Apply max draw buffer limit for WebGL shaders.

src/libANGLE/Caps.cpp

@@ -594,7 +594,7 @@ const ExtensionInfoMap &GetExtensionInfoMap()
         map["GL_OES_depth32"] = esOnlyExtension(&Extensions::depth32);
         map["GL_EXT_texture_storage"] = esOnlyExtension(&Extensions::textureStorage);
         map["GL_OES_texture_npot"] = enableableExtension(&Extensions::textureNPOT);
-        map["GL_EXT_draw_buffers"] = esOnlyExtension(&Extensions::drawBuffers);
+        map["GL_EXT_draw_buffers"] = enableableExtension(&Extensions::drawBuffers);
         map["GL_EXT_texture_filter_anisotropic"] = esOnlyExtension(&Extensions::textureFilterAnisotropic);
         map["GL_EXT_occlusion_query_boolean"] = esOnlyExtension(&Extensions::occlusionQueryBoolean);
         map["GL_NV_fence"] = esOnlyExtension(&Extensions::fence);

src/libANGLE/Compiler.cpp

@@ -110,6 +110,11 @@ Compiler::Compiler(rx::GLImplFactory *implFactory, const ContextState &state)
     mResources.MaxFragmentAtomicCounterBuffers = caps.maxFragmentAtomicCounterBuffers;
     mResources.MaxCombinedAtomicCounterBuffers = caps.maxCombinedAtomicCounterBuffers;
     mResources.MaxAtomicCounterBufferSize      = caps.maxAtomicCounterBufferSize;
+
+    if (state.getClientMajorVersion() == 2 && !extensions.drawBuffers)
+    {
+        mResources.MaxDrawBuffers = 1;
+    }
 }
 
 Compiler::~Compiler()

src/libANGLE/Context.cpp

@@ -2293,11 +2293,14 @@ void Context::initExtensionStrings()
     }
     mExtensionString = mergeExtensionStrings(mExtensionStrings);
 
+    const gl::Extensions &nativeExtensions = mImplementation->getNativeExtensions();
+
     mRequestableExtensionStrings.clear();
     for (const auto &extensionInfo : GetExtensionInfoMap())
     {
         if (extensionInfo.second.Requestable &&
-            !(mExtensions.*(extensionInfo.second.ExtensionsMember)))
+            !(mExtensions.*(extensionInfo.second.ExtensionsMember)) &&
+            nativeExtensions.*(extensionInfo.second.ExtensionsMember))
         {
             mRequestableExtensionStrings.push_back(MakeStaticString(extensionInfo.first));
         }
@@ -2370,6 +2373,10 @@ void Context::requestExtension(const char *name)
     mExtensions.*(extension.ExtensionsMember) = true;
     updateCaps();
     initExtensionStrings();
+
+    // Re-create the compiler with the requested extensions enabled.
+    SafeDelete(mCompiler);
+    mCompiler = new Compiler(mImplementation.get(), mState);
 }
 
 size_t Context::getRequestableExtensionStringCount() const

src/libANGLE/ContextState.cpp

@@ -151,8 +151,6 @@ bool ValidationContext::getQueryParameterInfo(GLenum pname, GLenum *type, unsign
         case GL_MAX_TEXTURE_IMAGE_UNITS:
         case GL_MAX_FRAGMENT_UNIFORM_VECTORS:
         case GL_MAX_RENDERBUFFER_SIZE:
-        case GL_MAX_COLOR_ATTACHMENTS_EXT:
-        case GL_MAX_DRAW_BUFFERS_EXT:
         case GL_NUM_SHADER_BINARY_FORMATS:
         case GL_NUM_COMPRESSED_TEXTURE_FORMATS:
         case GL_ARRAY_BUFFER_BINDING:
@@ -214,6 +212,17 @@ bool ValidationContext::getQueryParameterInfo(GLenum pname, GLenum *type, unsign
             *numParams = 1;
             return true;
         }
+        case GL_MAX_DRAW_BUFFERS_EXT:
+        case GL_MAX_COLOR_ATTACHMENTS_EXT:
+        {
+            if ((getClientMajorVersion() < 3) && !getExtensions().drawBuffers)
+            {
+                return false;
+            }
+            *type      = GL_INT;
+            *numParams = 1;
+            return true;
+        }
         case GL_MAX_SAMPLES_ANGLE:
         {
             if (!getExtensions().framebufferMultisample)

src/tests/gl_tests/WebGLCompatibilityTest.cpp

@@ -589,6 +589,44 @@ TEST_P(WebGLCompatibilityTest, TextureCopyingFeedbackLoops)
     EXPECT_GL_NO_ERROR();
 }
 
+// Test for the max draw buffers and color attachments.
+TEST_P(WebGLCompatibilityTest, MaxDrawBuffersAttachmentPoints)
+{
+    // This test only applies to ES2.
+    if (getClientMajorVersion() != 2)
+    {
+        return;
+    }
+
+    GLFramebuffer fbo[2];
+    glBindFramebuffer(GL_FRAMEBUFFER, fbo[0].get());
+
+    // Test that is valid when we bind with a single attachment point.
+    GLTexture texture;
+    glBindTexture(GL_TEXTURE_2D, texture.get());
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture.get(), 0);
+    ASSERT_GL_NO_ERROR();
+
+    // Test that enabling the draw buffers extension will allow us to bind with a non-zero
+    // attachment point.
+    if (extensionRequestable("GL_EXT_draw_buffers"))
+    {
+        glRequestExtensionANGLE("GL_EXT_draw_buffers");
+        EXPECT_GL_NO_ERROR();
+        EXPECT_TRUE(extensionEnabled("GL_EXT_draw_buffers"));
+
+        glBindFramebuffer(GL_FRAMEBUFFER, fbo[1].get());
+
+        GLTexture texture2;
+        glBindTexture(GL_TEXTURE_2D, texture2.get());
+        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
+        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, texture2.get(),
+                               0);
+        ASSERT_GL_NO_ERROR();
+    }
+}
+
 // Use this to select which configurations (e.g. which renderer, which GLES major version) these
 // tests should be run against.
 ANGLE_INSTANTIATE_TEST(WebGLCompatibilityTest,