From 6fe6543b4b649a96c9e8bdd24b3644b0c3acc80c Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Tue, 6 Apr 2021 00:09:50 +0900
Subject: [PATCH] internal/graphicsdriver/opengl: Bug fix: getBufferSubData was
 available only with WebGL2

---
 internal/graphicsdriver/opengl/context_js.go | 10 +++++-----
 internal/graphicsdriver/opengl/gl_js.go      |  5 +++--
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/internal/graphicsdriver/opengl/context_js.go b/internal/graphicsdriver/opengl/context_js.go
index b2904e8b0..4ec284e30 100644
--- a/internal/graphicsdriver/opengl/context_js.go
+++ b/internal/graphicsdriver/opengl/context_js.go
@@ -587,15 +587,15 @@ func (c *context) replacePixelsWithPBO(buffer buffer, t textureNative, width, he
 }
 
 func (c *context) getBufferSubData(buffer buffer, width, height int) []byte {
+	if !isWebGL2Available {
+		panic("opengl: WebGL2 must be available when getBufferSubData is called")
+	}
+
 	gl := c.gl
 	gl.bindBuffer.Invoke(gles.PIXEL_UNPACK_BUFFER, js.Value(buffer))
 	l := 4 * width * height
 	arr := jsutil.TemporaryUint8Array(l, nil)
-	if isWebGL2Available {
-		gl.getBufferSubData.Invoke(gles.PIXEL_UNPACK_BUFFER, 0, arr, 0, l)
-	} else {
-		gl.getBufferSubData.Invoke(gles.PIXEL_UNPACK_BUFFER, 0, arr.Call("subarray", 0, l))
-	}
+	gl.getBufferSubData.Invoke(gles.PIXEL_UNPACK_BUFFER, 0, arr, 0, l)
 	gl.bindBuffer.Invoke(gles.PIXEL_UNPACK_BUFFER, nil)
 	return jsutil.Uint8ArrayToSlice(arr, l)
 }
diff --git a/internal/graphicsdriver/opengl/gl_js.go b/internal/graphicsdriver/opengl/gl_js.go
index 5cd08d37f..7fb73103a 100644
--- a/internal/graphicsdriver/opengl/gl_js.go
+++ b/internal/graphicsdriver/opengl/gl_js.go
@@ -112,7 +112,6 @@ func newGL(v js.Value) *gl {
 		enableVertexAttribArray:  v.Get("enableVertexAttribArray").Call("bind", v),
 		framebufferTexture2D:     v.Get("framebufferTexture2D").Call("bind", v),
 		flush:                    v.Get("flush").Call("bind", v),
-		getBufferSubData:         v.Get("getBufferSubData").Call("bind", v),
 		getParameter:             v.Get("getParameter").Call("bind", v),
 		getProgramInfoLog:        v.Get("getProgramInfoLog").Call("bind", v),
 		getProgramParameter:      v.Get("getProgramParameter").Call("bind", v),
@@ -145,7 +144,9 @@ func newGL(v js.Value) *gl {
 		vertexAttribPointer:      v.Get("vertexAttribPointer").Call("bind", v),
 		viewport:                 v.Get("viewport").Call("bind", v),
 	}
-	if !isWebGL2Available {
+	if isWebGL2Available {
+		g.getExtension = v.Get("getBufferSubData").Call("bind", v)
+	} else {
 		g.getExtension = v.Get("getExtension").Call("bind", v)
 	}
 	return g