supported uint8_index_type

inc/hgl/graph/VK.h

@@ -138,8 +138,9 @@ inline const uint32_t GetMipLevel(const VkExtent3D &ext)
 /**
  * 索引类型,等同于VkIndexType
  */
-enum IndexType:uint
+enum IndexType:int
 {
+    AUTO=-1,
     U16=0,
     U32,
     U8=VK_INDEX_TYPE_UINT8_EXT,
@@ -147,6 +148,11 @@ enum IndexType:uint
     ERR=VK_INDEX_TYPE_MAX_ENUM
 };
 
+inline const bool IsIndexType(const IndexType it)
+{
+    return it>=U16&&it<=U8;
+}
+
 //Push Constant max-lengths:
 //
 //    256 bytes:  nvidia,arm