feat: 材质系统 v1——4 纹理槽（albedo/normal/specular/emissive）+ 法线贴图

- Material：单贴图 → 4 槽（binding=Slot 枚举），MakeCacheKey 组合键
  保持材质去重（同贴图组合共享描述符集）
- Model：读取 aiTextureType DIFFUSE/NORMALS/SPECULAR/EMISSIVE 四类路径；
  aiProcess_CalcTangentSpace 生成切线（Vertex +tangent 属性，location 3）；
  每槽默认纹理兜底（白/平法线(128,128,255)/黑/黑，1x1）
- 纹理 sRGB 语义按槽位：颜色图 SRGB 变体，数据图（Normal/Specular）线性
  UNORM——Texture 路径加载加 srgb 参数；修复 InitFromPixels 图文 format
  不一致的 validation 警告
- UBO 尾部追加 cameraPos（Blinn-Phong V 向量）
- simple_shader.frag：TBN 法线贴图（无切线/平法线退化回几何法线）+
  Blinn-Phong 高光（specular 图强度系数）+ 自发光直加
- SunTemple 实测：148 张 DDS 全槽位加载（96 张线性变体）、1056 mesh、
  validation 零警告

shaders/simple_shader.frag

@@ -12,6 +12,7 @@ layout(location = 1) in vec3 fragNormal;
 layout(location = 2) in vec3 fragWorldPos;
 layout(location = 3) in float fragViewDepth;
 layout(location = 4) in vec2 fragVelocity;
+layout(location = 5) in vec3 fragTangent;
 
 layout(location = 0) out vec4 outColor;
 layout(location = 1) out vec2 outVelocity;   // TAA velocity 附件
@@ -26,9 +27,15 @@ layout(set = 0, binding = 0) uniform UniformBufferObject {
     mat4 projNoJitter;
     mat4 prevView;
     mat4 prevProj;
+    vec4 cameraPos;
 } ubo;
 
-layout(set = 1, binding = 0) uniform sampler2D texSampler;
+// 材质纹理槽（binding = Material::Slot）
+layout(set = 1, binding = 0) uniform sampler2D albedoMap;
+layout(set = 1, binding = 1) uniform sampler2D normalMap;
+layout(set = 1, binding = 2) uniform sampler2D specularMap;
+layout(set = 1, binding = 3) uniform sampler2D emissiveMap;
+
 layout(set = 2, binding = 0) uniform sampler2D shadowMap0;   // CSM 级联 0（最近）
 layout(set = 2, binding = 1) uniform sampler2D shadowMap1;   // 级联 1
 layout(set = 2, binding = 2) uniform sampler2D shadowMap2;   // 级联 2（最远）
@@ -60,19 +67,45 @@ float ShadowFactor(vec3 N, float viewDepth) {
     return (proj.z - bias > closest) ? 0.3 : 1.0;
 }
 
+// 法线贴图 → 世界空间法线（TBN 构建）。
+// 无切线数据（零向量）或平法线贴图时退回几何法线。
+vec3 MappedNormal(vec3 geomN, vec3 T, vec2 uv) {
+    if (dot(T, T) < 1e-4) return geomN;
+
+    vec3 N = geomN;
+    vec3 nT = normalize(T - N * dot(N, T));   // 正交化
+    vec3 B = cross(N, nT);
+    vec3 sampled = texture(normalMap, uv).xyz * 2.0 - 1.0;
+    if (dot(sampled, sampled) < 1e-4) return geomN;
+
+    return normalize(nT * sampled.x + B * sampled.y + N * sampled.z);
+}
+
 void main() {
-    vec3 albedo = texture(texSampler, fragUV).rgb;
-    vec3 N = normalize(fragNormal);
+    vec3 albedo = texture(albedoMap, fragUV).rgb;
+    float specIntensity = texture(specularMap, fragUV).r;
+    vec3 emissive = texture(emissiveMap, fragUV).rgb;
+
+    vec3 N = MappedNormal(normalize(fragNormal), fragTangent, fragUV);
+    vec3 V = normalize(ubo.cameraPos.xyz - fragWorldPos);
 
     vec3 result = ubo.ambientColor.rgb * albedo;
 
     for (int i = 0; i < MAX_LIGHTS; ++i) {
         vec3 L = normalize(-ubo.lights[i].direction.xyz);
         float diff = max(dot(N, L), 0.0);
+        // Blinn-Phong 高光（半程向量；specular 图做强度系数）
+        vec3 H = normalize(L + V);
+        float spec = pow(max(dot(N, H), 0.0), 32.0) * specIntensity;
+
         float shade = (i == 0) ? ShadowFactor(N, fragViewDepth) : 1.0;
-        result += ubo.lights[i].color.rgb * ubo.lights[i].color.a * diff * albedo * shade;
+        result += ubo.lights[i].color.rgb * ubo.lights[i].color.a *
+                  (albedo * diff + vec3(spec)) * shade;
     }
 
+    // 自发光不经光照/阴影直接叠加
+    result += emissive;
+
     outColor = vec4(result, 1.0);
     outVelocity = fragVelocity;
 }