LibWeb/WebGL: Make getExtension spec-compliant

Namely:
- Perform case-insensitive matching
- Return the same extension objects every time
- Only enable the extension if it's supported by the current context

Libraries/LibWeb/Forward.h

@@ -841,6 +841,8 @@ struct OscillatorOptions;
 }
 
 namespace Web::WebGL {
+class ANGLEInstancedArrays;
+class OESVertexArrayObject;
 class OpenGLContext;
 class WebGL2RenderingContext;
 class WebGLActiveInfo;
@@ -858,6 +860,7 @@ class WebGLSync;
 class WebGLTexture;
 class WebGLUniformLocation;
 class WebGLVertexArrayObject;
+class WebGLVertexArrayObjectOES;
 }
 
 namespace Web::WebIDL {

Libraries/LibWeb/WebGL/WebGLRenderingContext.cpp

@@ -11,6 +11,7 @@
 #include <LibWeb/Bindings/WebGLRenderingContextPrototype.h>
 #include <LibWeb/HTML/HTMLCanvasElement.h>
 #include <LibWeb/HTML/TraversableNavigable.h>
+#include <LibWeb/Infra/Strings.h>
 #include <LibWeb/Painting/Paintable.h>
 #include <LibWeb/WebGL/ANGLEInstancedArrays.h>
 #include <LibWeb/WebGL/EventNames.h>
@@ -89,6 +90,8 @@ void WebGLRenderingContext::visit_edges(Cell::Visitor& visitor)
     Base::visit_edges(visitor);
     WebGLRenderingContextImpl::visit_edges(visitor);
     visitor.visit(m_canvas_element);
+    visitor.visit(m_angle_instanced_arrays_extension);
+    visitor.visit(m_oes_vertex_array_object_extension);
 }
 
 void WebGLRenderingContext::present()
@@ -174,12 +177,36 @@ Optional<Vector<String>> WebGLRenderingContext::get_supported_extensions()
 
 JS::Object* WebGLRenderingContext::get_extension(String const& name)
 {
-    if (name == "ANGLE_instanced_arrays"sv) {
-        return MUST(ANGLEInstancedArrays::create(realm()));
+    // Returns an object if, and only if, name is an ASCII case-insensitive match [HTML] for one of the names returned
+    // from getSupportedExtensions; otherwise, returns null. The object returned from getExtension contains any constants
+    // or functions provided by the extension. A returned object may have no constants or functions if the extension does
+    // not define any, but a unique object must still be returned. That object is used to indicate that the extension has
+    // been enabled.
+    auto supported_extensions = get_supported_extensions();
+    auto supported_extension_iterator = supported_extensions->find_if([&name](String const& supported_extension) {
+        return Infra::is_ascii_case_insensitive_match(supported_extension, name);
+    });
+    if (supported_extension_iterator == supported_extensions->end())
+        return nullptr;
+
+    if (Infra::is_ascii_case_insensitive_match(name, "ANGLE_instanced_arrays"sv)) {
+        if (!m_angle_instanced_arrays_extension) {
+            m_angle_instanced_arrays_extension = MUST(ANGLEInstancedArrays::create(realm(), *this));
+        }
+
+        VERIFY(m_angle_instanced_arrays_extension);
+        return m_angle_instanced_arrays_extension;
     }
-    if (name == "OES_vertex_array_object"sv) {
-        return MUST(OESVertexArrayObject::create(realm(), *this));
+
+    if (Infra::is_ascii_case_insensitive_match(name, "OES_vertex_array_object"sv)) {
+        if (!m_oes_vertex_array_object_extension) {
+            m_oes_vertex_array_object_extension = MUST(OESVertexArrayObject::create(realm(), *this));
+        }
+
+        VERIFY(m_oes_vertex_array_object_extension);
+        return m_oes_vertex_array_object_extension;
     }
+
     return nullptr;
 }
 

Libraries/LibWeb/WebGL/WebGLRenderingContext.h

@@ -79,6 +79,11 @@ private:
 
     GLenum m_error { 0 };
 
+    // Extensions
+    // "Multiple calls to getExtension with the same extension string, taking into account case-insensitive comparison, must return the same object as long as the extension is enabled."
+    GC::Ptr<ANGLEInstancedArrays> m_angle_instanced_arrays_extension;
+    GC::Ptr<OESVertexArrayObject> m_oes_vertex_array_object_extension;
+
     virtual void set_error(GLenum error) override;
 };