From e012c3f393792cc6a3b75547c04aacbd09e2c0b0 Mon Sep 17 00:00:00 2001
From: Elias Naur <mail@eliasnaur.com>
Date: Thu, 31 Dec 2020 12:26:08 +0100
Subject: [PATCH] internal/glimpl: [wasm] pass correctly sized buffers to WebGL
 functions

Before this change, the entire byte buffer would be passed to WebGL, even
though its size may be (much) larger than the source data.
Remakably, this hasn't resulted in any problems until the use of
glBufferSubData, which require the passed data fits the buffer size.

As a bonus, this fix should speed up the wasm port by virtue of passing
much less data across the wasm<->js barrier.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
---
 internal/glimpl/gl_js.go | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/internal/glimpl/gl_js.go b/internal/glimpl/gl_js.go
index ba862d06..38c2dac4 100644
--- a/internal/glimpl/gl_js.go
+++ b/internal/glimpl/gl_js.go
@@ -13,15 +13,21 @@ type Functions struct {
 	EXT_disjoint_timer_query        js.Value
 	EXT_disjoint_timer_query_webgl2 js.Value
 
+	// Cached reference to the Uint8Array JS type.
+	uint8Array js.Value
+
 	// Cached JS arrays.
-	byteBuf  js.Value
+	arrayBuf js.Value
 	int32Buf js.Value
 }
 
 type Context js.Value
 
 func NewFunctions(ctx Context) (*Functions, error) {
-	f := &Functions{Ctx: js.Value(ctx)}
+	f := &Functions{
+		Ctx:        js.Value(ctx),
+		uint8Array: js.Global().Get("Uint8Array"),
+	}
 	if err := f.Init(); err != nil {
 		return nil, err
 	}
@@ -268,9 +274,9 @@ func (f *Functions) RenderbufferStorage(target, internalformat Enum, width, heig
 	f.Ctx.Call("renderbufferStorage", int(target), int(internalformat), width, height)
 }
 func (f *Functions) ReadPixels(x, y, width, height int, format, ty Enum, data []byte) {
-	f.resizeByteBuffer(len(data))
-	f.Ctx.Call("readPixels", x, y, width, height, int(format), int(ty), f.byteBuf)
-	js.CopyBytesToGo(data, f.byteBuf)
+	ba := f.byteArrayOf(data)
+	f.Ctx.Call("readPixels", x, y, width, height, int(format), int(ty), ba)
+	js.CopyBytesToGo(data, ba)
 }
 func (f *Functions) Scissor(x, y, width, height int32) {
 	f.Ctx.Call("scissor", x, y, width, height)
@@ -320,18 +326,19 @@ func (f *Functions) byteArrayOf(data []byte) js.Value {
 		return js.Null()
 	}
 	f.resizeByteBuffer(len(data))
-	js.CopyBytesToJS(f.byteBuf, data)
-	return f.byteBuf
+	ba := f.uint8Array.New(f.arrayBuf, int(0), int(len(data)))
+	js.CopyBytesToJS(ba, data)
+	return ba
 }
 
 func (f *Functions) resizeByteBuffer(n int) {
 	if n == 0 {
 		return
 	}
-	if !f.byteBuf.IsUndefined() && f.byteBuf.Length() >= n {
+	if !f.arrayBuf.IsUndefined() && f.arrayBuf.Length() >= n {
 		return
 	}
-	f.byteBuf = js.Global().Get("Uint8Array").New(n)
+	f.arrayBuf = js.Global().Get("ArrayBuffer").New(n)
 }
 
 func paramVal(v js.Value) int {