import.c
index a093068..becb1fe 100644
--- a/src/import/import.c
+++ b/src/import/import.c
@@ -15,7 +15,10 @@ int import_file(lua_State *L)
 	char *filename;
 	hs_parse_args(L, hs_str(filename));
 
-	const struct aiScene *scene = aiImportFile(filename, aiProcess_Triangulate | aiProcess_FlipUVs);
+	const struct aiScene *scene = aiImportFile(
+		filename, 
+		aiProcess_Triangulate | aiProcess_FlipUVs
+	);
 	if (scene == NULL)
 		hs_throw_error(L, "failed to load file '%s'", filename);
 	
@@ -53,7 +56,11 @@ static void push_face(lua_State *L, struct aiFace face)
 
 	for (int i=0; i<face.mNumIndices; i++) {
 		/* add one to the index bc lua is 1-indexed */
-		lua_pushinteger(L, face.mIndices[i]+1);
+		/* the above comment is WRONG WRONG WRONG!!
+		 * lua is indeed 1-indexed, but this data is being interpreted
+		 * by *opengl* not lua. we should not add 1!!
+		 */
+		lua_pushinteger(L, face.mIndices[i]);
 		lua_rawseti(L, tbl, i+1);
 	}
 }
diff --git a/src/import/import_mesh.test.c b/src/import/import_mesh.test.c
index fdbfbf0..7dc8624 100644
--- a/src/import/import_mesh.test.c
+++ b/src/import/import_mesh.test.c
@@ -55,18 +55,19 @@ void test_push_face()
 	lily_assert_int_equal(lua_objlen(L, facetbl), 6);
 
 	/* the numbers should be one higher because of lua's 1-indexing */
+	/* WRONG! the numbers should be 0-indexed because they will be interpreted by opengl */
 	lua_rawgeti(L, facetbl, 1);
-	lily_assert_int_equal(lua_tointeger(L, -1), 1);
+	lily_assert_int_equal(lua_tointeger(L, -1), 0);
 	lua_rawgeti(L, facetbl, 2);
-	lily_assert_int_equal(lua_tointeger(L, -1), 2);
+	lily_assert_int_equal(lua_tointeger(L, -1), 1);
 	lua_rawgeti(L, facetbl, 3);
-	lily_assert_int_equal(lua_tointeger(L, -1), 3);
+	lily_assert_int_equal(lua_tointeger(L, -1), 2);
 	lua_rawgeti(L, facetbl, 4);
-	lily_assert_int_equal(lua_tointeger(L, -1), 4);
+	lily_assert_int_equal(lua_tointeger(L, -1), 3);
 	lua_rawgeti(L, facetbl, 5);
-	lily_assert_int_equal(lua_tointeger(L, -1), 5);
+	lily_assert_int_equal(lua_tointeger(L, -1), 4);
 	lua_rawgeti(L, facetbl, 6);
-	lily_assert_int_equal(lua_tointeger(L, -1), 6);
+	lily_assert_int_equal(lua_tointeger(L, -1), 5);
 
 	lua_close(L);
 }
@@ -414,8 +415,8 @@ static int check_face(lua_State *L, int meshtbl, const char *field, int index,
 
 void test_faces(lua_State *L, int meshtbl)
 {
-	check_face(L, meshtbl, "faces", 1, 1, 2, 4);
-	check_face(L, meshtbl, "faces", 2, 1, 4, 3);
+	check_face(L, meshtbl, "faces", 1, 0, 1, 3);
+	check_face(L, meshtbl, "faces", 2, 0, 3, 2);
 }
 
 
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