Allow glBindBuffer with an unknown buffer (#23525)

Apparently the correct behavior is just to create one.

Fixes: #18886

Author: sbc100

src/lib/libwebgl.js

@@ -348,6 +348,13 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
       for (var i = table.length; i < ret; i++) {
         table[i] = null;
       }
+#if FULL_ES2
+      // Skip over any non-null elements that might have been created by
+      // glBindBuffer.
+      while (table[ret]) {
+        ret = GL.counter++;
+      }
+#endif
       return ret;
     },
 
@@ -2971,6 +2978,16 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
   },
 
   glBindBuffer: (target, buffer) => {
+#if FULL_ES2
+    // Calling glBindBuffer with an unknown buffer will implicitly create a
+    // new one.  Here we bypass `GL.counter` and directly using the ID passed
+    // in.
+    if (buffer && !GL.buffers[buffer]) {
+      var b = GLctx.createBuffer();
+      b.name = buffer;
+      GL.buffers[buffer] = b;
+    }
+#endif
 #if GL_ASSERTIONS
     GL.validateGLObjectID(GL.buffers, buffer, 'glBindBuffer', 'buffer');
 #endif

test/browser/webgl_create_context.cpp

@@ -155,8 +155,14 @@ int main() {
     printf("\n");
 
     // Test bug https://github.com/emscripten-core/emscripten/issues/1330:
+
+#if FULL_ES2
+    // Test bug https://github.com/emscripten-core/emscripten/issues/18886
+    unsigned vb = 100;
+#else
     unsigned vb;
     glGenBuffers(1, &vb);
+#endif
     glBindBuffer(GL_ARRAY_BUFFER, vb);
     glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
 
@@ -180,6 +186,9 @@ int main() {
     glGetVertexAttribiv(0, GL_VERTEX_ATTRIB_ARRAY_ENABLED, &enabled);
     assert(enabled == 0);
 
+#if FULL_ES2
+    glDeleteBuffers(1, &vb);
+#endif
     // Test that deleting the context works.
     res = emscripten_webgl_destroy_context(context);
     assert(res == 0);

test/test_browser.py

@@ -2635,7 +2635,7 @@ def test_html5_webgl_create_context_no_antialias(self, args):
   @parameterized({
     '': ([],),
     'closure': (['-O2', '-g1', '--closure=1'],),
-    'full_es2': (['-sFULL_ES2'],),
+    'full_es2': (['-sFULL_ES2', '-DFULL_ES2', '-sGL_ASSERTIONS'],),
     'pthread': (['-pthread'],),
   })
   def test_html5_webgl_create_context(self, args):