light: fix lightgrid assertion failure if lightgrid gets a nan (separate bug)

include/light/ltface.hh

@@ -67,6 +67,10 @@ struct lightgrid_sample_t
     qvec3b round_to_int() const;
     float brightness() const;
 
+    /**
+     * - if !used, style and color are ignored for equality
+     * - if a color component is nan, nan is considered equal to nan for the purposes of this comparison
+     */
     bool operator==(const lightgrid_sample_t &other) const;
 };
 

light/ltface.cc

@@ -3555,7 +3555,29 @@ float lightgrid_sample_t::brightness() const
 
 bool lightgrid_sample_t::operator==(const lightgrid_sample_t &other) const
 {
-    return used == other.used && style == other.style && color == other.color;
+    if (used != other.used)
+        return false;
+
+    if (!used) {
+        // if unused, style and color don't matter
+        return true;
+    }
+
+    if (style != other.style)
+        return false;
+
+    // color check requires special handling for nan
+    for (int i=0; i<3; ++i) {
+        if (std::isnan(color[i])) {
+            if (!std::isnan(other.color[i]))
+                return false;
+        } else {
+            if (color[i] != other.color[i])
+                return false;
+        }
+    }
+
+    return true;
 }
 
 int lightgrid_samples_t::used_styles() const

tests/test_ltface.cc

@@ -1,6 +1,7 @@
 #include <doctest/doctest.h>
 
 #include <light/light.hh>
+#include <light/ltface.hh>
 #include <light/surflight.hh>
 #include <common/bspinfo.hh>
 #include <qbsp/qbsp.hh>
@@ -103,6 +104,48 @@ testresults_t QbspVisLight_Q2(
     return QbspVisLight_Common(name, {"-q2bsp"}, extra_light_args, run_vis);
 }
 
+TEST_CASE("lightgrid_sample_t equality")
+{
+    SUBCASE("style equality") {
+        lightgrid_sample_t a {.used = true, .style = 4, .color = {}};
+        lightgrid_sample_t b = a;
+        CHECK(a == b);
+
+        b.style = 6;
+        CHECK(a != b);
+    }
+
+    SUBCASE("color equality") {
+        lightgrid_sample_t a {.used = true, .style = 4, .color = {1,2,3}};
+        lightgrid_sample_t b = a;
+        CHECK(a == b);
+
+        b.color = {6,5,4};
+        CHECK(a != b);
+    }
+
+    SUBCASE("nan colors") {
+        lightgrid_sample_t a {.used = true, .style = 4, .color = {std::numeric_limits<double>::quiet_NaN(), 1.0, 1.0}};
+        lightgrid_sample_t b = a;
+        CHECK(a == b);
+
+        b.color = { 0,0,0};
+        CHECK(a != b);
+    }
+
+    SUBCASE("unused equality doesn't consider other attributes") {
+        lightgrid_sample_t a, b;
+        CHECK(!a.used);
+        CHECK(a == b);
+
+        b.style = 5;
+        CHECK(a == b);
+
+        b.color = {1, 0, 0};
+        CHECK(a == b);
+    }
+}
+
 TEST_CASE("-world_units_per_luxel, -lightgrid")
 {
     auto [bsp, bspx] = QbspVisLight_Q2("q2_lightmap_custom_scale.map", {"-lightgrid"});