syscall/js: request: want to convert slices from/to TypedArray directly #32402
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hajimehoshi
changed the title
agnivade
added
arch-wasm
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A possible workaround, for now, is to cast slices with |
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@dennwc Thanks. Now I've succeeded to do what I wanted: func sliceToByteSlice(s interface{}) []byte {
switch s := s.(type) {
case []int8:
h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
return *(*[]byte)(unsafe.Pointer(h))
case []int16:
h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
h.Len *= 2
h.Cap *= 2
return *(*[]byte)(unsafe.Pointer(h))
case []int32:
h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
h.Len *= 4
h.Cap *= 4
return *(*[]byte)(unsafe.Pointer(h))
case []int64:
h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
h.Len *= 8
h.Cap *= 8
return *(*[]byte)(unsafe.Pointer(h))
case []uint8:
return s
case []uint16:
h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
h.Len *= 2
h.Cap *= 2
return *(*[]byte)(unsafe.Pointer(h))
case []uint32:
h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
h.Len *= 4
h.Cap *= 4
return *(*[]byte)(unsafe.Pointer(h))
case []uint64:
h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
h.Len *= 8
h.Cap *= 8
return *(*[]byte)(unsafe.Pointer(h))
case []float32:
h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
h.Len *= 4
h.Cap *= 4
return *(*[]byte)(unsafe.Pointer(h))
case []float64:
h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
h.Len *= 8
h.Cap *= 8
return *(*[]byte)(unsafe.Pointer(h))
default:
panic(fmt.Sprintf("jsutil: unexpected value at sliceToBytesSlice: %T", s))
}
}
func SliceToTypedArray(s interface{}) js.Value {
switch s := s.(type) {
case []int8:
a := js.Global().Get("Uint8Array").New(len(s))
js.CopyBytesToJS(a, sliceToByteSlice(s))
runtime.KeepAlive(s)
buf := a.Get("buffer")
return js.Global().Get("Int8Array").New(buf, a.Get("byteOffset"), a.Get("byteLength"))
case []int16:
a := js.Global().Get("Uint8Array").New(len(s) * 2)
js.CopyBytesToJS(a, sliceToByteSlice(s))
runtime.KeepAlive(s)
buf := a.Get("buffer")
return js.Global().Get("Int16Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/2)
case []int32:
a := js.Global().Get("Uint8Array").New(len(s) * 4)
js.CopyBytesToJS(a, sliceToByteSlice(s))
runtime.KeepAlive(s)
buf := a.Get("buffer")
return js.Global().Get("Int32Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/4)
case []uint8:
a := js.Global().Get("Uint8Array").New(len(s))
js.CopyBytesToJS(a, s)
runtime.KeepAlive(s)
return a
case []uint16:
a := js.Global().Get("Uint8Array").New(len(s) * 2)
js.CopyBytesToJS(a, sliceToByteSlice(s))
runtime.KeepAlive(s)
buf := a.Get("buffer")
return js.Global().Get("Uint16Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/2)
case []uint32:
a := js.Global().Get("Uint8Array").New(len(s) * 4)
js.CopyBytesToJS(a, sliceToByteSlice(s))
runtime.KeepAlive(s)
buf := a.Get("buffer")
return js.Global().Get("Uint32Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/4)
case []float32:
a := js.Global().Get("Uint8Array").New(len(s) * 4)
js.CopyBytesToJS(a, sliceToByteSlice(s))
runtime.KeepAlive(s)
buf := a.Get("buffer")
return js.Global().Get("Float32Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/4)
case []float64:
a := js.Global().Get("Uint8Array").New(len(s) * 8)
js.CopyBytesToJS(a, sliceToByteSlice(s))
runtime.KeepAlive(s)
buf := a.Get("buffer")
return js.Global().Get("Float64Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/8)
default:
panic(fmt.Sprintf("jsutil: unexpected value at SliceToTypedArray: %T", s))
}
} |
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@hajimehoshi Is this available as a library somewhere? |
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No so far. Ebiten has an internal package though: https://github.com/hajimehoshi/ebiten/tree/master/internal/jsutil |
Directly copied @hajimehoshi's workaround code from: golang/go#32402 (comment) No idea if it'll work with TinyGo wasm yet, as it uses reflect.
Using information found in comment in golang/go#32402
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I resorted to patching These methods get called quite often in my WebGL game and I can't afford indirection or extra syscalls used here: Looking for something similar to be included in the standard syscall/js library (supporting all other typed arrays too, not just Float32 which I am currently restricting myself to). An API like |
Using information found in comment in golang/go#32402
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@finnbear For performance critical code you probably want to reuse a single buffer anyways. So first create a |
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@hajimehoshi @finnbear Are you both happy with what is already possible? Shall we close this issue? |
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@neelance I'm fine with CopyBytesToJS as-is, mostly because the option to use multiple typed arrays referencing the same buffer is available. I highly suggest you document that, although I'm still using the hack I showed above because my application commonly copies float32s and bytes. I'm fine with this issue being closed 👍 |
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I'm fine with closing this issue. |
* where TypedArrayOf was removed & replaced with other techniques * the conversion was inspired & copied from issue golang/go#32402
* where TypedArrayOf was removed & replaced with other techniques * the conversion was inspired & copied from issue golang/go#32402
As
TypedArrayno longer exists as of Go 1.13, there is no way to convert slices other than[]bytefrom/to TypedArray objects other thanUint8Array. It is technically possible to do this by usingencoding/binary, but I'm worried this conversion is not efficient.As there are Web APIs that take such TypedArray objects (e.g.,
AudioBuffer.copyToChanneltakes aFloat32Array[1]), it would be very useful ifsyscall/jshad such conversion functions.CC @neelance
[1] https://developer.mozilla.org/en-US/docs/Web/API/AudioBuffer/copyToChannel
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