add wgpu.BytesToJS helper function

wgpu/adapt_js.go

@@ -37,6 +37,16 @@ func ensureBufferSize(size int) {
 	uint8Array = js.Global().Get("Uint8Array").New(arrayBuffer)
 }
 
+// BytesToJS converts the given bytes to a js Uint8Array
+// by using the global wasm memory bytes. This avoids the
+// copying present in [js.CopyBytesToJS].
+func BytesToJS(b []byte) js.Value {
+	ptr := uintptr(unsafe.Pointer(&b[0]))
+	memoryBytes := js.Global().Get("Uint8Array").New(js.Global().Get("wasm").Get("instance").Get("exports").Get("mem").Get("buffer"))
+	// using subarray instead of slice gives a 5x performance improvement due to no copying
+	return memoryBytes.Call("subarray", ptr, ptr+uintptr(len(b)))
+}
+
 // DataTypes represents allowed data slice types.
 type DataTypes interface {
 	~int8 | ~uint8 | ~int16 | ~uint16 | ~int32 | ~uint32 | ~float32 | ~float64