glarrays.go

package noodle

import (
	"fmt"
	"reflect"
	"runtime"
	"syscall/js"
	"unsafe"
)

// Shamelessly stolen from https://github.com/bobcob7/wasm-rotating-cube/blob/master/gltypes/arrays.go
// Shamelessly stolen from: https://github.com/golang/go/issues/32402
// Thanks hajimehoshi
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))
	case []Vector2:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4 * 2
		h.Cap *= 4 * 2
		return *(*[]byte)(unsafe.Pointer(h))
	case []Vector3:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4 * 3
		h.Cap *= 4 * 3
		return *(*[]byte)(unsafe.Pointer(h))
	case []Vector4:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4 * 4
		h.Cap *= 4 * 4
		return *(*[]byte)(unsafe.Pointer(h))
	case []Matrix:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4 * 16
		h.Cap *= 4 * 16
		return *(*[]byte)(unsafe.Pointer(h))
	default:
		panic(fmt.Sprintf("jsutil: unexpected value at sliceToBytesSlice: %T", s))
	}
}

//sliceToTypedArray converts a slice of values (a buffer) into a JavaScript equivilent typed array
func sliceToTypedArray(s interface{}) js.Value {
	switch s := s.(type) {
	case js.Value:
		return s

	//Bytes
	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"))

	//Ints
	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)

	//Floats
	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)

	//Vectors
	case []Vector2:
		a := js.Global().Get("Uint8Array").New((len(s) * 2) * 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 []Vector3:
		a := js.Global().Get("Uint8Array").New((len(s) * 3) * 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 []Vector4:
		a := js.Global().Get("Uint8Array").New((len(s) * 4) * 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)

	default:
		panic(fmt.Sprintf("jsutil: unexpected value at SliceToTypedArray: %T", s))
	}
}