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MetalANGLE: OpenGL ES to Metal API translation layer

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MetalANGLE - OpenGL ES to Apple Metal API Translation Layer

Build Status Build Status

This is a fork of Google's ANGLE project. It adds Metal API backend support. Apple announced OpenGL (ES) deprecation in 2018. So the purpose of MetalANGLE is to allow OpenGL ES applications to continue operate on Apple platforms by translating OpenGL ES draw calls to Metal draw calls under the hood. It also supports OpenGL ES & Metal's interop.

30 Jun 2021 Update: Most of this repo's OpenGL ES 3.0 implementing code in Metal has been merged into official

repo. Initially, this was the only place where Metal backend's developments took place. It is not true anymore as
are also making modifications and are in a progress of merging their changes into official
. See current Differences between MetalANGLE and official ANGLE.

Preliminary Metal based WebGL benchmarks (based on gles3-dev branch code):

Current Metal backend implementation status

  • MetalANGLE has been migrated into official ANGLE repo. See current Differences between MetalANGLE and official ANGLE.
  • OpenGL ES 2.0 functionalities are 100% completed.
  • OpenGL ES 3.0 status:
    • [x] Occlusion queries.
    • [x] MSAA.
    • [x] Multiple render targets (Not all GL formats are supported on old iOS GPUs due to pixel storage's limits. See #issue 64).
    • [x] 3D, array, shadow textures.
    • [x] Texture swizzles (supported on iOS 13.0+, macOS 10.15+ only).
    • [x] Uniform buffers.
    • [x] Fence sync (supported on iOS 12.0+, macOS 10.14+ only).
    • [x] Pixel buffer objects.
    • [ ] Primitive Restart. Metal's primitive restart doesn't work reliably.
    • [ ] Flat shading with last provoking vertex. Metal's default is first provoking vertex.
    • [x] Transform feedbacks.
  • OpenGL ES 1.0 is not recommended to be used. Its implementation is not actively maintained by original
    project and currently buggy/not fully compliant.
  • All basic samples are working.
  • Almost all of ANGLE end2end tests have been passed. See List of failed tests.
  • 98% of OpenGL ES 2.0 conformance tests passed. 90%+ of OpenGL ES 3.0 conformance tests passed. See Khronos VK-GL-CTS.
  • These extensions have been implemented:
  • MGLKit utilities classes have been added. Providing kind of similar functionalies to Apples's GLKit.
  • Urho3D engine's demos have been tested using MetalANGLE without issues. See Urho3D's MetalANGLE integration testing branch.
  • Irrlicht Engine's integration with MetalANGLE sample:
  • Interop with Metal is supported, see Qt example:
  • ~~No
    support in draw calls yet.~~
  • Metal doesn't allow buffer offset not being multiple of 4 bytes or multiple of attribute's size. Hence, draw calls that use unsupported offsets, strides, and vertex formats will force MetalANGLE to do conversions on the fly.
  • ~~MSAA is not supported yet.~~
  • Old OpenGL ES 2.0 only implementation can be found on gles2 branch
  • Platforms supports:
    • MetalANGLE only supports MacOS 10.13+ for Mac.
    • For iOS, the min supported version is iOS 9.0. However, Metal acceleration is only available for iOS 11.0+, any version prior to that will fall back to use native Apple OpenGL ES implementation instead of Metal. Furthermore, most of the sample apps are compiled for iOS 11.0+. So if you want to test the sample apps on 10.0 devices and below, it won't run, except a few ones (e.g. MGLKitSampleApp_ios9.0).
    • iPhone 5 and below are not supported.
    • MacCatalyst 13.0+ is supported. #### TODO lists
  • [ ] Make sure it passes all ANGLE's tests.
  • [x] ~~Support
    by generating index buffer on the fly using Metal compute shader.~~
  • [x] ~~Use compute shader to convert unsupported offsets, strides & vertex formats.~~
  • [x] ~~Support MSAA.~~
  • [ ] Fully support OpenGL ES 3.0.

