Sanitize NaN/Inf in env cubemap and tonemap to stop one-frame black flashes

shaders/envmapping.glsl

@@ -8,6 +8,14 @@ vec3 envmap_color( vec3 normal )
 	vec3 refvec = reflect(f_pos.xyz, normal); // view space
 	refvec = vec3(inv_view * vec4(refvec, 0.0)); // world space
 	vec3 envcolor = texture(envmap, refvec).rgb;
+	// Sanitize. The env cubemap can briefly contain NaN/Inf after a
+	// reflection-pass regeneration (m_empty_cubemap was bound during the
+	// face render and on NVIDIA can sample as undefined). Without this
+	// guard, a single bad texel propagates through env_reflection in
+	// apply_lights() and produces one-frame black flashes on glossy
+	// (esp. specgloss) surfaces.
+	if (any(isnan(envcolor)) || any(isinf(envcolor))) envcolor = vec3(0.0);
+	envcolor = max(envcolor, vec3(0.0));
 #else
 	vec3 envcolor = vec3(0.5);
 #endif
@@ -21,8 +29,13 @@ vec3 envmap_color_lod(vec3 fragnormal, float lod)
 #if ENVMAP_ENABLED
     vec3 refvec = reflect(f_pos.xyz, fragnormal); // view space — matches envmap_color exactly
     refvec = vec3(inv_view * vec4(refvec, 0.0));  // world space — was missing
-    return textureLod(envmap, refvec, lod).rgb;
+    vec3 envcolor = textureLod(envmap, refvec, lod).rgb;
+    // See envmap_color() above — same NaN/Inf sanitize, also needed here
+    // because mipmap generation propagates a single NaN texel across the
+    // whole mip chain.
+    if (any(isnan(envcolor)) || any(isinf(envcolor))) envcolor = vec3(0.0);
+    return max(envcolor, vec3(0.0));
 #else
     return vec3(0.5); // was vec3(0.0), match the non-LOD fallback
 #endif
-}
+}