added downlevel restriction error message for InvalidFormatUsages error

wgpu-core/src/device/mod.rs

@@ -800,9 +800,17 @@ impl<A: HalApi> Device<A> {
 
         let missing_allowed_usages = desc.usage - format_features.allowed_usages;
         if !missing_allowed_usages.is_empty() {
+            // detect downlevel incompatibilities
+            let wgpu_allowed_usages = desc
+                .format
+                .describe()
+                .guaranteed_format_features
+                .allowed_usages;
+            let wgpu_missing_usages = desc.usage - wgpu_allowed_usages;
             return Err(CreateTextureError::InvalidFormatUsages(
                 missing_allowed_usages,
                 desc.format,
+                wgpu_missing_usages.is_empty(),
             ));
         }
 

wgpu-core/src/resource.rs

@@ -423,8 +423,11 @@ pub enum CreateTextureError {
         "Texture descriptor mip level count {requested} is invalid, maximum allowed is {maximum}"
     )]
     InvalidMipLevelCount { requested: u32, maximum: u32 },
-    #[error("Texture usages {0:?} are not allowed on a texture of type {1:?}")]
-    InvalidFormatUsages(wgt::TextureUsages, wgt::TextureFormat),
+    #[error(
+        "Texture usages {0:?} are not allowed on a texture of type {1:?}{}",
+        if *.2 { " due to downlevel restrictions" } else { "" }
+    )]
+    InvalidFormatUsages(wgt::TextureUsages, wgt::TextureFormat, bool),
     #[error("Texture usages {0:?} are not allowed on a texture of dimensions {1:?}")]
     InvalidDimensionUsages(wgt::TextureUsages, wgt::TextureDimension),
     #[error("Texture usage STORAGE_BINDING is not allowed for multisampled textures")]