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GL 4.0 folds ARB_transform_feedback2 and _3 into core, and neither existed: glGenTransformFeedbacks, glBindTransformFeedback, glDeleteTransformFeedbacks, glIsTransformFeedback, glPause/ResumeTransformFeedback, the whole glDrawTransformFeedback family and glBegin/EndQueryIndexed were all stubs, and gl_NextBuffer / gl_SkipComponents1..4 failed the link as "not an output of the vertex stage". Seven KHR-GL40.transform_feedback* cases failed on it, three of them by leaving a capture open at deinit and taking the process down. Objects. The capture state and the indexed GL_TRANSFORM_FEEDBACK_BUFFER bindings are object state, but the context keeps one live copy of both, which is what every existing reader - each backend's per-draw sync, the drawing and getter paths - is written against. Rather than teach all of them about objects, a bind saves the live copy into the outgoing object and restores the incoming one's. Object 0 is the default object and needs no seeding; operator[] materialises the rest on first touch. Pause. A paused span captures nothing, and three rules key off that: a draw is exempt from the capture primitive-mode match, it feeds PRIMITIVES_GENERATED but not TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN, and glUseProgram is allowed again (that last one was already refused for an active capture, correctly for GL 3.3, which has no pause). glDrawTransformFeedback replays the vertices the object captured in its last completed span, recorded at End. "Has a completed span" is tracked separately from that count, because a completed empty span draws nothing while an object that never ended one is INVALID_OPERATION. Drawing from the object whose capture is currently open is deliberately allowed - feeding a result straight into the next span is the point of KHR-GL40.transform_feedback.draw_xfb_feedbackk_test. DirectGLES gets a real driver object per frontend object. That is the only reason the default one would not do: several objects can be paused at once, and a paused span lives inside the driver's object. The deferred driver-side Begin (still needed - ES wants the program current and the buffers bound) now also has to be held back while the span is paused, or a pause taken before the first draw would open the span on that draw and subject it to the primitive-mode rule it is exempt from. Special names. gl_NextBuffer and gl_SkipComponents<n> are consumed during varying resolution and never become varyings of their own, so they only move where the following ones land - and stay out of the name list the backend declares on its own driver. ES cannot express the resulting layout at all: it packs every captured varying into one gap-free record. So when the layout has holes or spans several buffers, DirectGLES captures into a scratch buffer bound in place of the application's, and End distributes the records to the offsets GL asked for. Only the bytes a varying occupies are written, which is exactly what makes the holes keep the contents the application left there - the property KHR-GL40.transform_feedback3.skip_components checks. glBegin/EndQueryIndexed and glGetQueryIndexediv differ from the plain forms only in the vertex stream they address, so they validate the index and forward. GL_MAX_VERTEX_STREAMS stays at 1: multi-stream capture needs ARB_gpu_shader5 stream qualifiers that no ES driver implements, and the CTS cases that need more than one stream check the limit and skip. KHR-GL40.transform_feedback, transform_feedback2 and transform_feedback3: 38/38.
MobileGL
A desktop OpenGL implementation
MobileGL is a free and open-source project that implements a desktop OpenGL API. The goal is to provide a complete desktop OpenGL implementation with a state management layer and multi-backend support.
Note
Status: In development. Parts of the codebase are incomplete. Current short-term target: OpenGL 3.3 (Core Profile).
Project positioning
MobileGL is an implementation of a desktop OpenGL library. It aims to provide:
- Full OpenGL state management.
- A front-end that exposes OpenGL functions.
- Multiple independent backend implementations, where each backend targets a specific graphics API and remains fully isolated from others.
This project is intended as an implementation/translation layer.
Key components
The repository is organized into following top-level modules:
- MG_State — state tracking and management logic for Graphics APIs.
- MG_Impl — front-end implementations of Graphics APIs that interact with
MG_StateandMG_Backend. - MG_Backend — per-backend translation layer that maps front-end Graphics APIs' semantics and state into concrete backend API calls (e.g. OpenGL ES, Vulkan).
- MG_Util and other utility modules.
Third-party components
MobileGL reuses several open-source projects:
- SPIRV-Cross by KhronosGroup - Apache License 2.0: github
- glslang by KhronosGroup - Various Licenses: github
- DiligentCore by Diligent Graphics - Apache License 2.0: github
Refer to each component's repository for exact license texts. Any bundled third-party code in this repository is included under the upstream project's license.
Compatibility & target
- Short-term target:
OpenGL 3.3 (Core Profile). - Current development focus:
MG_StateandMG_ImplforOpenGL 3.3 (Core Profile)Direct (Vulkan)backendDirect (OpenGL ES)backend
Build Instructions
We currently provide no releases and no precompiled binaries.
