Add glass pipeline for WMO windows with Fresnel-based transparency

Dedicated Vulkan pipeline with alpha blending AND depth writes so
windows look transparent at oblique angles without see-through artifacts.
Fresnel alpha ranges from 0.4 (grazing) to 0.95 (head-on) with sun
glint, reflections, and silver-lining specular.

assets/shaders/wmo.frag.glsl

@@ -21,6 +21,7 @@ layout(set = 1, binding = 1) uniform WMOMaterial {
     int unlit;
     int isInterior;
     float specularIntensity;
+    int isWindow;
 };
 
 layout(set = 0, binding = 1) uniform sampler2DShadow uShadowMap;
@@ -78,5 +79,44 @@ void main() {
     float fogFactor = clamp((fogParams.y - dist) / (fogParams.y - fogParams.x), 0.0, 1.0);
     result = mix(fogColor.rgb, result, fogFactor);
 
-    outColor = vec4(result, texColor.a);
+    float alpha = texColor.a;
+
+    // Window glass: opaque but simulates dark tinted glass with reflections.
+    // No real alpha blending — we darken the base texture and add reflection
+    // on top so it reads as glass without needing the transparent pipeline.
+    if (isWindow != 0) {
+        vec3 viewDir = normalize(viewPos.xyz - FragPos);
+        float NdotV = abs(dot(norm, viewDir));
+        // Fresnel: strong reflection at grazing angles
+        float fresnel = 0.08 + 0.92 * pow(1.0 - NdotV, 4.0);
+
+        // Glass darkness depends on view angle — bright when sun glints off,
+        // darker when looking straight on with no sun reflection.
+        vec3 ldir = normalize(-lightDir.xyz);
+        vec3 reflectDir = reflect(-viewDir, norm);
+        float sunGlint = pow(max(dot(reflectDir, ldir), 0.0), 32.0);
+
+        // Base ranges from dark (0.3) to bright (0.9) based on sun reflection
+        float baseBrightness = mix(0.3, 0.9, sunGlint);
+        vec3 glass = result * baseBrightness;
+
+        // Reflection: blend sky/ambient color based on Fresnel
+        vec3 reflectTint = mix(ambientColor.rgb * 1.2, vec3(0.6, 0.75, 1.0), 0.6);
+        glass = mix(glass, reflectTint, fresnel * 0.8);
+
+        // Sharp sun glint on glass
+        vec3 halfDir = normalize(ldir + viewDir);
+        float spec = pow(max(dot(norm, halfDir), 0.0), 256.0);
+        glass += spec * lightColor.rgb * 0.8;
+
+        // Broad warm sheen when sun is nearby
+        float specBroad = pow(max(dot(norm, halfDir), 0.0), 12.0);
+        glass += specBroad * lightColor.rgb * 0.12;
+
+        result = glass;
+        // Fresnel-based transparency: more transparent at oblique angles
+        alpha = mix(0.4, 0.95, NdotV);
+    }
+
+    outColor = vec4(result, alpha);
 }