Do not expose emulated ETC1 textures to WebGL

src/libANGLE/Caps.h

@@ -778,6 +778,9 @@ struct Limitations
 
     // PVRTC1 textures must be squares.
     bool squarePvrtc1 = false;
+
+    // ETC1 texture support is emulated.
+    bool emulatedEtc1 = false;
 };
 
 struct TypePrecision

src/libANGLE/Context.cpp

@@ -3722,6 +3722,12 @@ void Context::initCaps()
         }
     }
 
+    // Hide emulated ETC1 extension from WebGL contexts.
+    if (mWebGLContext && getLimitations().emulatedEtc1)
+    {
+        mSupportedExtensions.compressedETC1RGB8TextureOES = false;
+    }
+
     // If we're capturing application calls for replay, don't expose any binary formats to prevent
     // traces from trying to use cached results
     if (getFrameCapture()->enabled())

src/libANGLE/renderer/metal/DisplayMtl.mm

@@ -712,11 +712,16 @@ void DisplayMtl::initializeTextureCaps() const
     // Re-verify texture extensions.
     mNativeExtensions.setTextureExtensionSupport(mNativeTextureCaps);
 
-    // Enable ANGLE-specific ETC2/EAC extension that is not set by the call above.
+    // When ETC2/EAC formats are natively supported, enable ANGLE-specific extension string to
+    // expose them to WebGL. In other case, mark potentially-available ETC1 extension as emulated.
     if (supportsAppleGPUFamily(1) && gl::DetermineCompressedTextureETCSupport(mNativeTextureCaps))
     {
         mNativeExtensions.compressedTextureETC = true;
     }
+    else
+    {
+        mNativeLimitations.emulatedEtc1 = true;
+    }
 
     // Enable ASTC sliced 3D, requires MTLGPUFamilyApple3
     if (supportsAppleGPUFamily(3) && mNativeExtensions.textureCompressionASTCLDRKHR)

src/libANGLE/renderer/vulkan/vk_caps_utils.cpp

@@ -295,12 +295,17 @@ void RendererVk::ensureCapsInitialized() const
     // Enable GL_EXT_buffer_storage
     mNativeExtensions.bufferStorageEXT = true;
 
-    // To ensure that ETC2/EAC formats are enabled only on hardware that supports them natively,
-    // this flag is not set by the function above and must be set explicitly. It exposes
-    // ANGLE_compressed_texture_etc extension string.
-    mNativeExtensions.compressedTextureETC =
-        (mPhysicalDeviceFeatures.textureCompressionETC2 == VK_TRUE) &&
-        gl::DetermineCompressedTextureETCSupport(mNativeTextureCaps);
+    // When ETC2/EAC formats are natively supported, enable ANGLE-specific extension string to
+    // expose them to WebGL. In other case, mark potentially-available ETC1 extension as emulated.
+    if ((mPhysicalDeviceFeatures.textureCompressionETC2 == VK_TRUE) &&
+        gl::DetermineCompressedTextureETCSupport(mNativeTextureCaps))
+    {
+        mNativeExtensions.compressedTextureETC = true;
+    }
+    else
+    {
+        mNativeLimitations.emulatedEtc1 = true;
+    }
 
     // Vulkan doesn't support ASTC 3D block textures, which are required by
     // GL_OES_texture_compression_astc.