If you want to try the project right now, you’ll need to build it yourself:
-
Clone the repository:
git clone https://github.com/MobileGL-Dev/MobileGL.git -
Initialize and update all submodules recursively:
git submodule update --init --recursive -
Follow glslang’s own documentation for its required initiation.
-
Configure and build the project with CMake:
cmake -B build cmake --build buildor do it in a modern way:
cmake -S . -B build -G Ninja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ cmake --build buildAlternatively, you can use platform-specific build commands as needed.
Build For macOS
On macOS, MobileGL can be built as a dylib that exposes the normal OpenGL/CGL/NSOpenGL entry points and routes them to the DirectVulkan backend. This is useful for running applications such as Minecraft through their stock GLFW/LWJGL OpenGL path while MobileGL is injected before context creation.
Prerequisites:
- macOS with Clang and Ninja.
- Vulkan loader and MoltenVK installed. With Homebrew, the MoltenVK ICD is commonly located at
/opt/homebrew/etc/vulkan/icd.d/MoltenVK_icd.json.
Configure and build:
cmake -S . -B build-macos-magma \
-G Ninja \
-DCMAKE_BUILD_TYPE=Release \
-DMOBILEGL_BACKEND_TYPE=DirectVulkan \
-DMOBILEGL_BUILD_TEST=OFF \
-DMOBILEGL_BUILD_BENCHMARK=OFF
cmake --build build-macos-magma --target MobileGL -j8
The dylib will be generated at:
build-macos-magma/libMobileGL.dylib
To run Minecraft by MobileGL from a launcher like PrismLauncher, keep the stock LWJGL/GLFW natives and add a wrapper command to the instance settings:
env DYLD_INSERT_LIBRARIES=/absolute/path/to/MobileGL/build-macos-magma/libMobileGL.dylib MOBILEGL_BACKEND_TYPE=DirectVulkan VK_ICD_FILENAMES=/opt/homebrew/etc/vulkan/icd.d/MoltenVK_icd.json
Also make sure the JVM arguments include:
-XstartOnFirstThread
DYLD_INSERT_LIBRARIES must be active before GLFW creates its OpenGL context. After startup, the Minecraft F3 screen should report MobileGL and the Direct (Vulkan) backend if the injection worked.
Build Options
| Option | Description | Default |
|---|---|---|
MOBILEGL_BUILD_TEST |
Build MobileGL tests (requires Clang) | ON |
MOBILEGL_BUILD_BENCHMARK |
Build MobileGL benchmarks (requires Clang) | ON |
MOBILEGL_FORCE_RELEASE_OPT |
Enable O3 and LTO in Debug build | ON |
MOBILEGL_ENABLE_TRACY |
Enable Tracy profiler for performance analysis | OFF |
Notes:
- The project requires C++23.
MG_TestandMG_Benchmarkcan only be built with Clang, not GCC. To enforce Clang, add-DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++to your command.- On Android, tests and benchmarks are always disabled.
Environment Variables
MobileGL supports runtime configuration via environment variables.
Supported Keys
| Variable | Description | Allowed Values | Default |
|---|---|---|---|
MOBILEGL_BACKEND_TYPE |
Select active backend implementation at startup. | DirectGLES, DirectVulkan |
DirectGLES |
MOBILEGL_DISABLE_TIMERQUERY |
Disable GPU timer-query exposure and use. | 0, 1 |
0 |
MOBILEGL_USE_ANGLE |
Load ANGLE EGL/GLES libraries. | 0, 1 |
0 |
MOBILEGL_DISABLE_SUBGROUP |
Disable Vulkan shader subgroup support. | 0, 1 |
0 |
MOBILEGL_MAGMA_R11G11B10F_FALLBACK |
Use Magma's R11G11B10F format fallback. | 0, 1 |
0 |
MOBILEGL_MAGMA_FRAMESINFLIGHT |
Set Magma frames in flight. | Integer 1–64 |
3 |
MOBILEGL_AVOID_SAMPLER_MIPMAP_MIN_FILTER |
Avoid sampler mipmap minification filters. | 0, 1 |
0 |
MOBILEGL_COHERENT_AS_FLUSH |
Treat persistent GL_MAP_FLUSH_EXPLICIT_BIT maps as coherent (app-compat for engines like Flywheel that never flush them). |
0, 1 |
0 |
VK_ICD_FILENAMES |
Select the Vulkan ICD used by the Vulkan loader. | Path to an ICD JSON file | Loader default |
Notice
- MobileGL is not production-ready currently.
- Some
OpenGL 3.3 (Core Profile)features are still missing or under development.
License
This project is distributed under GNU LGPL v3.0. See the LICENSE file in the repository for detailed information.