Fix WebGL context attribute handling for enableExtensionsByDefault and explicitSwapControl, and work around Chrome behavior that it does not return powerPreference in context attributes. (#7996)

Author: juj

src/library_gl.js

@@ -767,7 +767,7 @@ var LibraryGL = {
     registerContext: function(ctx, webGLContextAttributes) {
       var handle = _malloc(8); // Make space on the heap to store GL context attributes that need to be accessible as shared between threads.
 #if GL_SUPPORT_EXPLICIT_SWAP_CONTROL
-      {{{ makeSetValue('handle', 0, 'webGLContextAttributes["explicitSwapControl"]', 'i32')}}}; // explicitSwapControl
+      {{{ makeSetValue('handle', 0, 'webGLContextAttributes.explicitSwapControl', 'i32')}}}; // explicitSwapControl
 #endif
 #if USE_PTHREADS
       {{{ makeSetValue('handle', 4, '_pthread_self()', 'i32')}}}; // the thread pointer of the thread that owns the control of the context

src/library_html5.js

@@ -2361,16 +2361,16 @@ var LibraryJSEvents = {
     {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.antialias, 't.antialias', 'i32') }}};
     {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.premultipliedAlpha, 't.premultipliedAlpha', 'i32') }}};
     {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.preserveDrawingBuffer, 't.preserveDrawingBuffer', 'i32') }}};
-    var power = __emscripten_webgl_power_preferences.indexOf(t['powerPreference']);
+    var power = t['powerPreference'] && __emscripten_webgl_power_preferences.indexOf(t['powerPreference']);
     {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.powerPreference, 'power', 'i32') }}};
     {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.failIfMajorPerformanceCaveat, 't.failIfMajorPerformanceCaveat', 'i32') }}};
     {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.majorVersion, 'c.version', 'i32') }}};
     {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.minorVersion, 0, 'i32') }}};
 #if GL_SUPPORT_AUTOMATIC_ENABLE_EXTENSIONS
-    {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.enableExtensionsByDefault, 'c.attributes["enableExtensionsByDefault"]', 'i32') }}};
+    {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.enableExtensionsByDefault, 'c.attributes.enableExtensionsByDefault', 'i32') }}};
 #endif
 #if GL_SUPPORT_EXPLICIT_SWAP_CONTROL
-    {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.explicitSwapControl, 'c.attributes["explicitSwapControl"]', 'i32') }}};
+    {{{ makeSetValue('a', C_STRUCTS.EmscriptenWebGLContextAttributes.explicitSwapControl, 'c.attributes.explicitSwapControl', 'i32') }}};
 #endif
     return {{{ cDefine('EMSCRIPTEN_RESULT_SUCCESS') }}};
   },