Restore allowance of unaligned buffer-texture copies

This fixes a regression introduced by gfx-rs#7948. However, it makes it
possible to reach a panic in initialize_buffer_memory if the copy
requires initializing a region of memory that is not 4B aligned.

Author: andyleiserson

cts_runner/test.lst

@@ -1,6 +1,7 @@
 unittests:*
 webgpu:api,operation,command_buffer,basic:*
 webgpu:api,operation,command_buffer,copyBufferToBuffer:*
+webgpu:api,operation,command_buffer,image_copy:offsets_and_sizes:*
 webgpu:api,operation,compute,basic:memcpy:*
 //FAIL: webgpu:api,operation,compute,basic:large_dispatch:*
 webgpu:api,operation,compute_pipeline,overrides:*
@@ -63,6 +64,7 @@ fails-if(dx12) webgpu:api,validation,image_copy,buffer_texture_copies:offset_and
 //mix of PASS and FAIL: other subtests of offset_and_bytesPerRow. Related bugs:
 // https://github.com/gfx-rs/wgpu/issues/7946, https://github.com/gfx-rs/wgpu/issues/7947
 webgpu:api,validation,image_copy,layout_related:copy_end_overflows_u64:*
+webgpu:api,validation,image_copy,layout_related:offset_alignment:*
 webgpu:api,validation,image_copy,texture_related:format:dimension="1d";*
 webgpu:api,validation,queue,submit:command_buffer,device_mismatch:*
 webgpu:api,validation,queue,submit:command_buffer,duplicate_buffers:*
@@ -92,6 +94,7 @@ webgpu:api,validation,encoding,queries,general:occlusion_query,query_type:*
 webgpu:shader,execution,expression,call,builtin,textureSample:sampled_1d_coords:*
 webgpu:shader,execution,expression,call,builtin,textureSampleBaseClampToEdge:2d_coords:stage="c";textureType="texture_2d<f32>";*
 webgpu:shader,execution,flow_control,return:*
+webgpu:shader,execution,robust_access_vertex:vertex_buffer_access:*
 webgpu:shader,validation,expression,call,builtin,max:values:*
 webgpu:shader,validation,statement,statement_behavior:invalid_statements:body="break"
 webgpu:shader,validation,statement,statement_behavior:invalid_statements:body="break_if"

wgpu-core/src/command/transfer.rs

@@ -399,7 +399,7 @@ pub(crate) fn validate_texture_buffer_copy<T>(
         return Err(TransferError::CopyAspectNotOne);
     }
 
-    let mut offset_alignment = if desc.format.is_depth_stencil_format() {
+    let offset_alignment = if desc.format.is_depth_stencil_format() {
         4
     } else {
         // The case where `block_copy_size` returns `None` is currently
@@ -411,17 +411,7 @@ pub(crate) fn validate_texture_buffer_copy<T>(
             .expect("non-copyable formats should have been rejected previously")
     };
 
-    // TODO(https://github.com/gfx-rs/wgpu/issues/7947): This does not match the spec.
-    // The spec imposes no alignment requirement if `!aligned`, and otherwise
-    // imposes only the `offset_alignment` as calculated above. wgpu currently
-    // can panic on alignments <4B, so we reject them here to avoid a panic.
-    if aligned {
-        offset_alignment = offset_alignment.max(4);
-    } else {
-        offset_alignment = 4;
-    }
-
-    if offset % u64::from(offset_alignment) != 0 {
+    if aligned && offset % u64::from(offset_alignment) != 0 {
         return Err(TransferError::UnalignedBufferOffset(offset));
     }