fix(shaders): the highlight of the sun is multiplied by the cosine of its light, so surfaces no longer glare milky white under a low sun; headlights light a surface with 1.35 of its diffuse colour and add a GGX highlight of their own scaled by specgloss and param_specular instead of multiplying the whole light by one plus param_specular; normalmap, parallax, detail, shadowless, sunless and default_detail materials read param_glossiness as a Phong exponent, roughness = (2 / (n + 2))^1/4, instead of 1 - 1/n or a fixed mirror

shaders/light_common.glsl

@@ -92,6 +92,7 @@ float metalic = 0.0;
 const float AMBIENT_SCALE       = 0.65;
 const float SUN_DIFFUSE_SCALE   = 1.5;
 const float SUN_NDOTL_SHARPNESS = 1.25;
+const float HEADLIGHT_DIFFUSE_SCALE = 1.35;
 
 float length2(vec3 v)
 {
@@ -103,6 +104,13 @@ float parallax_occlusion = 0.0;
 float parallax_shadow = 0.0;
 #endif
 
+float phong_glossiness()
+{
+    float exponent = abs(param[1].w);
+    float roughness = sqrt(sqrt(2.0 / (exponent + 2.0)));
+    return (1.0 - roughness) * max(exponent, 1.0);
+}
+
 float calc_shadow()
 {
 #if SHADOWMAP_ENABLED
@@ -217,7 +225,7 @@ float G_Smith(float NdotV, float NdotL, float roughness)
 //
 //   diffuse  – Lambert N·L (Fresnel-weighted diffuse is handled per-material
 //              in apply_lights, so we return raw N·L here).
-//   specular – Cook-Torrance GGX: D·G / (4·NdotL·NdotV).
+//   specular – Cook-Torrance GGX times the cosine of the light: D·G·NdotL / (4·NdotL·NdotV).
 //              The Fresnel factor (F) is intentionally omitted here;
 //              apply_lights already carries a per-material Fresnel term
 //              that is applied to env reflections and can be routed to
@@ -244,11 +252,11 @@ vec2 calc_light(vec3 light_dir, vec3 fragnormal)
     float roughness = clamp(1.0 - glossiness / max(abs(param[1].w), 1.0), 0.04, 1.0);
 
     // Cook-Torrance specular (no Fresnel — see above):
-    //   f_spec = D(N,H,α) · G(N,V,L,α) / (4 · NdotL · NdotV)
+    //   f_spec · NdotL = D(N,H,α) · G(N,V,L,α) / (4 · NdotV)
     float D = D_GGX(NdotH, roughness);
     float G = G_Smith(NdotV, NdotL, roughness);
     float specular_v = (NdotL > 0.0)
-        ? (D * G) / max(4.0 * NdotL * NdotV, 1e-4)
+        ? (D * G) / max(4.0 * NdotV, 1e-4)
         : 0.0;
 
     return vec2(diffuse_v, specular_v);
@@ -300,7 +308,7 @@ vec2 calc_headlights(light_s light, vec3 fragnormal)
 	// Tighter wrap (was +0.25): faces angled away from the headlight cone
 	// fall off to dark much faster, so cab/exterior surfaces read with a
 	// clear directional shape instead of a flat half-lit wash.
-	vec2 part = vec2(1.0) * clamp(dot(fragnormal, light_dir) + 0.10, 0.0, 1.0);
+	vec2 part = vec2(clamp(dot(fragnormal, light_dir) + 0.10, 0.0, 1.0), calc_light(light_dir, fragnormal).y);
 	float distance = length(light.pos - f_pos.xyz);
 	float atten = 1.0f / (1.0f + light.linear * distance + light.quadratic * (distance * distance));
 	atten *= mix(1.0, 0.0, clamp((coords.z - 0.998) * 500.0, 0.0, 1.0));
@@ -420,11 +428,13 @@ vec3 apply_lights(vec3 fragcolor, vec3 fragnormal, vec3 texturecolor, float refl
     // direct sun read as too hot/burnt; raise it for more punch.
     fragcolor += lights[0].color * SUN_DIFFUSE_SCALE * (1.0 - shadow1) * diffuseamount;
 
+    vec3 headlightspecular = vec3(0.0);
     for (uint i = 1U; i < lights_count; i++)
     {
         light_s light = lights[i];
         vec2 part = calc_headlights(light, fragnormal);
-        fragcolor += light.color * (part.x + part.y * param[1].y) * light.intensity;
+        fragcolor += light.color * part.x * HEADLIGHT_DIFFUSE_SCALE * light.intensity;
+        headlightspecular += light.color * part.y * light.intensity;
     }
 
     float specularamount = sunlight.y * param[1].y * specularity * lights[0].intensity
@@ -432,7 +442,7 @@ vec3 apply_lights(vec3 fragcolor, vec3 fragnormal, vec3 texturecolor, float refl
     if (shadowtone < 1.0)
         specularamount *= clamp(1.0 - shadow1, 0.0, 1.0);
 
