Remove support for WebGL 2 in Chrome 57 due to its high maintenance burden on code size. Reduces -15.9% of code size (997 bytes) in https://github.com/juj/webgl_render_test for WebGL 2. Introduce new setting -s OLDEST_SUPPORTED_CHROME_VERSION=x to enable customizing which Chrome versions to target.

Author: juj

src/library_webgl.js

@@ -472,6 +472,18 @@ var LibraryGL = {
       webGLContextAttributes['preserveDrawingBuffer'] = true;
 #endif
 
+#if USE_WEBGL2 && OLDEST_SUPPORTED_CHROME_VERSION <= 57
+      // BUG: Workaround Chrome WebGL 2 issue: the first shipped versions of WebGL 2 in Chrome did not actually implement the new WebGL 2 functions.
+      //      Those are supported only in Chrome 58 and newer. For Chrome 57 (and older), disable WebGL 2 support altogether.
+      function getChromeVersion() {
+        var raw = navigator.userAgent.match(/Chrom(e|ium)\/([0-9]+)\./);
+        return raw ? parseInt(raw[2], 10) : false;
+      }
+      if (getChromeVersion() <= 57) {
+        WebGL2RenderingContext = undefined;
+      }
+#endif
+
 #if GL_DEBUG
       var errorInfo = '?';
       function onContextCreationError(event) {
@@ -814,16 +826,6 @@ var LibraryGL = {
         GLctx: ctx
       };
 
-#if USE_WEBGL2
-      // BUG: Workaround Chrome WebGL 2 issue: the first shipped versions of WebGL 2 in Chrome did not actually implement the new WebGL 2 functions.
-      //      Those are supported only in Chrome 58 and newer.
-      function getChromeVersion() {
-        var raw = navigator.userAgent.match(/Chrom(e|ium)\/([0-9]+)\./);
-        return raw ? parseInt(raw[2], 10) : false;
-      }
-      context.supportsWebGL2EntryPoints = (context.version >= 2) && (getChromeVersion() === false || getChromeVersion() >= 58);
-#endif
-
 #if WORKAROUND_OLD_WEBGL_UNIFORM_UPLOAD_IGNORED_OFFSET_BUG
       context.cannotHandleOffsetsInUniformArrayViews = (function(g) {
         function b(c, t) {
@@ -1323,7 +1325,7 @@ var LibraryGL = {
   glCompressedTexImage2D__sig: 'viiiiiiii',
   glCompressedTexImage2D: function(target, level, internalFormat, width, height, border, imageSize, data) {
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       if (GLctx.currentPixelUnpackBufferBinding) {
         GLctx['compressedTexImage2D'](target, level, internalFormat, width, height, border, imageSize, data);
       } else {
@@ -1339,7 +1341,7 @@ var LibraryGL = {
   glCompressedTexSubImage2D__sig: 'viiiiiiiii',
   glCompressedTexSubImage2D: function(target, level, xoffset, yoffset, width, height, format, imageSize, data) {
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       if (GLctx.currentPixelUnpackBufferBinding) {
         GLctx['compressedTexSubImage2D'](target, level, xoffset, yoffset, width, height, format, imageSize, data);
       } else {
@@ -1497,7 +1499,7 @@ var LibraryGL = {
       }
     }
 #endif
-    if (GL.currentContext.supportsWebGL2EntryPoints) {
+    if (GL.currentContext.version >= 2) {
       // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       if (GLctx.currentPixelUnpackBufferBinding) {
         GLctx.texImage2D(target, level, internalFormat, width, height, border, format, type, pixels);
@@ -1528,7 +1530,7 @@ var LibraryGL = {
       if (type == 0x8d61/*GL_HALF_FLOAT_OES*/) type = 0x140B /*GL_HALF_FLOAT*/;
     }
 #endif
-    if (GL.currentContext.supportsWebGL2EntryPoints) {
+    if (GL.currentContext.version >= 2) {
       // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       if (GLctx.currentPixelUnpackBufferBinding) {
         GLctx.texSubImage2D(target, level, xoffset, yoffset, width, height, format, type, pixels);
@@ -1553,7 +1555,7 @@ var LibraryGL = {
   ],
   glReadPixels: function(x, y, width, height, format, type, pixels) {
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       if (GLctx.currentPixelPackBufferBinding) {
         GLctx.readPixels(x, y, width, height, format, type, pixels);
       } else {
@@ -1730,7 +1732,7 @@ var LibraryGL = {
     }
 #endif
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       if (data) {
         GLctx.bufferData(target, HEAPU8, usage, data, size);
       } else {
@@ -1749,7 +1751,7 @@ var LibraryGL = {
   glBufferSubData__sig: 'viiii',
   glBufferSubData: function(target, offset, size, data) {
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.bufferSubData(target, offset, HEAPU8, data, size);
       return;
     }
@@ -2166,7 +2168,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniform1iv(GL.uniforms[location], HEAP32, value>>2, count);
       return;
     }
@@ -2183,7 +2185,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniform2iv(GL.uniforms[location], HEAP32, value>>2, count*2);
       return;
     }
@@ -2200,7 +2202,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniform3iv(GL.uniforms[location], HEAP32, value>>2, count*3);
       return;
     }
@@ -2217,7 +2219,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniform4iv(GL.uniforms[location], HEAP32, value>>2, count*4);
       return;
     }
@@ -2234,7 +2236,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniform1fv(GL.uniforms[location], HEAPF32, value>>2, count);
       return;
     }
@@ -2266,7 +2268,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniform2fv(GL.uniforms[location], HEAPF32, value>>2, count*2);
       return;
     }
@@ -2299,7 +2301,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniform3fv(GL.uniforms[location], HEAPF32, value>>2, count*3);
       return;
     }
@@ -2333,7 +2335,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniform4fv(GL.uniforms[location], HEAPF32, value>>2, count*4);
       return;
     }
@@ -2368,7 +2370,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniformMatrix2fv(GL.uniforms[location], !!transpose, HEAPF32, value>>2, count*4);
       return;
     }
@@ -2403,7 +2405,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniformMatrix3fv(GL.uniforms[location], !!transpose, HEAPF32, value>>2, count*9);
       return;
     }
@@ -2443,7 +2445,7 @@ var LibraryGL = {
 #endif
 
 #if USE_WEBGL2
-    if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+    if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
       GLctx.uniformMatrix4fv(GL.uniforms[location], !!transpose, HEAPF32, value>>2, count*16);
       return;
     }
@@ -3486,7 +3488,7 @@ var LibraryGL = {
     GL.mappedBuffers[buffer] = null;
 
     if (!(mapping.access & 0x10)) /* GL_MAP_FLUSH_EXPLICIT_BIT */
-      if (GL.currentContext.supportsWebGL2EntryPoints) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
+      if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
         GLctx.bufferSubData(target, mapping.offset, HEAPU8, mapping.mem, mapping.length);
       } else {
         GLctx.bufferSubData(target, mapping.offset, HEAPU8.subarray(mapping.mem, mapping.mem+mapping.length));