How to build Metal ANGLE for MacOS & iOS

View the Metal backend's Dev setup instructions.

Currently, for convenience, MetalANGLE can also be built using an Xcode project provided in

folder. The Xcode project also builds MGLKit utilities wrapper library which provides
, similar to Apple's provided GLKit classes such as
. Please open
for example iOS app using this
library. This documents contains some guides to port
apps to use

Nevertheless, you still need to setup the required environment and dependencies properly as mentioned in Metal backend's Dev setup instructions first.

Differences between MetalANGLE and Google's ANGLE

  • Before June 2021, most of the Metal back-end code are shared between
  • From Aug-Sep 2021 onward, there would be some changes from
    directly to
    repo. Those changes might not be included in
    because of some development conflicts. Most of the Apple's changes benefit the Webkit's WebGL standards and might not have optimal performance for normal uses. These changes from Apple include:
    • Rewriting the index buffer on the fly to support last provoking vertex of flat shading. While this helps conforming to OpenGL ES's flat shading's specifications, it makes draw calls using flat shading become slower. In majority of use cases, user wouldn't care whether flat shading uses last or first provoking vertex.
  • MetalANGLE
    includes iOS supports and high level API such as MGLKit that mimics Apple's deprecated
    API. These features are unlikely to be merged into
    project doesn't have any plan to support iOS in near future.

Google's ANGLE - Almost Native Graphics Layer Engine

The goal of ANGLE is to allow users of multiple operating systems to seamlessly run WebGL and other OpenGL ES content by translating OpenGL ES API calls to one of the hardware-supported APIs available for that platform. ANGLE currently provides translation from OpenGL ES 2.0 and 3.0 to desktop OpenGL, OpenGL ES, Direct3D 9, and Direct3D 11. Support for translation from OpenGL ES to Vulkan is underway, and future plans include compute shader support (ES 3.1) and MacOS support.

Level of OpenGL ES support via backing renderers

| | Direct3D 9 | Direct3D 11 | Desktop GL | GL ES | Vulkan | Metal | |----------------|:-------------:|:----------------:|:--------------:|:-------------:|:-------------:|:-------------:| | OpenGL ES 2.0 | complete | complete | complete | complete | complete | complete | | OpenGL ES 3.0 | | complete | complete | complete | in progress | 90% complete | | OpenGL ES 3.1 | | in progress | complete | complete | in progress | | | OpenGL ES 3.2 | | | planned | planned | planned | |

Platform support via backing renderers

| | Direct3D 9 | Direct3D 11 | Desktop GL | GL ES | Vulkan | Metal | |------------:|:--------------:|:--------------:|:-------------:|:-----------:|:-----------:|:-----------:| | Windows | complete | complete | complete | complete | complete | | | Linux | | | complete | | complete | | | Mac OS X | | | complete | | | complete | | iOS | | | | | | complete | | Chrome OS | | | | complete | planned | | | Android | | | | complete | complete | | | Fuchsia | | | | | in progress | |

ANGLE v1.0.772 was certified compliant by passing the ES 2.0.3 conformance tests in October 2011. ANGLE also provides an implementation of the EGL 1.4 specification.

ANGLE is used as the default WebGL backend for both Google Chrome and Mozilla Firefox on Windows platforms. Chrome uses ANGLE for all graphics rendering on Windows, including the accelerated Canvas2D implementation and the Native Client sandbox environment.

Portions of the ANGLE shader compiler are used as a shader validator and translator by WebGL implementations across multiple platforms. It is used on Mac OS X, Linux, and in mobile variants of the browsers. Having one shader validator helps to ensure that a consistent set of GLSL ES shaders are accepted across browsers and platforms. The shader translator can be used to translate shaders to other shading languages, and to optionally apply shader modifications to work around bugs or quirks in the native graphics drivers. The translator targets Desktop GLSL, Direct3D HLSL, and even ESSL for native GLES2 platforms.


ANGLE repository is hosted by Chromium project and can be browsed online or cloned with

git clone


View the Dev setup instructions.


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