-    vec3 specularcolor = specularamount * lights[0].color;
+    vec3 specularcolor = specularamount * lights[0].color + headlightspecular * param[1].y * specularity;
 
     // Env reflection tracked separately — must NOT go through the albedo multiply
     // below. Gated by the pre-integrated env BRDF (env_spec) so reflection energy

shaders/mat_default_detail.frag

@@ -49,7 +49,7 @@ void main()
 	vec3 fragnormal = normalize(f_tbn * normalize(normal.xyz));
 	float reflectivity = param[1].z;
 	float specularity = (tex_color.r + tex_color.g + tex_color.b) * 0.5;
-	glossiness = abs(param[1].w);
+	glossiness = phong_glossiness();
 	
 	fragcolor = apply_lights(fragcolor, fragnormal, tex_color.rgb, reflectivity, specularity, shadow_tone);
 	vec4 color = vec4(apply_fog(fragcolor), tex_color.a * alpha_mult);

shaders/mat_detail_normalmap.frag

@@ -63,6 +63,7 @@ void main()
 	float reflectivity = reflblend > 1.0 ? param[1].z * 1.0 : param[1].z * reflblend;
 	float specularity = (tex_color.r + tex_color.g + tex_color.b) * 0.5;
 	
+	glossiness = phong_glossiness();
 	fragcolor = apply_lights(fragcolor, fragnormal, tex_color.rgb, reflectivity, specularity, shadow_tone);
 	vec4 color = vec4(apply_fog(fragcolor), tex_color.a * alpha_mult);
 #if POSTFX_ENABLED

shaders/mat_detail_parallax.frag

@@ -70,6 +70,7 @@ void main()
 	float reflectivity = param[1].z * normal_map.a;
 	float specularity = (tex_color.r + tex_color.g + tex_color.b) * 0.5;	
 	
+	glossiness = phong_glossiness();
 	fragcolor = apply_lights(fragcolor, fragnormal, tex_color.rgb, reflectivity, specularity, shadow_tone);
 
 	vec4 color = vec4(apply_fog(fragcolor), tex_color.a * alpha_mult);

shaders/mat_normalmap.frag

@@ -49,6 +49,7 @@ void main()
 	float reflectivity = param[1].z * texture(normalmap, f_coord).a;
 	float specularity = (tex_color.r + tex_color.g + tex_color.b) * 0.5;
 
+	glossiness = phong_glossiness();
 	fragcolor = apply_lights(fragcolor, fragnormal, tex_color.rgb, reflectivity, specularity, shadow_tone);
 
 	vec4 color = vec4(apply_fog(fragcolor), tex_color.a * alpha_mult);

shaders/mat_parallax.frag

@@ -57,6 +57,7 @@ void main()
 	float reflectivity = param[1].z * texture(normalmap, f_coord_p).a;
 	float specularity = (tex_color.r + tex_color.g + tex_color.b) * 0.5;	
 	
+	glossiness = phong_glossiness();
 	fragcolor = apply_lights(fragcolor, fragnormal, tex_color.rgb, reflectivity, specularity, shadow_tone);
 
 	vec4 color = vec4(apply_fog(fragcolor), tex_color.a * alpha_mult);

shaders/mat_shadowlessnormalmap.frag

@@ -48,7 +48,7 @@ void main()
 	vec3 fragnormal = normalize(f_tbn * normalize(normal.xyz));
 	float reflectivity = param[1].z * texture(normalmap, f_coord).a;
 	float specularity = (tex_color.r + tex_color.g + tex_color.b) * 0.5;
-	glossiness = abs(param[1].w);
+	glossiness = phong_glossiness();
 	
 	fragcolor = apply_lights(fragcolor, fragnormal, tex_color.rgb, reflectivity, specularity, 1.0);
 	vec4 color = vec4(apply_fog(fragcolor), tex_color.a * alpha_mult);

shaders/mat_sunlessnormalmap.frag

@@ -64,7 +64,7 @@ vec3 apply_lights_sunless(vec3 fragcolor, vec3 fragnormal, vec3 texturecolor, fl
 	float diffuseamount = sun_NdotL * lights[0].intensity;
 	fragcolor += envcolor * reflectivity;
 	float specularamount = (sunlight.y * param[1].y * specularity) * lights[0].intensity;
-	glossiness = abs(param[1].w);
+	glossiness = phong_glossiness();
 
 	for (uint i = 1U; i < lights_count; i++)
 	{