qbsp: merge across liquids by default in q1

- change option name to -nomergeacrossliquids
- add docs
- allow using it in q2 as well (requested by jitspoe)

docs/qbsp.rst

@@ -40,6 +40,14 @@ Options
 
    Don't perform face merging.
 
+.. option:: -nomergeacrossliquids
+
+   Don't merge faces above and below a liquid.
+
+   This is for maps targetting ezQuake (Q1) and Paintball2 (Q2) water caustics,
+   where the effect is applied per-face and breaks if a face is partially above
+   and partially below water.
+
 .. option:: -noedgereuse
 
    Don't reuse edges (may be useful for debugging software rendering).

include/qbsp/qbsp.hh

@@ -174,7 +174,7 @@ public:
     setting_int32 subdivide;
     setting_bool nofill;
     setting_bool nomerge;
-    setting_bool mergeacrosswater;
+    setting_bool nomergeacrossliquids;
     setting_bool noedgereuse;
     setting_bool noclip;
     setting_bool noskip;

qbsp/merge.cc

@@ -72,20 +72,19 @@ static std::unique_ptr<face_t> TryMerge(const face_t *f1, const face_t *f2)
         f1->original_side->lmshift != f2->original_side->lmshift)
         return NULL;
 
-    if (qbsp_options.target_game->id != GAME_QUAKE_II) {
-        if (!qbsp_options.mergeacrosswater.value()) {
-            // Q1: don't merge across water boundaries; ezQuake/nQuake water caustics will leak onto
-            // above-water faces.
-            if (f1->contents[0].is_liquid(qbsp_options.target_game) !=
-                f2->contents[0].is_liquid(qbsp_options.target_game))
-                return nullptr;
-        }
-
-        // Q1: don't merge across sky boundary - we delete faces inside sky
-        if (f1->contents[0].is_sky(qbsp_options.target_game) != f2->contents[0].is_sky(qbsp_options.target_game))
+    if (qbsp_options.nomergeacrossliquids.value()) {
+        // if requested, block merging across water boundaries;
+        // ezQuake/nQuake (Q1) and Paintball2 (Q2) water caustics will leak onto
+        // above-water faces.
+        if (f1->contents[0].is_liquid(qbsp_options.target_game) !=
+            f2->contents[0].is_liquid(qbsp_options.target_game))
             return nullptr;
     }
 
+    // Q1: don't merge across sky boundary - we delete faces inside sky
+    if (f1->contents[0].is_sky(qbsp_options.target_game) != f2->contents[0].is_sky(qbsp_options.target_game))
+        return nullptr;
+
     // find a common edge
     p1 = p2 = NULL; // stop compiler warning
     j = 0; //

qbsp/qbsp.cc

@@ -463,7 +463,7 @@ qbsp_settings::qbsp_settings()
           "change the subdivide threshold, in luxels. 0 will disable subdivision entirely"},
       nofill{this, "nofill", false, &debugging_group, "don't perform outside filling"},
       nomerge{this, "nomerge", false, &debugging_group, "don't perform face merging"},
-      mergeacrosswater{this, "mergeacrosswater", false, &common_format_group, "merge faces that cross above and below water"},
+      nomergeacrossliquids{this, "nomergeacrossliquids", false, &common_format_group, "block merging faces that cross above and below water"},
       noedgereuse{this, "noedgereuse", false, &debugging_group, "don't reuse edges (for debugging software rendering)"},
       noclip{this, "noclip", false, &common_format_group, "don't write clip nodes (Q1-like BSP formats)"},
       noskip{this, "noskip", false, &debugging_group, "don't remove faces with the 'skip' texture"},

tests/test_qbsp.cc

@@ -2126,7 +2126,7 @@ TEST_CASE("lq e3m4.map" * doctest::may_fail())
 TEST_CASE("q1_tjunc_matrix")
 {
     // TODO: test opaque water in q1 mode
-    const auto [b, bspx, prt] = LoadTestmap("q1_tjunc_matrix.map", {"-mergeacrosswater"});
+    const auto [b, bspx, prt] = LoadTestmap("q1_tjunc_matrix.map");
     const mbsp_t &bsp = b; // workaround clang not allowing capturing bindings in lambdas
     auto *game = bsp.loadversion->game;
 
@@ -2175,7 +2175,6 @@ TEST_CASE("q1_tjunc_matrix")
         CHECK(!has_tjunc(INDEX_SOLID, INDEX_DETAIL_FENCE_MIRRORINSIDE));
         CHECK(!has_tjunc(INDEX_SOLID, INDEX_DETAIL_ILLUSIONARY));
         CHECK(!has_tjunc(INDEX_SOLID, INDEX_DETAIL_ILLUSIONARY_NOCLIPFACES));
-        // "-mergeacrosswater" is needed to prevent a weld between transparent water and solid
         CHECK(!has_tjunc(INDEX_SOLID, INDEX_WATER));
         CHECK( has_tjunc(INDEX_SOLID, INDEX_SKY));
     }