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- VulkanRenderer::CurrentXfbCounterSlot keyed m_xfbCounterSlotByObject on
GetBoundTransformFeedbackName(). glGenTransformFeedbacks hands a deleted name
straight back (IndexGenerator is LIFO) and nothing ever removed a map entry, so
a transform feedback object created on a recycled name was served the DEAD
object's counter group - and with it that group's m_xfbCountersValid and
m_xfbLastSeenGeneration entries, which are the resume/fresh decision for
vkCmdBeginTransformFeedbackEXT. This is D21 in plan B v2 4.7.3, the one entry
in that table whose today-key "guards nothing", and 10.4-5 asks for it to land
on dev on its own - hence this separate commit, kept in files no other commit
on this branch touches so the cherry-pick applies unaided.
- Frontend: TransformFeedbackObjectState gains a never-reused `lifetimeId`
through a default member initialiser, so every route into existence
(operator[] materialisation, `= {}` in GenTransformFeedbackNames and
CreateTransformFeedbackObject) mints a fresh one and a recycled name cannot
carry the dead object's id back. The allocator is the same shape as
BufferObject::AllocateLifetimeId (atomic, starts at 1 so a zeroed backend slot
is never a live object).
- The bound object's id is mirrored in m_boundTransformFeedbackLifetimeId,
refreshed by RestoreBoundTransformFeedbackState - which every bind, and the
revert that deleting the bound object performs, goes through - and seeded for
the default object by the GLContext constructor. GetBoundTransformFeedback
LifetimeId is therefore a const load. Reading it through operator[] instead
would have been an INSERT on the per-draw path, and UnorderedMap is
ska::flat_hash_map, whose rehash invalidates every reference into the
container, not just its iterators.
- Backend: the UnorderedMap is replaced by a fixed 16-entry owner table, which
fixes the second half of the same defect - the map was keyed on a value that
recycles yet was never pruned, so it grew for the life of the context. With
lifetime ids as keys a map would have grown without bound instead, so the
bounded table is required, not cosmetic.
- Slot exhaustion: past sixteen owners a group has to be taken over, and the
victim is chosen among owners with NO OPEN SPAN, which
GLContext::HasOpenTransformFeedbackSpan answers; an identity no live object
carries any more answers false, and that is what lets a dead owner's group
come back. Least-recently-used ALONE would have been exactly the wrong rule:
GL only permits another object to capture while this one is PAUSED, so the
paused span these groups exist to protect is by construction the least
recently used entry, and an LRU takeover would reset the one resume offset
that still matters. LRU is now only the tie-break among reclaimable groups.
Sixteen genuinely open spans at once is reported (MGLOG_E_ONCE) rather than
resolved silently, because whatever is taken then restarts at offset 0.
- Not done, and why: the natural place to hand a group back is
glEndTransformFeedback, but registering DirectVulkan's EndTransformFeedback
table entry would flip the test FixupGsStripCaptureOrder makes of that same
pointer (GL_Drawing.cpp:1255) to decide whether the backend already captured
in GL's vertex order, silently disabling the geometry-stage strip fixup for
DirectVulkan. Giving that discriminator a name of its own is a separate
change; until then the no-open-span rule is what keeps the table honest.
- CurrentXfbCounterSlot asserts the identity is never 0. Zero is the free-slot
sentinel, so an identity of 0 would match every free slot as "mine" without
ever claiming one - this bug reintroduced, with no symptom at the call site.
- TransformFeedbackLifetimeIdTest, in its own translation unit, pins the
frontend halves: an object created on a recycled name must not report the dead
object's id, the default object has an identity before anything binds it, and
a PAUSED span still reads as open while another object is bound and capturing
- which is the whole correctness argument for the eviction rule. The name
reuse is not simulated: the test asks the real generator and skips (loudly) if
it never recycled. Still untested: the >16-owners path itself, which needs a
backend scenario with seventeen capturing objects and there is none.
- Negative controls, each applied then reverted: making a non-bound object's
span read as closed reddens APausedSpanStaysOpenWhileAnotherObjectCaptures;
making a vanished identity read as open reddens the same case on its delete
assertion; dropping the constructor's seeding reddens
AnObjectAtARecycledNameCarriesAFreshLifetimeId.
- Tested: cmake --build build-linux -j 24 (clean, 166 targets); ctest -L unit
-j 12 -> 1386/1386 passed; ctest -L integration-gpu -> 866/866 passed
serially, and 866/866 on one of two -j 8 runs. The other -j 8 run failed
DirectGLES.PointSizeDemotionScenario.TheDemotionIsActuallyArmedWhenTheEnviron
mentPinsItOn, a member of the pre-existing parallel-ctest flake family: it
passes in isolation here, and the unmodified parent tree
(~/w7/p0-noop-wins-base) reproduces the same family under -j 8.
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 4.2 (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
- flat_hash_map by Malte Skarupke - Boost Software License 1.0: 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 4.2 (Core Profile). - Current development focus:
- Performance improvement
MG_StateandMG_ImplforOpenGL 4.2 (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_ESPRYT_USE_ANGLE |
Load ANGLE EGL/GLES libraries. | 0, 1 |
0 |
MOBILEGL_MAGMA_DISABLE_SUBGROUP |
Disable Vulkan shader subgroup support. | 0, 1 |
0 |
MOBILEGL_ADVERTISE_FP64 |
Advertise GL_ARB_gpu_shader_fp64. GLSL double/dvec/dmat compile and run either way - they are narrowed to 32 bits - so this only changes whether an application is told it has 64-bit precision, which it does not. |
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_ESPRYT_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 |
MOBILEGL_ESPRYT_FORCE_DS_READBACK_EMULATION |
Always emulate depth/stencil glReadPixels/glGetTexImage by shader sampling on Espryt, instead of using the driver's own depth/stencil readback where it has one. |
0, 1 |
0 |
VK_ICD_FILENAMES |
Select the Vulkan ICD used by the Vulkan loader. | Path to an ICD JSON file | Loader default |
License
This project is distributed under GNU LGPL v3.0. See the LICENSE file in the repository for detailed information.