Merge branch 'master' into stencilMask

* master:
  Move GL_CHECK to GL callsites.
  make sure depth textures are resolved as well when blitting frameBuffer
  Cleanup.
  Adjust integer texture format enums for desktop OpenGL < 4.0
  Revert back to using GL_HALF_FLOAT (that is GL_HALF_FLOAT_OES)
  Fix OpenGL ES texture formats and remove runtime texture probing on WebGL.
  Cleanup.
  Create WebGL 2 context if available. Work around Chrome performance bug https://bugs.chromium.org/p/chromium/issues/detail?id=1045643
  Optimize glUniform1iv and glUniform4fv to use faster glUniform1i and glUniform4f on WebGL.
  Avoid redundant GL calls to glEnableVertexAttribArray() and glDisableVertexAttribArray(). bkaradzic#1960

src/glcontext_html5.cpp

@@ -108,37 +108,35 @@ namespace bgfx { namespace gl
 	{
 		emscripten_webgl_init_context_attributes(&s_attrs);
 
-		s_attrs.alpha = false;
+		// Work around bug https://bugs.chromium.org/p/chromium/issues/detail?id=1045643 in Chrome
+		// by having alpha always enabled.
+		s_attrs.alpha = true;
+		s_attrs.premultipliedAlpha = false;
 		s_attrs.depth = true;
 		s_attrs.stencil = true;
 		s_attrs.enableExtensionsByDefault = true;
+		s_attrs.antialias = false;
 
-		// let emscripten figure out the best WebGL context to create
-		s_attrs.majorVersion = 0;
-		s_attrs.majorVersion = 0;
-
+		s_attrs.minorVersion = 0;
 		const char* canvas = (const char*) _nwh;
 
-		int context = emscripten_webgl_create_context(canvas, &s_attrs);
-
-		if (context <= 0)
-		{
-			BX_TRACE("Failed to create WebGL context.  (Canvas handle: '%s', error %d)", canvas, (int)context);
-			return NULL;
-		}
-
-		int result = emscripten_webgl_make_context_current(context);
-		if (EMSCRIPTEN_RESULT_SUCCESS != result)
+		for(int version = 2; version >= 1; --version)
 		{
-			BX_TRACE("emscripten_webgl_make_context_current failed (%d)", result);
-			return NULL;
-		}
+			s_attrs.majorVersion = version;
+			EMSCRIPTEN_WEBGL_CONTEXT_HANDLE context = emscripten_webgl_create_context(canvas, &s_attrs);
+			if (context > 0)
+			{
+				emscripten_webgl_make_context_current(context);
 
-		SwapChainGL* swapChain = BX_NEW(g_allocator, SwapChainGL)(context, canvas);
+				SwapChainGL* swapChain = BX_NEW(g_allocator, SwapChainGL)(context, canvas);
 
-		import(1);
+				import(1);
 
-		return swapChain;
+				return swapChain;
+			}
+		}
+		BX_TRACE("Failed to create WebGL context.  (Canvas handle: '%s', error %d)", canvas, (int)context);
+		return NULL;
 	}
 
 	uint64_t GlContext::getCaps() const